Updated java.library.path.

briar-api/src/main/java/org/briarproject/briar/api/blog/Blog.java

@@ -0,0 +1,39 @@
+package org.briarproject.briar.api.blog;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.briar.api.client.BaseGroup;
+import org.briarproject.briar.api.sharing.Shareable;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class Blog extends BaseGroup implements Shareable {
+
+	private final Author author;
+
+	public Blog(Group group, Author author) {
+		super(group);
+		this.author = author;
+	}
+
+	public Author getAuthor() {
+		return author;
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof Blog && super.equals(o);
+	}
+
+	/**
+	 * Returns the blog's author's name, not the name as shown in the UI.
+	 */
+	@Override
+	public String getName() {
+		return author.getName();
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/BlogCommentHeader.java

@@ -0,0 +1,46 @@
+package org.briarproject.briar.api.blog;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.identity.Author.Status;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+import static org.briarproject.briar.api.blog.MessageType.COMMENT;
+import static org.briarproject.briar.api.blog.MessageType.WRAPPED_COMMENT;
+
+@Immutable
+@NotNullByDefault
+public class BlogCommentHeader extends BlogPostHeader {
+
+	@Nullable
+	private final String comment;
+	private final BlogPostHeader parent;
+
+	public BlogCommentHeader(MessageType type, GroupId groupId,
+			@Nullable String comment, BlogPostHeader parent, MessageId id,
+			long timestamp, long timeReceived, Author author,
+			Status authorStatus, boolean read) {
+
+		super(type, groupId, id, parent.getId(), timestamp,
+				timeReceived, author, authorStatus, read);
+
+		if (type != COMMENT && type != WRAPPED_COMMENT)
+			throw new IllegalArgumentException("Incompatible Message Type");
+
+		this.comment = comment;
+		this.parent = parent;
+	}
+
+	@Nullable
+	public String getComment() {
+		return comment;
+	}
+
+	public BlogPostHeader getParent() {
+		return parent;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/BlogConstants.java

@@ -0,0 +1,50 @@
+package org.briarproject.briar.api.blog;
+
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
+
+public interface BlogConstants {
+
+	/**
+	 * The maximum length of a blogs's name in UTF-8 bytes.
+	 */
+	int MAX_BLOG_TITLE_LENGTH = 100;
+
+	/**
+	 * The length of a blogs's description in UTF-8 bytes.
+	 */
+	int MAX_BLOG_DESC_LENGTH = 240;
+
+	/**
+	 * The maximum length of a blog post's body in bytes.
+	 */
+	int MAX_BLOG_POST_BODY_LENGTH = MAX_MESSAGE_BODY_LENGTH - 1024;
+
+	/**
+	 * The maximum length of a blog comment in bytes.
+	 */
+	int MAX_BLOG_COMMENT_LENGTH = MAX_BLOG_POST_BODY_LENGTH;
+
+	/* Blog Sharing Constants */
+	String BLOG_AUTHOR_NAME = "blogAuthorName";
+	String BLOG_PUBLIC_KEY = "blogPublicKey";
+
+	// Metadata keys
+	String KEY_TYPE = "type";
+	String KEY_DESCRIPTION = "description";
+	String KEY_TIMESTAMP = "timestamp";
+	String KEY_TIME_RECEIVED = "timeReceived";
+	String KEY_AUTHOR_ID = "id";
+	String KEY_AUTHOR_NAME = "name";
+	String KEY_PUBLIC_KEY = "publicKey";
+	String KEY_AUTHOR = "author";
+	String KEY_READ = "read";
+	String KEY_COMMENT = "comment";
+	String KEY_ORIGINAL_MSG_ID = "originalMessageId";
+	String KEY_ORIGINAL_PARENT_MSG_ID = "originalParentMessageId";
+	/**
+	 * This is the ID of either a message wrapped from a different group
+	 * or of a message from the same group that therefore needed no wrapping.
+	 */
+	String KEY_PARENT_MSG_ID = "parentMessageId";
+
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/BlogFactory.java

@@ -0,0 +1,21 @@
+package org.briarproject.briar.api.blog;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Group;
+
+@NotNullByDefault
+public interface BlogFactory {
+
+	/**
+	 * Creates a personal blog for a given author.
+	 */
+	Blog createBlog(Author author);
+
+	/**
+	 * Parses a blog with the given Group
+	 */
+	Blog parseBlog(Group g) throws FormatException;
+
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/BlogInvitationRequest.java

@@ -0,0 +1,31 @@
+package org.briarproject.briar.api.blog;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.SessionId;
+import org.briarproject.briar.api.sharing.InvitationRequest;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+public class BlogInvitationRequest extends InvitationRequest {
+
+	private final String blogAuthorName;
+
+	public BlogInvitationRequest(MessageId id, SessionId sessionId,
+			GroupId groupId, ContactId contactId, String blogAuthorName,
+			@Nullable String message, boolean available, long time,
+			boolean local, boolean sent, boolean seen, boolean read) {
+
+		super(id, sessionId, groupId, contactId, message, available, time,
+				local, sent, seen, read);
+		this.blogAuthorName = blogAuthorName;
+	}
+
+	public String getBlogAuthorName() {
+		return blogAuthorName;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/BlogInvitationResponse.java

@@ -0,0 +1,21 @@
+package org.briarproject.briar.api.blog;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.SessionId;
+import org.briarproject.briar.api.sharing.InvitationResponse;
+
+@NotNullByDefault
+public class BlogInvitationResponse extends InvitationResponse {
+
+	public BlogInvitationResponse(MessageId id, SessionId sessionId,
+			GroupId groupId, ContactId contactId, boolean accept, long time,
+			boolean local, boolean sent, boolean seen, boolean read) {
+
+		super(id, sessionId, groupId, contactId, accept, time, local, sent,
+				seen, read);
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/BlogManager.java

@@ -0,0 +1,105 @@
+package org.briarproject.briar.api.blog;
+
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.identity.LocalAuthor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.ClientId;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import java.util.Collection;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+public interface BlogManager {
+
+	/**
+	 * Unique ID of the blog client.
+	 */
+	ClientId CLIENT_ID = new ClientId("org.briarproject.briar.blog");
+
+	/**
+	 * Returns true if a blog can be removed.
+	 */
+	boolean canBeRemoved(GroupId g) throws DbException;
+
+	/**
+	 * Removes and deletes a blog.
+	 */
+	void removeBlog(Blog b) throws DbException;
+
+	/**
+	 * Stores a local blog post.
+	 */
+	void addLocalPost(BlogPost p) throws DbException;
+
+	/**
+	 * Stores a local blog post.
+	 */
+	void addLocalPost(Transaction txn, BlogPost p) throws DbException;
+
+	/**
+	 * Adds a comment to an existing blog post or reblogs it.
+	 */
+	void addLocalComment(LocalAuthor author, GroupId groupId,
+			@Nullable String comment, BlogPostHeader wHeader)
+			throws DbException;
+
+	/**
+	 * Returns the blog with the given ID.
+	 */
+	Blog getBlog(GroupId g) throws DbException;
+
+	/**
+	 * Returns the blog with the given ID.
+	 */
+	Blog getBlog(Transaction txn, GroupId g) throws DbException;
+
+	/**
+	 * Returns all blogs owned by the given localAuthor.
+	 */
+	Collection<Blog> getBlogs(LocalAuthor localAuthor) throws DbException;
+
+	/**
+	 * Returns only the personal blog of the given author.
+	 */
+	Blog getPersonalBlog(Author author);
+
+	/**
+	 * Returns all blogs to which the user subscribes.
+	 */
+	Collection<Blog> getBlogs() throws DbException;
+
+	/**
+	 * Returns the header of the blog post with the given ID.
+	 */
+	BlogPostHeader getPostHeader(GroupId g, MessageId m) throws DbException;
+
+	/**
+	 * Returns the body of the blog post with the given ID.
+	 */
+	String getPostBody(MessageId m) throws DbException;
+
+	/**
+	 * Returns the headers of all posts in the given blog.
+	 */
+	Collection<BlogPostHeader> getPostHeaders(GroupId g) throws DbException;
+
+	/**
+	 * Marks a blog post as read or unread.
+	 */
+	void setReadFlag(MessageId m, boolean read) throws DbException;
+
+	/**
+	 * Registers a hook to be called whenever a blog is removed.
+	 */
+	void registerRemoveBlogHook(RemoveBlogHook hook);
+
+	interface RemoveBlogHook {
+		void removingBlog(Transaction txn, Blog b) throws DbException;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/BlogPost.java

@@ -0,0 +1,20 @@
+package org.briarproject.briar.api.blog;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.forum.ForumPost;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class BlogPost extends ForumPost {
+
+	public BlogPost(Message message, @Nullable MessageId parent,
+			Author author) {
+		super(message, parent, author);
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/BlogPostFactory.java

@@ -0,0 +1,54 @@
+package org.briarproject.briar.api.blog;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.identity.LocalAuthor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import java.security.GeneralSecurityException;
+
+import javax.annotation.Nullable;
+
+import static org.briarproject.briar.api.blog.BlogManager.CLIENT_ID;
+
+@NotNullByDefault
+public interface BlogPostFactory {
+
+	String SIGNING_LABEL_POST = CLIENT_ID + "/POST";
+	String SIGNING_LABEL_COMMENT = CLIENT_ID + "/COMMENT";
+
+	BlogPost createBlogPost(GroupId groupId, long timestamp,
+			@Nullable MessageId parent, LocalAuthor author, String body)
+			throws FormatException, GeneralSecurityException;
+
+	Message createBlogComment(GroupId groupId, LocalAuthor author,
+			@Nullable String comment, MessageId originalId, MessageId wrappedId)
+			throws FormatException, GeneralSecurityException;
+
+	/**
+	 * Wraps a blog post
+	 */
+	Message wrapPost(GroupId groupId, byte[] descriptor, long timestamp,
+			BdfList body) throws FormatException;
+
+	/**
+	 * Re-wraps a previously wrapped post
+	 */
+	Message rewrapWrappedPost(GroupId groupId, BdfList body)
+			throws FormatException;
+
+	/**
+	 * Wraps a blog comment
+	 */
+	Message wrapComment(GroupId groupId, byte[] descriptor, long timestamp,
+			BdfList body, MessageId currentId) throws FormatException;
+
+	/**
+	 * Re-wraps a previously wrapped comment
+	 */
+	Message rewrapWrappedComment(GroupId groupId, BdfList body,
+			MessageId currentId) throws FormatException;
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/BlogPostHeader.java

@@ -0,0 +1,48 @@
+package org.briarproject.briar.api.blog;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.identity.Author.Status;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.PostHeader;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class BlogPostHeader extends PostHeader {
+
+	private final MessageType type;
+	private final GroupId groupId;
+	private final long timeReceived;
+
+	public BlogPostHeader(MessageType type, GroupId groupId, MessageId id,
+			@Nullable MessageId parentId, long timestamp, long timeReceived,
+			Author author, Status authorStatus, boolean read) {
+		super(id, parentId, timestamp, author, authorStatus, read);
+		this.type = type;
+		this.groupId = groupId;
+		this.timeReceived = timeReceived;
+	}
+
+	public BlogPostHeader(MessageType type, GroupId groupId, MessageId id,
+			long timestamp, long timeReceived, Author author,
+			Status authorStatus, boolean read) {
+		this(type, groupId, id, null, timestamp, timeReceived, author,
+				authorStatus, read);
+	}
+
+	public MessageType getType() {
+		return type;
+	}
+
+	public GroupId getGroupId() {
+		return groupId;
+	}
+
+	public long getTimeReceived() {
+		return timeReceived;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/BlogSharingManager.java

@@ -0,0 +1,10 @@
+package org.briarproject.briar.api.blog;
+
+import org.briarproject.bramble.api.sync.ClientId;
+import org.briarproject.briar.api.sharing.SharingManager;
+
+public interface BlogSharingManager extends SharingManager<Blog> {
+
+	ClientId CLIENT_ID = new ClientId("org.briarproject.briar.blog.sharing");
+
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/BlogSharingMessage.java

@@ -0,0 +1,74 @@
+package org.briarproject.briar.api.blog;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.briar.api.client.SessionId;
+import org.briarproject.briar.api.sharing.SharingMessage.Invitation;
+
+import javax.annotation.Nullable;
+
+import static org.briarproject.briar.api.blog.BlogConstants.BLOG_AUTHOR_NAME;
+import static org.briarproject.briar.api.blog.BlogConstants.BLOG_PUBLIC_KEY;
+import static org.briarproject.briar.api.sharing.SharingConstants.INVITATION_MSG;
+import static org.briarproject.briar.api.sharing.SharingConstants.SESSION_ID;
+import static org.briarproject.briar.api.sharing.SharingConstants.TIME;
+
+@NotNullByDefault
+public interface BlogSharingMessage {
+
+	class BlogInvitation extends Invitation {
+
+		private final String blogAuthorName;
+		private final byte[] blogPublicKey;
+
+		public BlogInvitation(GroupId groupId, SessionId sessionId,
+				String blogAuthorName, byte[] blogPublicKey, long time,
+				@Nullable String message) {
+			super(groupId, sessionId, time, message);
+
+			this.blogAuthorName = blogAuthorName;
+			this.blogPublicKey = blogPublicKey;
+		}
+
+		@Override
+		public BdfList toBdfList() {
+			BdfList list = super.toBdfList();
+			list.add(BdfList.of(blogAuthorName, blogPublicKey));
+			if (message != null) list.add(message);
+			return list;
+		}
+
+		@Override
+		public BdfDictionary toBdfDictionary() {
+			BdfDictionary d = toBdfDictionaryHelper();
+			d.put(BLOG_AUTHOR_NAME, blogAuthorName);
+			d.put(BLOG_PUBLIC_KEY, blogPublicKey);
+			if (message != null) d.put(INVITATION_MSG, message);
+			return d;
+		}
+
+		public static BlogInvitation from(GroupId groupId, BdfDictionary d)
+				throws FormatException {
+
+			SessionId sessionId = new SessionId(d.getRaw(SESSION_ID));
+			String blogAuthorName = d.getString(BLOG_AUTHOR_NAME);
+			byte[] blogPublicKey = d.getRaw(BLOG_PUBLIC_KEY);
+			String message = d.getOptionalString(INVITATION_MSG);
+			long time = d.getLong(TIME);
+
+			return new BlogInvitation(groupId, sessionId, blogAuthorName,
+					blogPublicKey, time, message);
+		}
+
+		public String getBlogAuthorName() {
+			return blogAuthorName;
+		}
+
+		public byte[] getBlogPublicKey() {
+			return blogPublicKey;
+		}
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/MessageType.java

@@ -0,0 +1,34 @@
+package org.briarproject.briar.api.blog;
+
+public enum MessageType {
+
+	POST(0),
+	COMMENT(1),
+	WRAPPED_POST(2),
+	WRAPPED_COMMENT(3);
+
+	int value;
+
+	MessageType(int value) {
+		this.value = value;
+	}
+
+	public static MessageType valueOf(int value) {
+		switch (value) {
+			case 0:
+				return POST;
+			case 1:
+				return COMMENT;
+			case 2:
+				return WRAPPED_POST;
+			case 3:
+				return WRAPPED_COMMENT;
+			default:
+				throw new IllegalArgumentException();
+		}
+	}
+
+	public int getInt() {
+		return value;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/event/BlogInvitationRequestReceivedEvent.java

@@ -0,0 +1,21 @@
+package org.briarproject.briar.api.blog.event;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.blog.Blog;
+import org.briarproject.briar.api.sharing.InvitationRequest;
+import org.briarproject.briar.api.sharing.event.InvitationRequestReceivedEvent;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class BlogInvitationRequestReceivedEvent extends
+		InvitationRequestReceivedEvent<Blog> {
+
+	public BlogInvitationRequestReceivedEvent(Blog blog, ContactId contactId,
+			InvitationRequest request) {
+		super(blog, contactId, request);
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/event/BlogInvitationResponseReceivedEvent.java

@@ -0,0 +1,20 @@
+package org.briarproject.briar.api.blog.event;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.blog.BlogInvitationResponse;
+import org.briarproject.briar.api.sharing.event.InvitationResponseReceivedEvent;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class BlogInvitationResponseReceivedEvent
+		extends InvitationResponseReceivedEvent {
+
+	public BlogInvitationResponseReceivedEvent(ContactId contactId,
+			BlogInvitationResponse response) {
+		super(contactId, response);
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/blog/event/BlogPostAddedEvent.java

@@ -0,0 +1,40 @@
+package org.briarproject.briar.api.blog.event;
+
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.briar.api.blog.BlogPostHeader;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when a blog post is added to the database.
+ */
+@Immutable
+@NotNullByDefault
+public class BlogPostAddedEvent extends Event {
+
+	private final GroupId groupId;
+	private final BlogPostHeader header;
+	private final boolean local;
+
+	public BlogPostAddedEvent(GroupId groupId, BlogPostHeader header,
+			boolean local) {
+
+		this.groupId = groupId;
+		this.header = header;
+		this.local = local;
+	}
+
+	public GroupId getGroupId() {
+		return groupId;
+	}
+
+	public BlogPostHeader getHeader() {
+		return header;
+	}
+
+	public boolean isLocal() {
+		return local;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/client/BaseGroup.java

@@ -0,0 +1,38 @@
+package org.briarproject.briar.api.client;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.bramble.api.sync.GroupId;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public abstract class BaseGroup {
+
+	private final Group group;
+
+	public BaseGroup(Group group) {
+		this.group = group;
+	}
+
+	public GroupId getId() {
+		return group.getId();
+	}
+
+	public Group getGroup() {
+		return group;
+	}
+
+	@Override
+	public int hashCode() {
+		return group.hashCode();
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof BaseGroup &&
+				getGroup().equals(((BaseGroup) o).getGroup());
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/client/BaseMessageHeader.java

@@ -0,0 +1,58 @@
+package org.briarproject.briar.api.client;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public abstract class BaseMessageHeader {
+
+	private final MessageId id;
+	private final GroupId groupId;
+	private final long timestamp;
+	private final boolean local, read, sent, seen;
+
+	public BaseMessageHeader(MessageId id, GroupId groupId, long timestamp,
+			boolean local, boolean read, boolean sent, boolean seen) {
+
+		this.id = id;
+		this.groupId = groupId;
+		this.timestamp = timestamp;
+		this.local = local;
+		this.read = read;
+		this.sent = sent;
+		this.seen = seen;
+	}
+
+	public MessageId getId() {
+		return id;
+	}
+
+	public GroupId getGroupId() {
+		return groupId;
+	}
+
+	public long getTimestamp() {
+		return timestamp;
+	}
+
+	public boolean isLocal() {
+		return local;
+	}
+
+	public boolean isRead() {
+		return read;
+	}
+
+	public boolean isSent() {
+		return sent;
+	}
+
+	public boolean isSeen() {
+		return seen;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/client/MessageQueueManager.java

@@ -0,0 +1,72 @@
+package org.briarproject.briar.api.client;
+
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Metadata;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.ClientId;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.bramble.api.sync.InvalidMessageException;
+import org.briarproject.bramble.api.sync.MessageContext;
+
+@Deprecated
+@NotNullByDefault
+public interface MessageQueueManager {
+
+	/**
+	 * The key used for storing the queue's state in the group metadata.
+	 */
+	String QUEUE_STATE_KEY = "queueState";
+
+	/**
+	 * Sends a message using the given queue.
+	 */
+	QueueMessage sendMessage(Transaction txn, Group queue, long timestamp,
+			byte[] body, Metadata meta) throws DbException;
+
+	/**
+	 * Sets the message validator for the given client.
+	 */
+	void registerMessageValidator(ClientId c, QueueMessageValidator v);
+
+	/**
+	 * Sets the incoming message hook for the given client. The hook will be
+	 * called once for each incoming message that passes validation. Messages
+	 * are passed to the hook in order.
+	 */
+	void registerIncomingMessageHook(ClientId c, IncomingQueueMessageHook hook);
+
+	@Deprecated
+	interface QueueMessageValidator {
+
+		/**
+		 * Validates the given message and returns its metadata and
+		 * dependencies.
+		 */
+		MessageContext validateMessage(QueueMessage q, Group g)
+				throws InvalidMessageException;
+	}
+
+	@Deprecated
+	interface IncomingQueueMessageHook {
+
+		/**
+		 * Called once for each incoming message that passes validation.
+		 * Messages are passed to the hook in order.
+		 *
+		 * @throws DbException Should only be used for real database errors.
+		 * If this is thrown, delivery will be attempted again at next startup,
+		 * whereas if an InvalidMessageException is thrown,
+		 * the message will be permanently invalidated.
+		 * @throws InvalidMessageException for any non-database error
+		 * that occurs while handling remotely created data.
+		 * This includes errors that occur while handling locally created data
+		 * in a context controlled by remotely created data
+		 * (for example, parsing the metadata of a dependency
+		 * of an incoming message).
+		 * Never rethrow DbException as InvalidMessageException!
+		 */
+		void incomingMessage(Transaction txn, QueueMessage q, Metadata meta)
+				throws DbException, InvalidMessageException;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/client/MessageTracker.java

@@ -0,0 +1,70 @@
+package org.briarproject.briar.api.client;
+
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
+
+@NotNullByDefault
+public interface MessageTracker {
+
+	/**
+	 * Gets the number of visible and unread messages in the group
+	 * as well as the timestamp of the latest message
+	 **/
+	GroupCount getGroupCount(GroupId g) throws DbException;
+
+	/**
+	 * Gets the number of visible and unread messages in the group
+	 * as well as the timestamp of the latest message
+	 **/
+	GroupCount getGroupCount(Transaction txn, GroupId g) throws DbException;
+
+	/**
+	 * Updates the group count for the given incoming message.
+	 */
+	void trackIncomingMessage(Transaction txn, Message m) throws DbException;
+
+	/**
+	 * Updates the group count for the given outgoing message.
+	 */
+	void trackOutgoingMessage(Transaction txn, Message m) throws DbException;
+
+	/**
+	 * Updates the group count for the given message.
+	 */
+	void trackMessage(Transaction txn, GroupId g, long timestamp, boolean read)
+			throws DbException;
+
+	/**
+	 * Marks a message as read or unread and updates the group count.
+	 */
+	void setReadFlag(GroupId g, MessageId m, boolean read) throws DbException;
+
+	class GroupCount {
+
+		private final int msgCount, unreadCount;
+		private final long latestMsgTime;
+
+		public GroupCount(int msgCount, int unreadCount, long latestMsgTime) {
+			this.msgCount = msgCount;
+			this.unreadCount = unreadCount;
+			this.latestMsgTime = latestMsgTime;
+		}
+
+		public int getMsgCount() {
+			return msgCount;
+		}
+
+		public int getUnreadCount() {
+			return unreadCount;
+		}
+
+		public long getLatestMsgTime() {
+			return latestMsgTime;
+		}
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/client/MessageTree.java

@@ -0,0 +1,39 @@
+package org.briarproject.briar.api.client;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import java.util.Collection;
+import java.util.Comparator;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+public interface MessageTree<T extends MessageTree.MessageNode> {
+
+	void add(Collection<T> nodes);
+
+	void add(T node);
+
+	void setComparator(Comparator<T> comparator);
+
+	void clear();
+
+	Collection<T> depthFirstOrder();
+
+	@NotNullByDefault
+	interface MessageNode {
+
+		MessageId getId();
+
+		@Nullable
+		MessageId getParentId();
+
+		void setLevel(int level);
+
+		void setDescendantCount(int descendantCount);
+
+		long getTimestamp();
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/client/NamedGroup.java

@@ -0,0 +1,34 @@
+package org.briarproject.briar.api.client;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Group;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public abstract class NamedGroup extends BaseGroup {
+
+	private final String name;
+	private final byte[] salt;
+
+	public NamedGroup(Group group, String name, byte[] salt) {
+		super(group);
+		this.name = name;
+		this.salt = salt;
+	}
+
+	public String getName() {
+		return name;
+	}
+
+	public byte[] getSalt() {
+		return salt;
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof NamedGroup && super.equals(o);
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/client/PostHeader.java

@@ -0,0 +1,57 @@
+package org.briarproject.briar.api.client;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.identity.Author.Status;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public abstract class PostHeader {
+
+	private final MessageId id;
+	@Nullable
+	private final MessageId parentId;
+	private final long timestamp;
+	private final Author author;
+	private final Status authorStatus;
+	private final boolean read;
+
+	public PostHeader(MessageId id, @Nullable MessageId parentId,
+			long timestamp, Author author, Status authorStatus, boolean read) {
+		this.id = id;
+		this.parentId = parentId;
+		this.timestamp = timestamp;
+		this.author = author;
+		this.authorStatus = authorStatus;
+		this.read = read;
+	}
+
+	public MessageId getId() {
+		return id;
+	}
+
+	public Author getAuthor() {
+		return author;
+	}
+
+	public Status getAuthorStatus() {
+		return authorStatus;
+	}
+
+	public long getTimestamp() {
+		return timestamp;
+	}
+
+	public boolean isRead() {
+		return read;
+	}
+
+	@Nullable
+	public MessageId getParentId() {
+		return parentId;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/client/ProtocolEngine.java

@@ -0,0 +1,50 @@
+package org.briarproject.briar.api.client;
+
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.List;
+
+@Deprecated
+@NotNullByDefault
+public interface ProtocolEngine<A, S, M> {
+
+	StateUpdate<S, M> onLocalAction(S localState, A action);
+
+	StateUpdate<S, M> onMessageReceived(S localState, M received);
+
+	StateUpdate<S, M> onMessageDelivered(S localState, M delivered);
+
+	class StateUpdate<S, M> {
+		public final boolean deleteMessage;
+		public final boolean deleteState;
+		public final S localState;
+		public final List<M> toSend;
+		public final List<Event> toBroadcast;
+
+		/**
+		 * This class represents an update of the local protocol state.
+		 * It only shows how the state should be updated,
+		 * but does not carry out the updates on its own.
+		 *
+		 * @param deleteMessage whether to delete the message that triggered
+		 * the state update. This will be ignored for
+		 * {@link ProtocolEngine#onLocalAction}.
+		 * @param deleteState whether to delete the localState {@link S}
+		 * @param localState the new local state
+		 * @param toSend a list of messages to be sent as part of the
+		 * state update
+		 * @param toBroadcast a list of events to broadcast as result of the
+		 * state update
+		 */
+		public StateUpdate(boolean deleteMessage, boolean deleteState,
+				S localState, List<M> toSend, List<Event> toBroadcast) {
+
+			this.deleteMessage = deleteMessage;
+			this.deleteState = deleteState;
+			this.localState = localState;
+			this.toSend = toSend;
+			this.toBroadcast = toBroadcast;
+		}
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/client/ProtocolStateException.java

@@ -0,0 +1,12 @@
+package org.briarproject.briar.api.client;
+
+import org.briarproject.bramble.api.db.DbException;
+
+/**
+ * Thrown when a database operation is attempted as part of a protocol session
+ * and the operation is not applicable to the current protocol state. This
+ * exception may occur due to concurrent updates and does not indicate a
+ * database error.
+ */
+public class ProtocolStateException extends DbException {
+}

briar-api/src/main/java/org/briarproject/briar/api/client/QueueMessage.java

@@ -0,0 +1,31 @@
+package org.briarproject.briar.api.client;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
+import static org.briarproject.bramble.api.sync.SyncConstants.MESSAGE_HEADER_LENGTH;
+
+@Deprecated
+@NotNullByDefault
+public class QueueMessage extends Message {
+
+	public static final int QUEUE_MESSAGE_HEADER_LENGTH =
+			MESSAGE_HEADER_LENGTH + 8;
+	public static final int MAX_QUEUE_MESSAGE_BODY_LENGTH =
+			MAX_MESSAGE_BODY_LENGTH - 8;
+
+	private final long queuePosition;
+
+	public QueueMessage(MessageId id, GroupId groupId, long timestamp,
+			long queuePosition, byte[] raw) {
+		super(id, groupId, timestamp, raw);
+		this.queuePosition = queuePosition;
+	}
+
+	public long getQueuePosition() {
+		return queuePosition;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/client/QueueMessageFactory.java

@@ -0,0 +1,15 @@
+package org.briarproject.briar.api.client;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+
+@Deprecated
+@NotNullByDefault
+public interface QueueMessageFactory {
+
+	QueueMessage createMessage(GroupId groupId, long timestamp,
+			long queuePosition, byte[] body);
+
+	QueueMessage createMessage(MessageId id, byte[] raw);
+}

briar-api/src/main/java/org/briarproject/briar/api/client/SessionId.java

@@ -0,0 +1,24 @@
+package org.briarproject.briar.api.client;
+
+import org.briarproject.bramble.api.UniqueId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.ThreadSafe;
+
+/**
+ * Type-safe wrapper for a byte array that uniquely identifies a protocol
+ * session.
+ */
+@ThreadSafe
+@NotNullByDefault
+public class SessionId extends UniqueId {
+
+	public SessionId(byte[] id) {
+		super(id);
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof SessionId && super.equals(o);
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/client/ThreadedMessage.java

@@ -0,0 +1,36 @@
+package org.briarproject.briar.api.client;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.messaging.PrivateMessage;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public abstract class ThreadedMessage extends PrivateMessage {
+
+	@Nullable
+	private final MessageId parent;
+	private final Author author;
+
+	public ThreadedMessage(Message message, @Nullable MessageId parent,
+			Author author) {
+		super(message);
+		this.parent = parent;
+		this.author = author;
+	}
+
+	@Nullable
+	public MessageId getParent() {
+		return parent;
+	}
+
+	public Author getAuthor() {
+		return author;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/feed/Feed.java

@@ -0,0 +1,137 @@
+package org.briarproject.briar.api.feed;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfEntry;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+import static org.briarproject.briar.api.feed.FeedConstants.KEY_BLOG_GROUP_ID;
+import static org.briarproject.briar.api.feed.FeedConstants.KEY_FEED_ADDED;
+import static org.briarproject.briar.api.feed.FeedConstants.KEY_FEED_AUTHOR;
+import static org.briarproject.briar.api.feed.FeedConstants.KEY_FEED_DESC;
+import static org.briarproject.briar.api.feed.FeedConstants.KEY_FEED_LAST_ENTRY;
+import static org.briarproject.briar.api.feed.FeedConstants.KEY_FEED_TITLE;
+import static org.briarproject.briar.api.feed.FeedConstants.KEY_FEED_UPDATED;
+import static org.briarproject.briar.api.feed.FeedConstants.KEY_FEED_URL;
+
+@Immutable
+@NotNullByDefault
+public class Feed {
+
+	private final String url;
+	private final GroupId blogId;
+	@Nullable
+	private final String title, description, author;
+	private final long added, updated, lastEntryTime;
+
+	public Feed(String url, GroupId blogId, @Nullable String title,
+			@Nullable String description, @Nullable String author,
+			long added, long updated, long lastEntryTime) {
+
+		this.url = url;
+		this.blogId = blogId;
+		this.title = title;
+		this.description = description;
+		this.author = author;
+		this.added = added;
+		this.updated = updated;
+		this.lastEntryTime = lastEntryTime;
+	}
+
+	public Feed(String url, GroupId blogId, @Nullable String title,
+			@Nullable String description, @Nullable String author, long added) {
+		this(url, blogId, title, description, author, added, 0L, 0L);
+	}
+
+	public Feed(String url, GroupId blogId, long added) {
+		this(url, blogId, null, null, null, added, 0L, 0L);
+	}
+
+	public String getUrl() {
+		return url;
+	}
+
+	public GroupId getBlogId() {
+		return blogId;
+	}
+
+	public BdfDictionary toBdfDictionary() {
+		BdfDictionary d = BdfDictionary.of(
+				new BdfEntry(KEY_FEED_URL, url),
+				new BdfEntry(KEY_BLOG_GROUP_ID, blogId.getBytes()),
+				new BdfEntry(KEY_FEED_ADDED, added),
+				new BdfEntry(KEY_FEED_UPDATED, updated),
+				new BdfEntry(KEY_FEED_LAST_ENTRY, lastEntryTime)
+		);
+		if (title != null) d.put(KEY_FEED_TITLE, title);
+		if (description != null) d.put(KEY_FEED_DESC, description);
+		if (author != null) d.put(KEY_FEED_AUTHOR, author);
+		return d;
+	}
+
+	public static Feed from(BdfDictionary d) throws FormatException {
+		String url = d.getString(KEY_FEED_URL);
+		GroupId blogId = new GroupId(d.getRaw(KEY_BLOG_GROUP_ID));
+		String title = d.getOptionalString(KEY_FEED_TITLE);
+		String desc = d.getOptionalString(KEY_FEED_DESC);
+		String author = d.getOptionalString(KEY_FEED_AUTHOR);
+		long added = d.getLong(KEY_FEED_ADDED, 0L);
+		long updated = d.getLong(KEY_FEED_UPDATED, 0L);
+		long lastEntryTime = d.getLong(KEY_FEED_LAST_ENTRY, 0L);
+		return new Feed(url, blogId, title, desc, author, added, updated,
+				lastEntryTime);
+	}
+
+	@Nullable
+	public String getTitle() {
+		return title;
+	}
+
+	@Nullable
+	public String getDescription() {
+		return description;
+	}
+
+	@Nullable
+	public String getAuthor() {
+		return author;
+	}
+
+	public long getAdded() {
+		return added;
+	}
+
+	public long getUpdated() {
+		return updated;
+	}
+
+	public long getLastEntryTime() {
+		return lastEntryTime;
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (this == o) return true;
+		if (o instanceof Feed) {
+			Feed f = (Feed) o;
+			return url.equals(f.url) && blogId.equals(f.getBlogId()) &&
+					equalsWithNull(title, f.getTitle()) &&
+					equalsWithNull(description, f.getDescription()) &&
+					equalsWithNull(author, f.getAuthor()) &&
+					added == f.getAdded() &&
+					updated == f.getUpdated() &&
+					lastEntryTime == f.getLastEntryTime();
+		}
+		return false;
+	}
+
+	private boolean equalsWithNull(@Nullable Object a, @Nullable Object b) {
+		if (a == b) return true;
+		if (a == null || b == null) return false;
+		return a.equals(b);
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/feed/FeedConstants.java

@@ -0,0 +1,29 @@
+package org.briarproject.briar.api.feed;
+
+import java.util.concurrent.TimeUnit;
+
+import static java.util.concurrent.TimeUnit.MINUTES;
+
+public interface FeedConstants {
+
+	/* delay after start before fetching feed */
+	int FETCH_DELAY_INITIAL = 1;
+
+	/* the interval the feed should be fetched */
+	int FETCH_INTERVAL = 30;
+
+	/* the unit that applies to the fetch times */
+	TimeUnit FETCH_UNIT = MINUTES;
+
+	// group metadata keys
+	String KEY_FEEDS = "feeds";
+	String KEY_FEED_URL = "feedURL";
+	String KEY_BLOG_GROUP_ID = "blogGroupId";
+	String KEY_FEED_TITLE = "feedTitle";
+	String KEY_FEED_DESC = "feedDesc";
+	String KEY_FEED_AUTHOR = "feedAuthor";
+	String KEY_FEED_ADDED = "feedAdded";
+	String KEY_FEED_UPDATED = "feedUpdated";
+	String KEY_FEED_LAST_ENTRY = "feedLastEntryTime";
+
+}

briar-api/src/main/java/org/briarproject/briar/api/feed/FeedManager.java

@@ -0,0 +1,34 @@
+package org.briarproject.briar.api.feed;
+
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.ClientId;
+import org.briarproject.bramble.api.sync.GroupId;
+
+import java.io.IOException;
+import java.util.List;
+
+@NotNullByDefault
+public interface FeedManager {
+
+	/**
+	 * The unique ID of the RSS feed client.
+	 */
+	ClientId CLIENT_ID = new ClientId("org.briarproject.briar.feed");
+
+	/**
+	 * Adds an RSS feed.
+	 */
+	void addFeed(String url, GroupId g) throws DbException, IOException;
+
+	/**
+	 * Removes an RSS feed.
+	 */
+	void removeFeed(String url) throws DbException;
+
+	/**
+	 * Returns a list of all added RSS feeds
+	 */
+	List<Feed> getFeeds() throws DbException;
+
+}

briar-api/src/main/java/org/briarproject/briar/api/forum/Forum.java

@@ -0,0 +1,23 @@
+package org.briarproject.briar.api.forum;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.briar.api.client.NamedGroup;
+import org.briarproject.briar.api.sharing.Shareable;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class Forum extends NamedGroup implements Shareable {
+
+	public Forum(Group group, String name, byte[] salt) {
+		super(group, name, salt);
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof Forum && super.equals(o);
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/forum/ForumConstants.java

@@ -0,0 +1,40 @@
+package org.briarproject.briar.api.forum;
+
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
+
+public interface ForumConstants {
+
+	/**
+	 * The maximum length of a forum's name in UTF-8 bytes.
+	 */
+	int MAX_FORUM_NAME_LENGTH = 100;
+
+	/**
+	 * The length of a forum's random salt in bytes.
+	 */
+	int FORUM_SALT_LENGTH = 32;
+
+	/**
+	 * The maximum length of a forum post's content type in UTF-8 bytes.
+	 */
+	int MAX_CONTENT_TYPE_LENGTH = 50;
+
+	/**
+	 * The maximum length of a forum post's body in bytes.
+	 */
+	int MAX_FORUM_POST_BODY_LENGTH = MAX_MESSAGE_BODY_LENGTH - 1024;
+
+	/* Forum Sharing Constants */
+	String FORUM_NAME = "forumName";
+	String FORUM_SALT = "forumSalt";
+
+	// Database keys
+	String KEY_TIMESTAMP = "timestamp";
+	String KEY_PARENT = "parent";
+	String KEY_ID = "id";
+	String KEY_NAME = "name";
+	String KEY_PUBLIC_NAME = "publicKey";
+	String KEY_AUTHOR = "author";
+	String KEY_LOCAL = "local";
+
+}

briar-api/src/main/java/org/briarproject/briar/api/forum/ForumFactory.java

@@ -0,0 +1,18 @@
+package org.briarproject.briar.api.forum;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public interface ForumFactory {
+
+	/**
+	 * Creates a forum with the given name.
+	 */
+	Forum createForum(String name);
+
+	/**
+	 * Creates a forum with the given name and salt.
+	 */
+	Forum createForum(String name, byte[] salt);
+
+}

briar-api/src/main/java/org/briarproject/briar/api/forum/ForumInvitationRequest.java

@@ -0,0 +1,33 @@
+package org.briarproject.briar.api.forum;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.SessionId;
+import org.briarproject.briar.api.sharing.InvitationRequest;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class ForumInvitationRequest extends InvitationRequest {
+
+	private final String forumName;
+
+	public ForumInvitationRequest(MessageId id, SessionId sessionId,
+			GroupId groupId, ContactId contactId, String forumName,
+			@Nullable String message, boolean available, long time,
+			boolean local, boolean sent, boolean seen, boolean read) {
+
+		super(id, sessionId, groupId, contactId, message, available, time,
+				local, sent, seen, read);
+		this.forumName = forumName;
+	}
+
+	public String getForumName() {
+		return forumName;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/forum/ForumInvitationResponse.java

@@ -0,0 +1,24 @@
+package org.briarproject.briar.api.forum;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.SessionId;
+import org.briarproject.briar.api.sharing.InvitationResponse;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class ForumInvitationResponse extends InvitationResponse {
+
+	public ForumInvitationResponse(MessageId id, SessionId sessionId,
+			GroupId groupId, ContactId contactId, boolean accept, long time,
+			boolean local, boolean sent, boolean seen, boolean read) {
+
+		super(id, sessionId, groupId, contactId, accept, time, local, sent,
+				seen, read);
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/forum/ForumManager.java

@@ -0,0 +1,90 @@
+package org.briarproject.briar.api.forum;
+
+import org.briarproject.bramble.api.crypto.CryptoExecutor;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.identity.LocalAuthor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.ClientId;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.MessageTracker.GroupCount;
+
+import java.util.Collection;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+public interface ForumManager {
+
+	/**
+	 * The unique ID of the forum client.
+	 */
+	ClientId CLIENT_ID = new ClientId("org.briarproject.briar.forum");
+
+	/**
+	 * Subscribes to a forum.
+	 */
+	Forum addForum(String name) throws DbException;
+
+	/**
+	 * Unsubscribes from a forum.
+	 */
+	void removeForum(Forum f) throws DbException;
+
+	/**
+	 * Creates a local forum post.
+	 */
+	@CryptoExecutor
+	ForumPost createLocalPost(GroupId groupId, String body, long timestamp,
+			@Nullable MessageId parentId, LocalAuthor author);
+
+	/**
+	 * Stores a local forum post.
+	 */
+	ForumPostHeader addLocalPost(ForumPost p) throws DbException;
+
+	/**
+	 * Returns the forum with the given ID.
+	 */
+	Forum getForum(GroupId g) throws DbException;
+
+	/**
+	 * Returns the forum with the given ID.
+	 */
+	Forum getForum(Transaction txn, GroupId g) throws DbException;
+
+	/**
+	 * Returns all forums to which the user subscribes.
+	 */
+	Collection<Forum> getForums() throws DbException;
+
+	/**
+	 * Returns the body of the forum post with the given ID.
+	 */
+	String getPostBody(MessageId m) throws DbException;
+
+	/**
+	 * Returns the headers of all posts in the given forum.
+	 */
+	Collection<ForumPostHeader> getPostHeaders(GroupId g) throws DbException;
+
+	/**
+	 * Registers a hook to be called whenever a forum is removed.
+	 */
+	void registerRemoveForumHook(RemoveForumHook hook);
+
+	/**
+	 * Returns the group count for the given forum.
+	 */
+	GroupCount getGroupCount(GroupId g) throws DbException;
+
+	/**
+	 * Marks a message as read or unread and updates the group count.
+	 */
+	void setReadFlag(GroupId g, MessageId m, boolean read) throws DbException;
+
+	interface RemoveForumHook {
+		void removingForum(Transaction txn, Forum f) throws DbException;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/forum/ForumPost.java

@@ -0,0 +1,21 @@
+package org.briarproject.briar.api.forum;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.ThreadedMessage;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class ForumPost extends ThreadedMessage {
+
+	public ForumPost(Message message, @Nullable MessageId parent,
+			Author author) {
+		super(message, parent, author);
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/forum/ForumPostFactory.java

@@ -0,0 +1,26 @@
+package org.briarproject.briar.api.forum;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.crypto.CryptoExecutor;
+import org.briarproject.bramble.api.identity.LocalAuthor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import java.security.GeneralSecurityException;
+
+import javax.annotation.Nullable;
+
+import static org.briarproject.briar.api.forum.ForumManager.CLIENT_ID;
+
+@NotNullByDefault
+public interface ForumPostFactory {
+
+	String SIGNING_LABEL_POST = CLIENT_ID + "/POST";
+
+	@CryptoExecutor
+	ForumPost createPost(GroupId groupId, long timestamp,
+			@Nullable MessageId parent, LocalAuthor author, String body)
+			throws FormatException, GeneralSecurityException;
+
+}

briar-api/src/main/java/org/briarproject/briar/api/forum/ForumPostHeader.java

@@ -0,0 +1,21 @@
+package org.briarproject.briar.api.forum;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.PostHeader;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class ForumPostHeader extends PostHeader {
+
+	public ForumPostHeader(MessageId id, @Nullable MessageId parentId,
+			long timestamp, Author author, Author.Status authorStatus,
+			boolean read) {
+		super(id, parentId, timestamp, author, authorStatus, read);
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/forum/ForumSharingManager.java

@@ -0,0 +1,10 @@
+package org.briarproject.briar.api.forum;
+
+import org.briarproject.bramble.api.sync.ClientId;
+import org.briarproject.briar.api.sharing.SharingManager;
+
+public interface ForumSharingManager extends SharingManager<Forum> {
+
+	ClientId CLIENT_ID = new ClientId("org.briarproject.briar.forum.sharing");
+
+}

briar-api/src/main/java/org/briarproject/briar/api/forum/ForumSharingMessage.java

@@ -0,0 +1,79 @@
+package org.briarproject.briar.api.forum;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.briar.api.client.SessionId;
+import org.briarproject.briar.api.sharing.SharingMessage.Invitation;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+import static org.briarproject.briar.api.forum.ForumConstants.FORUM_NAME;
+import static org.briarproject.briar.api.forum.ForumConstants.FORUM_SALT;
+import static org.briarproject.briar.api.sharing.SharingConstants.INVITATION_MSG;
+import static org.briarproject.briar.api.sharing.SharingConstants.SESSION_ID;
+import static org.briarproject.briar.api.sharing.SharingConstants.TIME;
+
+@NotNullByDefault
+public interface ForumSharingMessage {
+
+	@Immutable
+	@NotNullByDefault
+	class ForumInvitation extends Invitation {
+
+		private final String forumName;
+		private final byte[] forumSalt;
+
+		public ForumInvitation(GroupId groupId, SessionId sessionId,
+				String forumName, byte[] forumSalt, long time,
+				@Nullable String message) {
+
+			super(groupId, sessionId, time, message);
+
+			this.forumName = forumName;
+			this.forumSalt = forumSalt;
+		}
+
+		@Override
+		public BdfList toBdfList() {
+			BdfList list = super.toBdfList();
+			list.add(forumName);
+			list.add(forumSalt);
+			if (message != null) list.add(message);
+			return list;
+		}
+
+		@Override
+		public BdfDictionary toBdfDictionary() {
+			BdfDictionary d = toBdfDictionaryHelper();
+			d.put(FORUM_NAME, forumName);
+			d.put(FORUM_SALT, forumSalt);
+			if (message != null) d.put(INVITATION_MSG, message);
+			return d;
+		}
+
+		public static ForumInvitation from(GroupId groupId, BdfDictionary d)
+				throws FormatException {
+
+			SessionId sessionId = new SessionId(d.getRaw(SESSION_ID));
+			String forumName = d.getString(FORUM_NAME);
+			byte[] forumSalt = d.getRaw(FORUM_SALT);
+			String message = d.getOptionalString(INVITATION_MSG);
+			long time = d.getLong(TIME);
+
+			return new ForumInvitation(groupId, sessionId, forumName, forumSalt,
+					time, message);
+		}
+
+		public String getForumName() {
+			return forumName;
+		}
+
+		public byte[] getForumSalt() {
+			return forumSalt;
+		}
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/forum/event/ForumInvitationRequestReceivedEvent.java

@@ -0,0 +1,21 @@
+package org.briarproject.briar.api.forum.event;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.forum.Forum;
+import org.briarproject.briar.api.forum.ForumInvitationRequest;
+import org.briarproject.briar.api.sharing.event.InvitationRequestReceivedEvent;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class ForumInvitationRequestReceivedEvent extends
+		InvitationRequestReceivedEvent<Forum> {
+
+	public ForumInvitationRequestReceivedEvent(Forum forum, ContactId contactId,
+			ForumInvitationRequest request) {
+		super(forum, contactId, request);
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/forum/event/ForumInvitationResponseReceivedEvent.java

@@ -0,0 +1,21 @@
+package org.briarproject.briar.api.forum.event;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.briar.api.forum.ForumInvitationResponse;
+import org.briarproject.briar.api.sharing.event.InvitationResponseReceivedEvent;
+
+public class ForumInvitationResponseReceivedEvent extends
+		InvitationResponseReceivedEvent {
+
+	private final String forumName;
+
+	public ForumInvitationResponseReceivedEvent(String forumName,
+			ContactId contactId, ForumInvitationResponse response) {
+		super(contactId, response);
+		this.forumName = forumName;
+	}
+
+	public String getForumName() {
+		return forumName;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/forum/event/ForumPostReceivedEvent.java

@@ -0,0 +1,34 @@
+package org.briarproject.briar.api.forum.event;
+
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.briar.api.forum.ForumPostHeader;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when a new forum post is received.
+ */
+@Immutable
+@NotNullByDefault
+public class ForumPostReceivedEvent extends Event {
+
+	private final ForumPostHeader forumPostHeader;
+	private final GroupId groupId;
+
+	public ForumPostReceivedEvent(ForumPostHeader forumPostHeader,
+			GroupId groupId) {
+
+		this.forumPostHeader = forumPostHeader;
+		this.groupId = groupId;
+	}
+
+	public ForumPostHeader getForumPostHeader() {
+		return forumPostHeader;
+	}
+
+	public GroupId getGroupId() {
+		return groupId;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/introduction/IntroduceeAction.java

@@ -0,0 +1,53 @@
+package org.briarproject.briar.api.introduction;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.Nullable;
+
+import static org.briarproject.briar.api.introduction.IntroductionConstants.TYPE_ABORT;
+import static org.briarproject.briar.api.introduction.IntroductionConstants.TYPE_ACK;
+import static org.briarproject.briar.api.introduction.IntroductionConstants.TYPE_REQUEST;
+import static org.briarproject.briar.api.introduction.IntroductionConstants.TYPE_RESPONSE;
+
+@NotNullByDefault
+public enum IntroduceeAction {
+
+	LOCAL_ACCEPT,
+	LOCAL_DECLINE,
+	LOCAL_ABORT,
+	REMOTE_REQUEST,
+	REMOTE_ACCEPT,
+	REMOTE_DECLINE,
+	REMOTE_ABORT,
+	ACK;
+
+	@Nullable
+	public static IntroduceeAction getRemote(int type, boolean accept) {
+		if (type == TYPE_REQUEST) return REMOTE_REQUEST;
+		if (type == TYPE_RESPONSE && accept) return REMOTE_ACCEPT;
+		if (type == TYPE_RESPONSE) return REMOTE_DECLINE;
+		if (type == TYPE_ACK) return ACK;
+		if (type == TYPE_ABORT) return REMOTE_ABORT;
+		return null;
+	}
+
+	@Nullable
+	public static IntroduceeAction getRemote(int type) {
+		return getRemote(type, true);
+	}
+
+	@Nullable
+	public static IntroduceeAction getLocal(int type, boolean accept) {
+		if (type == TYPE_RESPONSE && accept) return LOCAL_ACCEPT;
+		if (type == TYPE_RESPONSE) return LOCAL_DECLINE;
+		if (type == TYPE_ACK) return ACK;
+		if (type == TYPE_ABORT) return LOCAL_ABORT;
+		return null;
+	}
+
+	@Nullable
+	public static IntroduceeAction getLocal(int type) {
+		return getLocal(type, true);
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/introduction/IntroduceeProtocolState.java

@@ -0,0 +1,82 @@
+package org.briarproject.briar.api.introduction;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+import static org.briarproject.briar.api.introduction.IntroduceeAction.ACK;
+import static org.briarproject.briar.api.introduction.IntroduceeAction.LOCAL_ACCEPT;
+import static org.briarproject.briar.api.introduction.IntroduceeAction.LOCAL_DECLINE;
+import static org.briarproject.briar.api.introduction.IntroduceeAction.REMOTE_ACCEPT;
+import static org.briarproject.briar.api.introduction.IntroduceeAction.REMOTE_DECLINE;
+import static org.briarproject.briar.api.introduction.IntroduceeAction.REMOTE_REQUEST;
+
+@Immutable
+@NotNullByDefault
+public enum IntroduceeProtocolState {
+
+	ERROR(0),
+	AWAIT_REQUEST(1) {
+		@Override
+		public IntroduceeProtocolState next(IntroduceeAction a) {
+			if (a == REMOTE_REQUEST) return AWAIT_RESPONSES;
+			return ERROR;
+		}
+	},
+	AWAIT_RESPONSES(2) {
+		@Override
+		public IntroduceeProtocolState next(IntroduceeAction a) {
+			if (a == REMOTE_ACCEPT) return AWAIT_LOCAL_RESPONSE;
+			if (a == REMOTE_DECLINE) return FINISHED;
+			if (a == LOCAL_ACCEPT) return AWAIT_REMOTE_RESPONSE;
+			if (a == LOCAL_DECLINE) return FINISHED;
+			return ERROR;
+		}
+	},
+	AWAIT_REMOTE_RESPONSE(3) {
+		@Override
+		public IntroduceeProtocolState next(IntroduceeAction a) {
+			if (a == REMOTE_ACCEPT) return AWAIT_ACK;
+			if (a == REMOTE_DECLINE) return FINISHED;
+			return ERROR;
+		}
+	},
+	AWAIT_LOCAL_RESPONSE(4) {
+		@Override
+		public IntroduceeProtocolState next(IntroduceeAction a) {
+			if (a == LOCAL_ACCEPT) return AWAIT_ACK;
+			if (a == LOCAL_DECLINE) return FINISHED;
+			return ERROR;
+		}
+	},
+	AWAIT_ACK(5) {
+		@Override
+		public IntroduceeProtocolState next(IntroduceeAction a) {
+			if (a == ACK) return FINISHED;
+			return ERROR;
+		}
+	},
+	FINISHED(6);
+
+	private final int value;
+
+	IntroduceeProtocolState(int value) {
+		this.value = value;
+	}
+
+	public int getValue() {
+		return value;
+	}
+
+	public static IntroduceeProtocolState fromValue(int value) {
+		for (IntroduceeProtocolState s : values()) {
+			if (s.value == value) return s;
+		}
+		throw new IllegalArgumentException();
+	}
+
+	public IntroduceeProtocolState next(IntroduceeAction a) {
+		return this;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/introduction/IntroducerAction.java

@@ -0,0 +1,54 @@
+package org.briarproject.briar.api.introduction;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.Nullable;
+
+import static org.briarproject.briar.api.introduction.IntroductionConstants.TYPE_ABORT;
+import static org.briarproject.briar.api.introduction.IntroductionConstants.TYPE_ACK;
+import static org.briarproject.briar.api.introduction.IntroductionConstants.TYPE_REQUEST;
+import static org.briarproject.briar.api.introduction.IntroductionConstants.TYPE_RESPONSE;
+
+@NotNullByDefault
+public enum IntroducerAction {
+
+	LOCAL_REQUEST,
+	LOCAL_ABORT,
+	REMOTE_ACCEPT_1,
+	REMOTE_ACCEPT_2,
+	REMOTE_DECLINE_1,
+	REMOTE_DECLINE_2,
+	REMOTE_ABORT,
+	ACK_1,
+	ACK_2;
+
+	@Nullable
+	public static IntroducerAction getLocal(int type) {
+		if (type == TYPE_REQUEST) return LOCAL_REQUEST;
+		if (type == TYPE_ABORT) return LOCAL_ABORT;
+		return null;
+	}
+
+	@Nullable
+	public static IntroducerAction getRemote(int type, boolean one,
+			boolean accept) {
+
+		if (one) {
+			if (type == TYPE_RESPONSE && accept) return REMOTE_ACCEPT_1;
+			if (type == TYPE_RESPONSE) return REMOTE_DECLINE_1;
+			if (type == TYPE_ACK) return ACK_1;
+		} else {
+			if (type == TYPE_RESPONSE && accept) return REMOTE_ACCEPT_2;
+			if (type == TYPE_RESPONSE) return REMOTE_DECLINE_2;
+			if (type == TYPE_ACK) return ACK_2;
+		}
+		if (type == TYPE_ABORT) return REMOTE_ABORT;
+		return null;
+	}
+
+	@Nullable
+	public static IntroducerAction getRemote(int type, boolean one) {
+		return getRemote(type, one, true);
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/introduction/IntroducerProtocolState.java

@@ -0,0 +1,108 @@
+package org.briarproject.briar.api.introduction;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+import static org.briarproject.briar.api.introduction.IntroducerAction.ACK_1;
+import static org.briarproject.briar.api.introduction.IntroducerAction.ACK_2;
+import static org.briarproject.briar.api.introduction.IntroducerAction.LOCAL_REQUEST;
+import static org.briarproject.briar.api.introduction.IntroducerAction.REMOTE_ABORT;
+import static org.briarproject.briar.api.introduction.IntroducerAction.REMOTE_ACCEPT_1;
+import static org.briarproject.briar.api.introduction.IntroducerAction.REMOTE_ACCEPT_2;
+import static org.briarproject.briar.api.introduction.IntroducerAction.REMOTE_DECLINE_1;
+import static org.briarproject.briar.api.introduction.IntroducerAction.REMOTE_DECLINE_2;
+
+@Immutable
+@NotNullByDefault
+public enum IntroducerProtocolState {
+
+	ERROR(0),
+	PREPARE_REQUESTS(1) {
+		@Override
+		public IntroducerProtocolState next(IntroducerAction a) {
+			if (a == LOCAL_REQUEST) return AWAIT_RESPONSES;
+			return ERROR;
+		}
+	},
+	AWAIT_RESPONSES(2) {
+		@Override
+		public IntroducerProtocolState next(IntroducerAction a) {
+			if (a == REMOTE_ACCEPT_1) return AWAIT_RESPONSE_2;
+			if (a == REMOTE_ACCEPT_2) return AWAIT_RESPONSE_1;
+			if (a == REMOTE_DECLINE_1) return FINISHED;
+			if (a == REMOTE_DECLINE_2) return FINISHED;
+			return ERROR;
+		}
+	},
+	AWAIT_RESPONSE_1(3) {
+		@Override
+		public IntroducerProtocolState next(IntroducerAction a) {
+			if (a == REMOTE_ACCEPT_1) return AWAIT_ACKS;
+			if (a == REMOTE_DECLINE_1) return FINISHED;
+			return ERROR;
+		}
+	},
+	AWAIT_RESPONSE_2(4) {
+		@Override
+		public IntroducerProtocolState next(IntroducerAction a) {
+			if (a == REMOTE_ACCEPT_2) return AWAIT_ACKS;
+			if (a == REMOTE_DECLINE_2) return FINISHED;
+			return ERROR;
+		}
+	},
+	AWAIT_ACKS(5) {
+		@Override
+		public IntroducerProtocolState next(IntroducerAction a) {
+			if (a == ACK_1) return AWAIT_ACK_2;
+			if (a == ACK_2) return AWAIT_ACK_1;
+			return ERROR;
+		}
+	},
+	AWAIT_ACK_1(6) {
+		@Override
+		public IntroducerProtocolState next(IntroducerAction a) {
+			if (a == ACK_1) return FINISHED;
+			return ERROR;
+		}
+	},
+	AWAIT_ACK_2(7) {
+		@Override
+		public IntroducerProtocolState next(IntroducerAction a) {
+			if (a == ACK_2) return FINISHED;
+			return ERROR;
+		}
+	},
+	FINISHED(8) {
+		@Override
+		public IntroducerProtocolState next(IntroducerAction a) {
+			if (a == REMOTE_ABORT) return ERROR;
+			return FINISHED;
+		}
+	};
+
+	private final int value;
+
+	IntroducerProtocolState(int value) {
+		this.value = value;
+	}
+
+	public int getValue() {
+		return value;
+	}
+
+	public static IntroducerProtocolState fromValue(int value) {
+		for (IntroducerProtocolState s : values()) {
+			if (s.value == value) return s;
+		}
+		throw new IllegalArgumentException();
+	}
+
+	public static boolean isOngoing(IntroducerProtocolState state) {
+		return state != FINISHED && state != ERROR;
+	}
+
+	public IntroducerProtocolState next(IntroducerAction a) {
+		return this;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/introduction/IntroductionConstants.java

@@ -0,0 +1,89 @@
+package org.briarproject.briar.api.introduction;
+
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
+
+public interface IntroductionConstants {
+
+	/* Protocol roles */
+	int ROLE_INTRODUCER = 0;
+	int ROLE_INTRODUCEE = 1;
+
+	/* Message types */
+	int TYPE_REQUEST = 1;
+	int TYPE_RESPONSE = 2;
+	int TYPE_ACK = 3;
+	int TYPE_ABORT = 4;
+
+	/* Message Constants */
+	String TYPE = "type";
+	String GROUP_ID = "groupId";
+	String SESSION_ID = "sessionId";
+	String CONTACT = "contactId";
+	String NAME = "name";
+	String PUBLIC_KEY = "publicKey";
+	String E_PUBLIC_KEY = "ephemeralPublicKey";
+	String MSG = "msg";
+	String ACCEPT = "accept";
+	String TIME = "time";
+	String TRANSPORT = "transport";
+	String MESSAGE_ID = "messageId";
+	String MESSAGE_TIME = "timestamp";
+	String MAC = "mac";
+	String SIGNATURE = "signature";
+
+	/* Validation Constants */
+
+	/**
+	 * The length of the message authentication code in bytes.
+	 */
+	int MAC_LENGTH = 32;
+
+	/**
+	 * The maximum length of the introducer's optional message to the
+	 * introducees in UTF-8 bytes.
+	 */
+	int MAX_INTRODUCTION_MESSAGE_LENGTH = MAX_MESSAGE_BODY_LENGTH - 1024;
+
+	/* Introducer Local State Metadata */
+	String STATE = "state";
+	String ROLE = "role";
+	String GROUP_ID_1 = "groupId1";
+	String GROUP_ID_2 = "groupId2";
+	String CONTACT_1 = "contact1";
+	String CONTACT_2 = "contact2";
+	String AUTHOR_ID_1 = "authorId1";
+	String AUTHOR_ID_2 = "authorId2";
+	String CONTACT_ID_1 = "contactId1";
+	String CONTACT_ID_2 = "contactId2";
+	String RESPONSE_1 = "response1";
+	String RESPONSE_2 = "response2";
+
+	/* Introduction Request Action */
+	String PUBLIC_KEY1 = "publicKey1";
+	String PUBLIC_KEY2 = "publicKey2";
+
+	/* Introducee Local State Metadata (without those already defined) */
+	String STORAGE_ID = "storageId";
+	String INTRODUCER = "introducer";
+	String LOCAL_AUTHOR_ID = "localAuthorId";
+	String REMOTE_AUTHOR_ID = "remoteAuthorId";
+	String OUR_PUBLIC_KEY = "ourEphemeralPublicKey";
+	String OUR_PRIVATE_KEY = "ourEphemeralPrivateKey";
+	String OUR_TIME = "ourTime";
+	String ADDED_CONTACT_ID = "addedContactId";
+	String NOT_OUR_RESPONSE = "notOurResponse";
+	String EXISTS = "contactExists";
+	String REMOTE_AUTHOR_IS_US = "remoteAuthorIsUs";
+	String ANSWERED = "answered";
+	String NONCE = "nonce";
+	String MAC_KEY = "macKey";
+	String OUR_TRANSPORT = "ourTransport";
+	String OUR_MAC = "ourMac";
+	String OUR_SIGNATURE = "ourSignature";
+
+	String TASK = "task";
+	int TASK_ADD_CONTACT = 0;
+	int TASK_ACTIVATE_CONTACT = 1;
+	int TASK_ABORT = 2;
+
+}

briar-api/src/main/java/org/briarproject/briar/api/introduction/IntroductionManager.java

@@ -0,0 +1,50 @@
+package org.briarproject.briar.api.introduction;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.ClientId;
+import org.briarproject.briar.api.client.SessionId;
+import org.briarproject.briar.api.messaging.ConversationManager.ConversationClient;
+
+import java.util.Collection;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+public interface IntroductionManager extends ConversationClient {
+
+	/**
+	 * The unique ID of the introduction client.
+	 */
+	ClientId CLIENT_ID = new ClientId("org.briarproject.briar.introduction");
+
+	/**
+	 * Sends two initial introduction messages.
+	 */
+	void makeIntroduction(Contact c1, Contact c2, @Nullable String msg,
+			final long timestamp) throws DbException, FormatException;
+
+	/**
+	 * Accepts an introduction.
+	 */
+	void acceptIntroduction(final ContactId contactId,
+			final SessionId sessionId, final long timestamp)
+			throws DbException, FormatException;
+
+	/**
+	 * Declines an introduction.
+	 */
+	void declineIntroduction(final ContactId contactId,
+			final SessionId sessionId, final long timestamp)
+			throws DbException, FormatException;
+
+	/**
+	 * Returns all introduction messages for the given contact.
+	 */
+	Collection<IntroductionMessage> getIntroductionMessages(ContactId contactId)
+			throws DbException;
+
+}

briar-api/src/main/java/org/briarproject/briar/api/introduction/IntroductionMessage.java

@@ -0,0 +1,43 @@
+package org.briarproject.briar.api.introduction;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.BaseMessageHeader;
+import org.briarproject.briar.api.client.SessionId;
+
+import javax.annotation.concurrent.Immutable;
+
+import static org.briarproject.briar.api.introduction.IntroductionConstants.ROLE_INTRODUCER;
+
+@Immutable
+@NotNullByDefault
+public class IntroductionMessage extends BaseMessageHeader {
+
+	private final SessionId sessionId;
+	private final MessageId messageId;
+	private final int role;
+
+	IntroductionMessage(SessionId sessionId, MessageId messageId,
+			GroupId groupId, int role, long time, boolean local, boolean sent,
+			boolean seen, boolean read) {
+
+		super(messageId, groupId, time, local, read, sent, seen);
+		this.sessionId = sessionId;
+		this.messageId = messageId;
+		this.role = role;
+	}
+
+	public SessionId getSessionId() {
+		return sessionId;
+	}
+
+	public MessageId getMessageId() {
+		return messageId;
+	}
+
+	public boolean isIntroducer() {
+		return role == ROLE_INTRODUCER;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/introduction/IntroductionRequest.java

@@ -0,0 +1,51 @@
+package org.briarproject.briar.api.introduction;
+
+import org.briarproject.bramble.api.identity.AuthorId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.SessionId;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class IntroductionRequest extends IntroductionResponse {
+
+	@Nullable
+	private final String message;
+	private final boolean answered, exists, introducesOtherIdentity;
+
+	public IntroductionRequest(SessionId sessionId, MessageId messageId,
+			GroupId groupId, int role, long time, boolean local, boolean sent,
+			boolean seen, boolean read, AuthorId authorId, String name,
+			boolean accepted, @Nullable String message, boolean answered,
+			boolean exists, boolean introducesOtherIdentity) {
+
+		super(sessionId, messageId, groupId, role, time, local, sent, seen,
+				read, authorId, name, accepted);
+
+		this.message = message;
+		this.answered = answered;
+		this.exists = exists;
+		this.introducesOtherIdentity = introducesOtherIdentity;
+	}
+
+	@Nullable
+	public String getMessage() {
+		return message;
+	}
+
+	public boolean wasAnswered() {
+		return answered;
+	}
+
+	public boolean contactExists() {
+		return exists;
+	}
+
+	public boolean doesIntroduceOtherIdentity() {
+		return introducesOtherIdentity;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/introduction/IntroductionResponse.java

@@ -0,0 +1,43 @@
+package org.briarproject.briar.api.introduction;
+
+import org.briarproject.bramble.api.identity.AuthorId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.SessionId;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class IntroductionResponse extends IntroductionMessage {
+
+	private final AuthorId remoteAuthorId;
+	private final String name;
+	private final boolean accepted;
+
+	public IntroductionResponse(SessionId sessionId, MessageId messageId,
+			GroupId groupId, int role, long time, boolean local, boolean sent,
+			boolean seen, boolean read, AuthorId remoteAuthorId, String name,
+			boolean accepted) {
+
+		super(sessionId, messageId, groupId, role, time, local, sent, seen,
+				read);
+
+		this.remoteAuthorId = remoteAuthorId;
+		this.name = name;
+		this.accepted = accepted;
+	}
+
+	public String getName() {
+		return name;
+	}
+
+	public boolean wasAccepted() {
+		return accepted;
+	}
+
+	public AuthorId getRemoteAuthorId() {
+		return remoteAuthorId;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/introduction/event/IntroductionAbortedEvent.java

@@ -0,0 +1,29 @@
+package org.briarproject.briar.api.introduction.event;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.client.SessionId;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class IntroductionAbortedEvent extends Event {
+
+	private final ContactId contactId;
+	private final SessionId sessionId;
+
+	public IntroductionAbortedEvent(ContactId contactId, SessionId sessionId) {
+		this.contactId = contactId;
+		this.sessionId = sessionId;
+	}
+
+	public ContactId getContactId() {
+		return contactId;
+	}
+
+	public SessionId getSessionId() {
+		return sessionId;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/introduction/event/IntroductionRequestReceivedEvent.java

@@ -0,0 +1,32 @@
+package org.briarproject.briar.api.introduction.event;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.introduction.IntroductionRequest;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class IntroductionRequestReceivedEvent extends Event {
+
+	private final ContactId contactId;
+	private final IntroductionRequest introductionRequest;
+
+	public IntroductionRequestReceivedEvent(ContactId contactId,
+			IntroductionRequest introductionRequest) {
+
+		this.contactId = contactId;
+		this.introductionRequest = introductionRequest;
+	}
+
+	public ContactId getContactId() {
+		return contactId;
+	}
+
+	public IntroductionRequest getIntroductionRequest() {
+		return introductionRequest;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/introduction/event/IntroductionResponseReceivedEvent.java

@@ -0,0 +1,31 @@
+package org.briarproject.briar.api.introduction.event;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.introduction.IntroductionResponse;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class IntroductionResponseReceivedEvent extends Event {
+
+	private final ContactId contactId;
+	private final IntroductionResponse introductionResponse;
+
+	public IntroductionResponseReceivedEvent(ContactId contactId,
+			IntroductionResponse introductionResponse) {
+
+		this.contactId = contactId;
+		this.introductionResponse = introductionResponse;
+	}
+
+	public ContactId getContactId() {
+		return contactId;
+	}
+
+	public IntroductionResponse getIntroductionResponse() {
+		return introductionResponse;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/introduction/event/IntroductionSucceededEvent.java

@@ -0,0 +1,22 @@
+package org.briarproject.briar.api.introduction.event;
+
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class IntroductionSucceededEvent extends Event {
+
+	private final Contact contact;
+
+	public IntroductionSucceededEvent(Contact contact) {
+		this.contact = contact;
+	}
+
+	public Contact getContact() {
+		return contact;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/messaging/ConversationManager.java

@@ -0,0 +1,39 @@
+package org.briarproject.briar.api.messaging;
+
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.MessageTracker.GroupCount;
+
+@NotNullByDefault
+public interface ConversationManager {
+
+	/**
+	 * Clients that present messages in a private conversation need to
+	 * register themselves here.
+	 */
+	void registerConversationClient(ConversationClient client);
+
+	/**
+	 * Returns the unified group count for all private conversation messages.
+	 */
+	GroupCount getGroupCount(ContactId c) throws DbException;
+
+	@NotNullByDefault
+	interface ConversationClient {
+
+		Group getContactGroup(Contact c);
+
+		GroupCount getGroupCount(Transaction txn, ContactId c)
+				throws DbException;
+
+		void setReadFlag(GroupId g, MessageId m, boolean read)
+				throws DbException;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/messaging/MessagingConstants.java

@@ -0,0 +1,11 @@
+package org.briarproject.briar.api.messaging;
+
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
+
+public interface MessagingConstants {
+
+	/**
+	 * The maximum length of a private message's body in bytes.
+	 */
+	int MAX_PRIVATE_MESSAGE_BODY_LENGTH = MAX_MESSAGE_BODY_LENGTH - 1024;
+}

briar-api/src/main/java/org/briarproject/briar/api/messaging/MessagingManager.java

@@ -0,0 +1,47 @@
+package org.briarproject.briar.api.messaging;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.ClientId;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.messaging.ConversationManager.ConversationClient;
+
+import java.util.Collection;
+
+@NotNullByDefault
+public interface MessagingManager extends ConversationClient {
+
+	/**
+	 * The unique ID of the messaging client.
+	 */
+	ClientId CLIENT_ID = new ClientId("org.briarproject.briar.messaging");
+
+	/**
+	 * Stores a local private message.
+	 */
+	void addLocalMessage(PrivateMessage m) throws DbException;
+
+	/**
+	 * Returns the ID of the contact with the given private conversation.
+	 */
+	ContactId getContactId(GroupId g) throws DbException;
+
+	/**
+	 * Returns the ID of the private conversation with the given contact.
+	 */
+	GroupId getConversationId(ContactId c) throws DbException;
+
+	/**
+	 * Returns the headers of all messages in the given private conversation.
+	 */
+	Collection<PrivateMessageHeader> getMessageHeaders(ContactId c)
+			throws DbException;
+
+	/**
+	 * Returns the body of the private message with the given ID.
+	 */
+	String getMessageBody(MessageId m) throws DbException;
+
+}

briar-api/src/main/java/org/briarproject/briar/api/messaging/PrivateMessage.java

@@ -0,0 +1,22 @@
+package org.briarproject.briar.api.messaging;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Message;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class PrivateMessage {
+
+	private final Message message;
+
+	public PrivateMessage(Message message) {
+		this.message = message;
+	}
+
+	public Message getMessage() {
+		return message;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/messaging/PrivateMessageFactory.java

@@ -0,0 +1,13 @@
+package org.briarproject.briar.api.messaging;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+
+@NotNullByDefault
+public interface PrivateMessageFactory {
+
+	PrivateMessage createPrivateMessage(GroupId groupId, long timestamp,
+			String body) throws FormatException;
+
+}

briar-api/src/main/java/org/briarproject/briar/api/messaging/PrivateMessageHeader.java

@@ -0,0 +1,20 @@
+package org.briarproject.briar.api.messaging;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.BaseMessageHeader;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class PrivateMessageHeader extends BaseMessageHeader {
+
+	public PrivateMessageHeader(MessageId id, GroupId groupId, long timestamp,
+			boolean local, boolean read, boolean sent, boolean seen) {
+
+		super(id, groupId, timestamp, local, read, sent, seen);
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/messaging/event/PrivateMessageReceivedEvent.java

@@ -0,0 +1,40 @@
+package org.briarproject.briar.api.messaging.event;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.briar.api.messaging.PrivateMessageHeader;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when a new private message is received.
+ */
+@Immutable
+@NotNullByDefault
+public class PrivateMessageReceivedEvent extends Event {
+
+	private final PrivateMessageHeader messageHeader;
+	private final ContactId contactId;
+	private final GroupId groupId;
+
+	public PrivateMessageReceivedEvent(PrivateMessageHeader messageHeader,
+			ContactId contactId, GroupId groupId) {
+		this.messageHeader = messageHeader;
+		this.contactId = contactId;
+		this.groupId = groupId;
+	}
+
+	public PrivateMessageHeader getMessageHeader() {
+		return messageHeader;
+	}
+
+	public ContactId getContactId() {
+		return contactId;
+	}
+
+	public GroupId getGroupId() {
+		return groupId;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/GroupMember.java

@@ -0,0 +1,35 @@
+package org.briarproject.briar.api.privategroup;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.identity.Author.Status;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class GroupMember {
+
+	private final Author author;
+	private final Status status;
+	private final Visibility visibility;
+
+	public GroupMember(Author author, Status status, Visibility visibility) {
+		this.author = author;
+		this.status = status;
+		this.visibility = visibility;
+	}
+
+	public Author getAuthor() {
+		return author;
+	}
+
+	public Status getStatus() {
+		return status;
+	}
+
+	public Visibility getVisibility() {
+		return visibility;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/GroupMessage.java

@@ -0,0 +1,25 @@
+package org.briarproject.briar.api.privategroup;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.ThreadedMessage;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class GroupMessage extends ThreadedMessage {
+
+	public GroupMessage(Message message, @Nullable MessageId parent,
+			Author member) {
+		super(message, parent, member);
+	}
+
+	public Author getMember() {
+		return super.getAuthor();
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/GroupMessageFactory.java

@@ -0,0 +1,63 @@
+package org.briarproject.briar.api.privategroup;
+
+import org.briarproject.bramble.api.crypto.CryptoExecutor;
+import org.briarproject.bramble.api.identity.LocalAuthor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import javax.annotation.Nullable;
+
+import static org.briarproject.briar.api.privategroup.PrivateGroupManager.CLIENT_ID;
+
+@NotNullByDefault
+public interface GroupMessageFactory {
+
+	String SIGNING_LABEL_JOIN = CLIENT_ID + "/JOIN";
+	String SIGNING_LABEL_POST = CLIENT_ID + "/POST";
+
+	/**
+	 * Creates a join announcement message for the creator of a group.
+	 *
+	 * @param groupId The ID of the private group that is being joined
+	 * @param timestamp The timestamp to be used in the join announcement
+	 * @param creator The creator's identity
+	 */
+	@CryptoExecutor
+	GroupMessage createJoinMessage(GroupId groupId, long timestamp,
+			LocalAuthor creator);
+
+	/**
+	 * Creates a join announcement message for a joining member.
+	 *
+	 * @param groupId The ID of the private group that is being joined
+	 * @param timestamp The timestamp to be used in the join announcement,
+	 * which must be greater than the timestamp of the invitation message
+	 * @param member The member's identity
+	 * @param inviteTimestamp The timestamp of the invitation message
+	 * @param creatorSignature The creator's signature from the invitation
+	 * message
+	 */
+	@CryptoExecutor
+	GroupMessage createJoinMessage(GroupId groupId, long timestamp,
+			LocalAuthor member, long inviteTimestamp, byte[] creatorSignature);
+
+	/**
+	 * Creates a private group post.
+	 *
+	 * @param groupId The ID of the private group
+	 * @param timestamp Must be greater than the timestamps of the parent
+	 * post, if any, and the member's previous message
+	 * @param parentId The ID of the parent post, or null if the post has no
+	 * parent
+	 * @param author The author of the post
+	 * @param body The content of the post
+	 * @param previousMsgId The ID of the author's previous message
+	 * in this group
+	 */
+	@CryptoExecutor
+	GroupMessage createGroupMessage(GroupId groupId, long timestamp,
+			@Nullable MessageId parentId, LocalAuthor author, String body,
+			MessageId previousMsgId);
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/GroupMessageHeader.java

@@ -0,0 +1,30 @@
+package org.briarproject.briar.api.privategroup;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.identity.Author.Status;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.PostHeader;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class GroupMessageHeader extends PostHeader {
+
+	private final GroupId groupId;
+
+	public GroupMessageHeader(GroupId groupId, MessageId id,
+			@Nullable MessageId parentId, long timestamp,
+			Author author, Status authorStatus, boolean read) {
+		super(id, parentId, timestamp, author, authorStatus, read);
+		this.groupId = groupId;
+	}
+
+	public GroupId getGroupId() {
+		return groupId;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/JoinMessageHeader.java

@@ -0,0 +1,30 @@
+package org.briarproject.briar.api.privategroup;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class JoinMessageHeader extends GroupMessageHeader {
+
+	private final Visibility visibility;
+	private final boolean isInitial;
+
+	public JoinMessageHeader(GroupMessageHeader h, Visibility visibility,
+			boolean isInitial) {
+		super(h.getGroupId(), h.getId(), h.getParentId(), h.getTimestamp(),
+				h.getAuthor(), h.getAuthorStatus(), h.isRead());
+		this.visibility = visibility;
+		this.isInitial = isInitial;
+	}
+
+	public Visibility getVisibility() {
+		return visibility;
+	}
+
+	public boolean isInitial() {
+		return isInitial;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/MessageType.java

@@ -0,0 +1,28 @@
+package org.briarproject.briar.api.privategroup;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public enum MessageType {
+
+	JOIN(0),
+	POST(1);
+
+	private final int value;
+
+	MessageType(int value) {
+		this.value = value;
+	}
+
+	public static MessageType valueOf(int value) {
+		for (MessageType m : values()) if (m.value == value) return m;
+		throw new IllegalArgumentException();
+	}
+
+	public int getInt() {
+		return value;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/PrivateGroup.java

@@ -0,0 +1,31 @@
+package org.briarproject.briar.api.privategroup;
+
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.briar.api.client.NamedGroup;
+import org.briarproject.briar.api.sharing.Shareable;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class PrivateGroup extends NamedGroup implements Shareable {
+
+	private final Author creator;
+
+	public PrivateGroup(Group group, String name, Author creator, byte[] salt) {
+		super(group, name, salt);
+		this.creator = creator;
+	}
+
+	public Author getCreator() {
+		return creator;
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof PrivateGroup && super.equals(o);
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/PrivateGroupConstants.java

@@ -0,0 +1,27 @@
+package org.briarproject.briar.api.privategroup;
+
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
+
+public interface PrivateGroupConstants {
+
+	/**
+	 * The maximum length of a group's name in UTF-8 bytes.
+	 */
+	int MAX_GROUP_NAME_LENGTH = 100;
+
+	/**
+	 * The length of a group's random salt in bytes.
+	 */
+	int GROUP_SALT_LENGTH = 32;
+
+	/**
+	 * The maximum length of a group post's body in bytes.
+	 */
+	int MAX_GROUP_POST_BODY_LENGTH = MAX_MESSAGE_BODY_LENGTH - 1024;
+
+	/**
+	 * The maximum length of a group invitation message in bytes.
+	 */
+	int MAX_GROUP_INVITATION_MSG_LENGTH = MAX_MESSAGE_BODY_LENGTH - 1024;
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/PrivateGroupFactory.java

@@ -0,0 +1,26 @@
+package org.briarproject.briar.api.privategroup;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Group;
+
+@NotNullByDefault
+public interface PrivateGroupFactory {
+
+	/**
+	 * Creates a private group with the given name and author.
+	 */
+	PrivateGroup createPrivateGroup(String name, Author author);
+
+	/**
+	 * Creates a private group with the given name, author and salt.
+	 */
+	PrivateGroup createPrivateGroup(String name, Author author, byte[] salt);
+
+	/**
+	 * Parses a group and returns the corresponding PrivateGroup.
+	 */
+	PrivateGroup parsePrivateGroup(Group group) throws FormatException;
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/PrivateGroupManager.java

@@ -0,0 +1,140 @@
+package org.briarproject.briar.api.privategroup;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.identity.AuthorId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.ClientId;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.MessageTracker.GroupCount;
+
+import java.util.Collection;
+
+@NotNullByDefault
+public interface PrivateGroupManager {
+
+	/**
+	 * The unique ID of the private group client.
+	 */
+	ClientId CLIENT_ID = new ClientId("org.briarproject.briar.privategroup");
+
+	/**
+	 * Adds a new private group and joins it.
+	 *
+	 * @param group The private group to add
+	 * @param joinMsg The new member's join message
+	 * @param creator True if the group is added by its creator
+	 */
+	void addPrivateGroup(PrivateGroup group, GroupMessage joinMsg,
+			boolean creator) throws DbException;
+
+	/**
+	 * Adds a new private group and joins it.
+	 *
+	 * @param group The private group to add
+	 * @param joinMsg The new member's join message
+	 * @param creator True if the group is added by its creator
+	 */
+	void addPrivateGroup(Transaction txn, PrivateGroup group,
+			GroupMessage joinMsg, boolean creator) throws DbException;
+
+	/**
+	 * Removes a dissolved private group.
+	 */
+	void removePrivateGroup(GroupId g) throws DbException;
+
+	/**
+	 * Returns the ID of the user's previous message sent to the group
+	 */
+	MessageId getPreviousMsgId(GroupId g) throws DbException;
+
+	/**
+	 * Marks the given private group as dissolved.
+	 */
+	void markGroupDissolved(Transaction txn, GroupId g) throws DbException;
+
+	/**
+	 * Returns true if the given private group has been dissolved.
+	 */
+	boolean isDissolved(GroupId g) throws DbException;
+
+	/**
+	 * Stores and sends a local private group message.
+	 */
+	GroupMessageHeader addLocalMessage(GroupMessage p) throws DbException;
+
+	/**
+	 * Returns the private group with the given ID.
+	 */
+	PrivateGroup getPrivateGroup(GroupId g) throws DbException;
+
+	/**
+	 * Returns the private group with the given ID.
+	 */
+	PrivateGroup getPrivateGroup(Transaction txn, GroupId g) throws DbException;
+
+	/**
+	 * Returns all private groups the user is a member of.
+	 */
+	Collection<PrivateGroup> getPrivateGroups() throws DbException;
+
+	/**
+	 * Returns the body of the private group message with the given ID.
+	 */
+	String getMessageBody(MessageId m) throws DbException;
+
+	/**
+	 * Returns the headers of all messages in the given private group.
+	 */
+	Collection<GroupMessageHeader> getHeaders(GroupId g) throws DbException;
+
+	/**
+	 * Returns all members of the given private group.
+	 */
+	Collection<GroupMember> getMembers(GroupId g) throws DbException;
+
+	/**
+	 * Returns true if the given author is a member of the given private group.
+	 */
+	boolean isMember(Transaction txn, GroupId g, Author a) throws DbException;
+
+	/**
+	 * Returns the group count for the given private group.
+	 */
+	GroupCount getGroupCount(GroupId g) throws DbException;
+
+	/**
+	 * Marks a message as read or unread and updates the group count.
+	 */
+	void setReadFlag(GroupId g, MessageId m, boolean read) throws DbException;
+
+	/**
+	 * Called when a contact relationship has been revealed between the user
+	 * and the given author in the given private group.
+	 *
+	 * @param byContact True if the contact revealed the relationship first,
+	 * otherwise false.
+	 */
+	void relationshipRevealed(Transaction txn, GroupId g, AuthorId a,
+			boolean byContact) throws FormatException, DbException;
+
+	/**
+	 * Registers a hook to be called when members are added or private groups
+	 * are removed.
+	 */
+	void registerPrivateGroupHook(PrivateGroupHook hook);
+
+	@NotNullByDefault
+	interface PrivateGroupHook {
+
+		void addingMember(Transaction txn, GroupId g, Author a)
+				throws DbException;
+
+		void removingGroup(Transaction txn, GroupId g) throws DbException;
+
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/Visibility.java

@@ -0,0 +1,32 @@
+package org.briarproject.briar.api.privategroup;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public enum Visibility {
+
+	INVISIBLE(0),
+	VISIBLE(1),
+	REVEALED_BY_US(2),
+	REVEALED_BY_CONTACT(3);
+
+	private final int value;
+
+	Visibility(int value) {
+		this.value = value;
+	}
+
+	public static Visibility valueOf(int value) throws FormatException {
+		for (Visibility v : values()) if (v.value == value) return v;
+		throw new FormatException();
+	}
+
+	public int getInt() {
+		return value;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/event/ContactRelationshipRevealedEvent.java

@@ -0,0 +1,38 @@
+package org.briarproject.briar.api.privategroup.event;
+
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.identity.AuthorId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.briar.api.privategroup.Visibility;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class ContactRelationshipRevealedEvent extends Event {
+
+	private final GroupId groupId;
+	private final AuthorId memberId;
+	private final Visibility visibility;
+
+	public ContactRelationshipRevealedEvent(GroupId groupId, AuthorId memberId,
+			Visibility visibility) {
+		this.groupId = groupId;
+		this.memberId = memberId;
+		this.visibility = visibility;
+	}
+
+	public GroupId getGroupId() {
+		return groupId;
+	}
+
+	public AuthorId getMemberId() {
+		return memberId;
+	}
+
+	public Visibility getVisibility() {
+		return visibility;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/event/GroupDissolvedEvent.java

@@ -0,0 +1,27 @@
+package org.briarproject.briar.api.privategroup.event;
+
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when a private group is dissolved by a remote
+ * creator.
+ */
+@Immutable
+@NotNullByDefault
+public class GroupDissolvedEvent extends Event {
+
+	private final GroupId groupId;
+
+	public GroupDissolvedEvent(GroupId groupId) {
+		this.groupId = groupId;
+	}
+
+	public GroupId getGroupId() {
+		return groupId;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/event/GroupInvitationRequestReceivedEvent.java

@@ -0,0 +1,21 @@
+package org.briarproject.briar.api.privategroup.event;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.privategroup.PrivateGroup;
+import org.briarproject.briar.api.privategroup.invitation.GroupInvitationRequest;
+import org.briarproject.briar.api.sharing.event.InvitationRequestReceivedEvent;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class GroupInvitationRequestReceivedEvent extends
+		InvitationRequestReceivedEvent<PrivateGroup> {
+
+	public GroupInvitationRequestReceivedEvent(PrivateGroup group,
+			ContactId contactId, GroupInvitationRequest request) {
+		super(group, contactId, request);
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/event/GroupInvitationResponseReceivedEvent.java

@@ -0,0 +1,19 @@
+package org.briarproject.briar.api.privategroup.event;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.sharing.InvitationResponse;
+import org.briarproject.briar.api.sharing.event.InvitationResponseReceivedEvent;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class GroupInvitationResponseReceivedEvent
+		extends InvitationResponseReceivedEvent {
+
+	public GroupInvitationResponseReceivedEvent(ContactId contactId,
+			InvitationResponse response) {
+		super(contactId, response);
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/event/GroupMessageAddedEvent.java

@@ -0,0 +1,42 @@
+package org.briarproject.briar.api.privategroup.event;
+
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.briar.api.privategroup.GroupMessageHeader;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when a private group message was added
+ * to the database.
+ */
+@Immutable
+@NotNullByDefault
+public class GroupMessageAddedEvent extends Event {
+
+	private final GroupId groupId;
+	private final GroupMessageHeader header;
+	private final boolean local;
+
+	public GroupMessageAddedEvent(GroupId groupId, GroupMessageHeader header,
+			boolean local) {
+
+		this.groupId = groupId;
+		this.header = header;
+		this.local = local;
+	}
+
+	public GroupId getGroupId() {
+		return groupId;
+	}
+
+	public GroupMessageHeader getHeader() {
+		return header;
+	}
+
+	public boolean isLocal() {
+		return local;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/invitation/GroupInvitationFactory.java

@@ -0,0 +1,34 @@
+package org.briarproject.briar.api.privategroup.invitation;
+
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.crypto.CryptoExecutor;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.identity.AuthorId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+
+import static org.briarproject.briar.api.privategroup.invitation.GroupInvitationManager.CLIENT_ID;
+
+@NotNullByDefault
+public interface GroupInvitationFactory {
+
+	String SIGNING_LABEL_INVITE = CLIENT_ID + "/INVITE";
+
+	/**
+	 * Returns a signature to include when inviting a member to join a private
+	 * group. If the member accepts the invitation, the signature will be
+	 * included in the member's join message.
+	 */
+	@CryptoExecutor
+	byte[] signInvitation(Contact c, GroupId privateGroupId, long timestamp,
+			byte[] privateKey);
+
+	/**
+	 * Returns a token to be signed by the creator when inviting a member to
+	 * join a private group. If the member accepts the invitation, the
+	 * signature will be included in the member's join message.
+	 */
+	BdfList createInviteToken(AuthorId creatorId, AuthorId memberId,
+			GroupId privateGroupId, long timestamp);
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/invitation/GroupInvitationItem.java

@@ -0,0 +1,25 @@
+package org.briarproject.briar.api.privategroup.invitation;
+
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.privategroup.PrivateGroup;
+import org.briarproject.briar.api.sharing.InvitationItem;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class GroupInvitationItem extends InvitationItem<PrivateGroup> {
+
+	private final Contact creator;
+
+	public GroupInvitationItem(PrivateGroup privateGroup, Contact creator) {
+		super(privateGroup, false);
+		this.creator = creator;
+	}
+
+	public Contact getCreator() {
+		return creator;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/invitation/GroupInvitationManager.java

@@ -0,0 +1,83 @@
+package org.briarproject.briar.api.privategroup.invitation;
+
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.ClientId;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.briar.api.client.ProtocolStateException;
+import org.briarproject.briar.api.client.SessionId;
+import org.briarproject.briar.api.messaging.ConversationManager.ConversationClient;
+import org.briarproject.briar.api.privategroup.PrivateGroup;
+import org.briarproject.briar.api.sharing.InvitationMessage;
+
+import java.util.Collection;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+public interface GroupInvitationManager extends ConversationClient {
+
+	/**
+	 * The unique ID of the private group invitation client.
+	 */
+	ClientId CLIENT_ID =
+			new ClientId("org.briarproject.briar.privategroup.invitation");
+
+	/**
+	 * Sends an invitation to share the given private group with the given
+	 * contact, including an optional message.
+	 *
+	 * @throws ProtocolStateException if the group is no longer eligible to be
+	 * shared with the contact, for example because an invitation is already
+	 * pending.
+	 */
+	void sendInvitation(GroupId g, ContactId c, @Nullable String message,
+			long timestamp, byte[] signature) throws DbException;
+
+	/**
+	 * Responds to a pending private group invitation from the given contact.
+	 *
+	 * @throws ProtocolStateException if the invitation is no longer pending,
+	 * for example because the group has been dissolved.
+	 */
+	void respondToInvitation(ContactId c, PrivateGroup g, boolean accept)
+			throws DbException;
+
+	/**
+	 * Responds to a pending private group invitation from the given contact.
+	 *
+	 * @throws ProtocolStateException if the invitation is no longer pending,
+	 * for example because the group has been dissolved.
+	 */
+	void respondToInvitation(ContactId c, SessionId s, boolean accept)
+			throws DbException;
+
+	/**
+	 * Makes the user's relationship with the given contact visible to the
+	 * given private group.
+	 *
+	 * @throws ProtocolStateException if the relationship is no longer eligible
+	 * to be revealed, for example because the contact has revealed it.
+	 */
+	void revealRelationship(ContactId c, GroupId g) throws DbException;
+
+	/**
+	 * Returns all private group invitation messages related to the given
+	 * contact.
+	 */
+	Collection<InvitationMessage> getInvitationMessages(ContactId c)
+			throws DbException;
+
+	/**
+	 * Returns all private groups to which the user has been invited.
+	 */
+	Collection<GroupInvitationItem> getInvitations() throws DbException;
+
+	/**
+	 * Returns true if the given contact can be invited to the given private
+	 * group.
+	 */
+	boolean isInvitationAllowed(Contact c, GroupId g) throws DbException;
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/invitation/GroupInvitationRequest.java

@@ -0,0 +1,39 @@
+package org.briarproject.briar.api.privategroup.invitation;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.SessionId;
+import org.briarproject.briar.api.sharing.InvitationRequest;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class GroupInvitationRequest extends InvitationRequest {
+
+	private final String groupName;
+	private final Author creator;
+
+	public GroupInvitationRequest(MessageId id, SessionId sessionId,
+			GroupId groupId, ContactId contactId, @Nullable String message,
+			String groupName, Author creator, boolean available, long time,
+			boolean local, boolean sent, boolean seen, boolean read) {
+		super(id, sessionId, groupId, contactId, message, available, time,
+				local, sent, seen, read);
+		this.groupName = groupName;
+		this.creator = creator;
+	}
+
+	public String getGroupName() {
+		return groupName;
+	}
+
+	public Author getCreator() {
+		return creator;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/invitation/GroupInvitationResponse.java

@@ -0,0 +1,22 @@
+package org.briarproject.briar.api.privategroup.invitation;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.SessionId;
+import org.briarproject.briar.api.sharing.InvitationResponse;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class GroupInvitationResponse extends InvitationResponse {
+
+	public GroupInvitationResponse(MessageId id, SessionId sessionId,
+			GroupId groupId, ContactId contactId, boolean accept, long time,
+			boolean local, boolean sent, boolean seen, boolean read) {
+		super(id, sessionId, groupId, contactId, accept, time, local, sent,
+				seen, read);
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/sharing/InvitationFactory.java

@@ -0,0 +1,10 @@
+package org.briarproject.briar.api.sharing;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.sync.GroupId;
+
+public interface InvitationFactory<I extends SharingMessage.Invitation> {
+
+	I build(GroupId groupId, BdfDictionary d) throws FormatException;
+}

briar-api/src/main/java/org/briarproject/briar/api/sharing/InvitationItem.java

@@ -0,0 +1,36 @@
+package org.briarproject.briar.api.sharing;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public abstract class InvitationItem<S extends Shareable> {
+
+	private final S shareable;
+	private final boolean subscribed;
+
+	public InvitationItem(S shareable, boolean subscribed) {
+		this.shareable = shareable;
+		this.subscribed = subscribed;
+	}
+
+	public S getShareable() {
+		return shareable;
+	}
+
+	public GroupId getId() {
+		return shareable.getId();
+	}
+
+	public String getName() {
+		return shareable.getName();
+	}
+
+	public boolean isSubscribed() {
+		return subscribed;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/sharing/InvitationMessage.java

@@ -0,0 +1,36 @@
+package org.briarproject.briar.api.sharing;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.BaseMessageHeader;
+import org.briarproject.briar.api.client.SessionId;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public abstract class InvitationMessage extends BaseMessageHeader {
+
+	private final SessionId sessionId;
+	private final ContactId contactId;
+
+	public InvitationMessage(MessageId id, SessionId sessionId, GroupId groupId,
+			ContactId contactId, long time, boolean local, boolean sent,
+			boolean seen, boolean read) {
+
+		super(id, groupId, time, local, read, sent, seen);
+		this.sessionId = sessionId;
+		this.contactId = contactId;
+	}
+
+	public SessionId getSessionId() {
+		return sessionId;
+	}
+
+	public ContactId getContactId() {
+		return contactId;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/sharing/InvitationRequest.java

@@ -0,0 +1,39 @@
+package org.briarproject.briar.api.sharing;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.SessionId;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public abstract class InvitationRequest extends InvitationMessage {
+
+	@Nullable
+	private final String message;
+	private final boolean available;
+
+	public InvitationRequest(MessageId id, SessionId sessionId, GroupId groupId,
+			ContactId contactId, @Nullable String message, boolean available,
+			long time, boolean local, boolean sent, boolean seen,
+			boolean read) {
+
+		super(id, sessionId, groupId, contactId, time, local, sent, seen, read);
+		this.message = message;
+		this.available = available;
+	}
+
+	@Nullable
+	public String getMessage() {
+		return message;
+	}
+
+	public boolean isAvailable() {
+		return available;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/sharing/InvitationResponse.java

@@ -0,0 +1,28 @@
+package org.briarproject.briar.api.sharing;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.SessionId;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public abstract class InvitationResponse extends InvitationMessage {
+
+	private final boolean accept;
+
+	public InvitationResponse(MessageId id, SessionId sessionId,
+			GroupId groupId, ContactId contactId, boolean accept, long time,
+			boolean local, boolean sent, boolean seen, boolean read) {
+
+		super(id, sessionId, groupId, contactId, time, local, sent, seen, read);
+		this.accept = accept;
+	}
+
+	public boolean wasAccepted() {
+		return accept;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/sharing/Shareable.java

@@ -0,0 +1,16 @@
+package org.briarproject.briar.api.sharing;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.bramble.api.sync.GroupId;
+
+@NotNullByDefault
+public interface Shareable {
+
+	GroupId getId();
+
+	Group getGroup();
+
+	String getName();
+
+}

briar-api/src/main/java/org/briarproject/briar/api/sharing/SharingConstants.java

@@ -0,0 +1,48 @@
+package org.briarproject.briar.api.sharing;
+
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
+
+public interface SharingConstants {
+
+	/**
+	 * The length of a sharing session's random salt in bytes.
+	 */
+	int SHARING_SALT_LENGTH = 32;
+
+	/**
+	 * The maximum length of the optional message from the inviter to the
+	 * invitee in UTF-8 bytes.
+	 */
+	int MAX_INVITATION_MESSAGE_LENGTH = MAX_MESSAGE_BODY_LENGTH - 1024;
+
+	String CONTACT_ID = "contactId";
+	String GROUP_ID = "groupId";
+	String TO_BE_SHARED_BY_US = "toBeSharedByUs";
+	String SHARED_BY_US = "sharedByUs";
+	String SHARED_WITH_US = "sharedWithUs";
+	String TYPE = "type";
+	String SESSION_ID = "sessionId";
+	String STORAGE_ID = "storageId";
+	String STATE = "state";
+	String LOCAL = "local";
+	String TIME = "time";
+	String IS_SHARER = "isSharer";
+	String SHAREABLE_ID = "shareableId";
+	String INVITATION_MSG = "invitationMsg";
+	String INVITATION_ID = "invitationId";
+	String RESPONSE_ID = "responseId";
+	int SHARE_MSG_TYPE_INVITATION = 1;
+	int SHARE_MSG_TYPE_ACCEPT = 2;
+	int SHARE_MSG_TYPE_DECLINE = 3;
+	int SHARE_MSG_TYPE_LEAVE = 4;
+	int SHARE_MSG_TYPE_ABORT = 5;
+	int TASK_ADD_SHAREABLE_TO_LIST_SHARED_WITH_US = 0;
+	int TASK_REMOVE_SHAREABLE_FROM_LIST_SHARED_WITH_US = 1;
+	int TASK_ADD_SHARED_SHAREABLE = 2;
+	int TASK_ADD_SHAREABLE_TO_LIST_TO_BE_SHARED_BY_US = 3;
+	int TASK_REMOVE_SHAREABLE_FROM_LIST_TO_BE_SHARED_BY_US = 4;
+	int TASK_SHARE_SHAREABLE = 5;
+	int TASK_UNSHARE_SHAREABLE_SHARED_BY_US = 6;
+	int TASK_UNSHARE_SHAREABLE_SHARED_WITH_US = 7;
+
+}

briar-api/src/main/java/org/briarproject/briar/api/sharing/SharingInvitationItem.java

@@ -0,0 +1,27 @@
+package org.briarproject.briar.api.sharing;
+
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.Collection;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class SharingInvitationItem extends InvitationItem<Shareable> {
+
+	private final Collection<Contact> newSharers;
+
+	public SharingInvitationItem(Shareable shareable, boolean subscribed,
+			Collection<Contact> newSharers) {
+		super(shareable, subscribed);
+
+		this.newSharers = newSharers;
+	}
+
+	public Collection<Contact> getNewSharers() {
+		return newSharers;
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/sharing/SharingManager.java

@@ -0,0 +1,65 @@
+package org.briarproject.briar.api.sharing;
+
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.briar.api.client.SessionId;
+import org.briarproject.briar.api.messaging.ConversationManager.ConversationClient;
+
+import java.util.Collection;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+public interface SharingManager<S extends Shareable>
+		extends ConversationClient {
+
+	/**
+	 * Sends an invitation to share the given group with the given contact
+	 * and sends an optional message along with it.
+	 */
+	void sendInvitation(GroupId groupId, ContactId contactId,
+			@Nullable String message) throws DbException;
+
+	/**
+	 * Responds to a pending group invitation
+	 */
+	void respondToInvitation(S s, Contact c, boolean accept)
+			throws DbException;
+
+	/**
+	 * Responds to a pending group invitation
+	 */
+	void respondToInvitation(SessionId id, boolean accept)
+			throws DbException;
+
+	/**
+	 * Returns all group sharing messages sent by the Contact
+	 * identified by contactId.
+	 */
+	Collection<InvitationMessage> getInvitationMessages(
+			ContactId contactId) throws DbException;
+
+	/**
+	 * Returns all invitations to groups.
+	 */
+	Collection<SharingInvitationItem> getInvitations() throws DbException;
+
+	/**
+	 * Returns all contacts who are sharing the given group with us.
+	 */
+	Collection<Contact> getSharedBy(GroupId g) throws DbException;
+
+	/**
+	 * Returns all contacts with whom the given group is shared.
+	 */
+	Collection<Contact> getSharedWith(GroupId g) throws DbException;
+
+	/**
+	 * Returns true if the group not already shared and no invitation is open
+	 */
+	boolean canBeShared(GroupId g, Contact c) throws DbException;
+
+}

briar-api/src/main/java/org/briarproject/briar/api/sharing/SharingMessage.java

@@ -0,0 +1,144 @@
+package org.briarproject.briar.api.sharing;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfEntry;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.briar.api.client.SessionId;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+import static org.briarproject.briar.api.sharing.SharingConstants.GROUP_ID;
+import static org.briarproject.briar.api.sharing.SharingConstants.SESSION_ID;
+import static org.briarproject.briar.api.sharing.SharingConstants.SHARE_MSG_TYPE_ABORT;
+import static org.briarproject.briar.api.sharing.SharingConstants.SHARE_MSG_TYPE_ACCEPT;
+import static org.briarproject.briar.api.sharing.SharingConstants.SHARE_MSG_TYPE_DECLINE;
+import static org.briarproject.briar.api.sharing.SharingConstants.SHARE_MSG_TYPE_INVITATION;
+import static org.briarproject.briar.api.sharing.SharingConstants.SHARE_MSG_TYPE_LEAVE;
+import static org.briarproject.briar.api.sharing.SharingConstants.TIME;
+import static org.briarproject.briar.api.sharing.SharingConstants.TYPE;
+
+@NotNullByDefault
+public interface SharingMessage {
+
+	@Immutable
+	@NotNullByDefault
+	abstract class BaseMessage {
+
+		private final GroupId groupId;
+		private final SessionId sessionId;
+		private final long time;
+
+		BaseMessage(GroupId groupId, SessionId sessionId, long time) {
+			this.groupId = groupId;
+			this.sessionId = sessionId;
+			this.time = time;
+		}
+
+		public BdfList toBdfList() {
+			return BdfList.of(getType(), getSessionId());
+		}
+
+		public abstract BdfDictionary toBdfDictionary();
+
+		protected BdfDictionary toBdfDictionaryHelper() {
+			return BdfDictionary.of(
+					new BdfEntry(TYPE, getType()),
+					new BdfEntry(GROUP_ID, groupId),
+					new BdfEntry(SESSION_ID, sessionId)
+			);
+		}
+
+		public static BaseMessage from(InvitationFactory invitationFactory,
+				GroupId groupId, BdfDictionary d)
+				throws FormatException {
+
+			long type = d.getLong(TYPE);
+
+			if (type == SHARE_MSG_TYPE_INVITATION)
+				return invitationFactory.build(groupId, d);
+			else
+				return SimpleMessage.from(type, groupId, d);
+		}
+
+		public abstract long getType();
+
+		public GroupId getGroupId() {
+			return groupId;
+		}
+
+		public SessionId getSessionId() {
+			return sessionId;
+		}
+
+		public long getTime() {
+			return time;
+		}
+	}
+
+	@Immutable
+	@NotNullByDefault
+	abstract class Invitation extends BaseMessage {
+
+		@Nullable
+		protected final String message;
+
+		public Invitation(GroupId groupId, SessionId sessionId, long time,
+				@Nullable String message) {
+
+			super(groupId, sessionId, time);
+
+			this.message = message;
+		}
+
+		@Override
+		public long getType() {
+			return SHARE_MSG_TYPE_INVITATION;
+		}
+
+		@Nullable
+		public String getMessage() {
+			return message;
+		}
+	}
+
+	@Immutable
+	@NotNullByDefault
+	class SimpleMessage extends BaseMessage {
+
+		private final long type;
+
+		public SimpleMessage(long type, GroupId groupId, SessionId sessionId,
+				long time) {
+			super(groupId, sessionId, time);
+			this.type = type;
+		}
+
+		@Override
+		public long getType() {
+			return type;
+		}
+
+		@Override
+		public BdfDictionary toBdfDictionary() {
+			return toBdfDictionaryHelper();
+		}
+
+		public static SimpleMessage from(long type, GroupId groupId,
+				BdfDictionary d) throws FormatException {
+
+			if (type != SHARE_MSG_TYPE_ACCEPT &&
+					type != SHARE_MSG_TYPE_DECLINE &&
+					type != SHARE_MSG_TYPE_LEAVE &&
+					type != SHARE_MSG_TYPE_ABORT) throw new FormatException();
+
+			SessionId sessionId = new SessionId(d.getRaw(SESSION_ID));
+			long time = d.getLong(TIME);
+			return new SimpleMessage(type, groupId, sessionId, time);
+		}
+	}
+
+}

briar-api/src/main/java/org/briarproject/briar/api/sharing/event/InvitationRequestReceivedEvent.java

@@ -0,0 +1,38 @@
+package org.briarproject.briar.api.sharing.event;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.sharing.InvitationRequest;
+import org.briarproject.briar.api.sharing.Shareable;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public abstract class InvitationRequestReceivedEvent<S extends Shareable>
+		extends Event {
+
+	private final S shareable;
+	private final ContactId contactId;
+	private final InvitationRequest request;
+
+	protected InvitationRequestReceivedEvent(S shareable, ContactId contactId,
+			InvitationRequest request) {
+		this.shareable = shareable;
+		this.contactId = contactId;
+		this.request = request;
+	}
+
+	public ContactId getContactId() {
+		return contactId;
+	}
+
+	public InvitationRequest getRequest() {
+		return request;
+	}
+
+	public S getShareable() {
+		return shareable;
+	}
+}

briar-api/src/main/java/org/briarproject/briar/api/sharing/event/InvitationResponseReceivedEvent.java

@@ -0,0 +1,30 @@
+package org.briarproject.briar.api.sharing.event;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.api.sharing.InvitationResponse;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public abstract class InvitationResponseReceivedEvent extends Event {
+
+	private final ContactId contactId;
+	private final InvitationResponse response;
+
+	public InvitationResponseReceivedEvent(ContactId contactId,
+			InvitationResponse response) {
+		this.contactId = contactId;
+		this.response = response;
+	}
+
+	public ContactId getContactId() {
+		return contactId;
+	}
+
+	public InvitationResponse getResponse() {
+		return response;
+	}
+}