diff --git a/bramble-api/src/main/java/org/briarproject/bramble/api/io/BlockSource.java b/bramble-api/src/main/java/org/briarproject/bramble/api/io/BlockSource.java
index 83a88a29f..926c5bbc6 100644
--- a/bramble-api/src/main/java/org/briarproject/bramble/api/io/BlockSource.java
+++ b/bramble-api/src/main/java/org/briarproject/bramble/api/io/BlockSource.java
@@ -1,11 +1,21 @@
 package org.briarproject.bramble.api.io;
 
 import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.NoSuchBlockException;
 import org.briarproject.bramble.api.sync.MessageId;
 
 public interface BlockSource {
 
+	/**
+	 * Returns the number of blocks in the given message.
+	 */
 	int getBlockCount(MessageId m) throws DbException;
 
+	/**
+	 * Returns the given block of the given message.
+	 *
+	 * @throws NoSuchBlockException if 'blockNumber' is greater than or equal
+	 * to the number of blocks in the message
+	 */
 	byte[] getBlock(MessageId m, int blockNumber) throws DbException;
 }
diff --git a/briar-api/src/main/java/org/briarproject/briar/api/client/ThreadedMessage.java b/briar-api/src/main/java/org/briarproject/briar/api/client/ThreadedMessage.java
index 37b0dc86f..d53223103 100644
--- a/briar-api/src/main/java/org/briarproject/briar/api/client/ThreadedMessage.java
+++ b/briar-api/src/main/java/org/briarproject/briar/api/client/ThreadedMessage.java
@@ -9,6 +9,8 @@ import org.briarproject.briar.api.messaging.PrivateMessage;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 
+import static java.util.Collections.emptyList;
+
 @Immutable
 @NotNullByDefault
 public abstract class ThreadedMessage extends PrivateMessage {
@@ -19,7 +21,7 @@ public abstract class ThreadedMessage extends PrivateMessage {
 
 	public ThreadedMessage(Message message, @Nullable MessageId parent,
 			Author author) {
-		super(message);
+		super(message, emptyList());
 		this.parent = parent;
 		this.author = author;
 	}
diff --git a/briar-api/src/main/java/org/briarproject/briar/api/messaging/PrivateMessage.java b/briar-api/src/main/java/org/briarproject/briar/api/messaging/PrivateMessage.java
index 2fe86deab..0c5a90b8d 100644
--- a/briar-api/src/main/java/org/briarproject/briar/api/messaging/PrivateMessage.java
+++ b/briar-api/src/main/java/org/briarproject/briar/api/messaging/PrivateMessage.java
@@ -3,6 +3,8 @@ package org.briarproject.briar.api.messaging;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.Message;
 
+import java.util.List;
+
 import javax.annotation.concurrent.Immutable;
 
 @Immutable
@@ -10,13 +12,18 @@ import javax.annotation.concurrent.Immutable;
 public class PrivateMessage {
 
 	private final Message message;
+	private final List<AttachmentHeader> attachments;
 
-	public PrivateMessage(Message message) {
+	public PrivateMessage(Message message, List<AttachmentHeader> attachments) {
 		this.message = message;
+		this.attachments = attachments;
 	}
 
 	public Message getMessage() {
 		return message;
 	}
 
+	public List<AttachmentHeader> getAttachmentHeaders() {
+		return attachments;
+	}
 }
diff --git a/briar-core/src/main/java/org/briarproject/briar/messaging/MessagingManagerImpl.java b/briar-core/src/main/java/org/briarproject/briar/messaging/MessagingManagerImpl.java
index bc92e6952..a0518a7a7 100644
--- a/briar-core/src/main/java/org/briarproject/briar/messaging/MessagingManagerImpl.java
+++ b/briar-core/src/main/java/org/briarproject/briar/messaging/MessagingManagerImpl.java
@@ -11,13 +11,16 @@ import org.briarproject.bramble.api.data.BdfList;
 import org.briarproject.bramble.api.data.MetadataParser;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 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.io.MessageInputStreamFactory;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.Client;
 import org.briarproject.bramble.api.sync.Group;
 import org.briarproject.bramble.api.sync.Group.Visibility;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.MessageStatus;
 import org.briarproject.bramble.api.versioning.ClientVersioningManager;
@@ -32,16 +35,17 @@ import org.briarproject.briar.api.messaging.PrivateMessageHeader;
 import org.briarproject.briar.api.messaging.event.PrivateMessageReceivedEvent;
 import org.briarproject.briar.client.ConversationClientImpl;
 
+import java.io.InputStream;
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Map;
-import java.util.Random;
 
 import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
 import static java.util.Collections.emptyList;
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_LENGTH;
 import static org.briarproject.briar.client.MessageTrackerConstants.MSG_KEY_READ;
 
 @Immutable
@@ -51,15 +55,21 @@ class MessagingManagerImpl extends ConversationClientImpl
 
 	private final ClientVersioningManager clientVersioningManager;
 	private final ContactGroupFactory contactGroupFactory;
+	private final MessageFactory messageFactory;
+	private final MessageInputStreamFactory messageInputStreamFactory;
 
 	@Inject
 	MessagingManagerImpl(DatabaseComponent db, ClientHelper clientHelper,
 			ClientVersioningManager clientVersioningManager,
 			MetadataParser metadataParser, MessageTracker messageTracker,
-			ContactGroupFactory contactGroupFactory) {
+			ContactGroupFactory contactGroupFactory,
+			MessageFactory messageFactory,
+			MessageInputStreamFactory messageInputStreamFactory) {
 		super(db, clientHelper, metadataParser, messageTracker);
 		this.clientVersioningManager = clientVersioningManager;
 		this.contactGroupFactory = contactGroupFactory;
+		this.messageFactory = messageFactory;
+		this.messageInputStreamFactory = messageInputStreamFactory;
 	}
 
 	@Override
@@ -142,9 +152,11 @@ class MessagingManagerImpl extends ConversationClientImpl
 			meta.put("read", true);
 			clientHelper.addLocalMessage(txn, m.getMessage(), meta, true);
 			messageTracker.trackOutgoingMessage(txn, m.getMessage());
+			for (AttachmentHeader h : m.getAttachmentHeaders())
+				db.setMessageShared(txn, h.getMessageId());
 			db.commitTransaction(txn);
 		} catch (FormatException e) {
-			throw new RuntimeException(e);
+			throw new AssertionError(e);
 		} finally {
 			db.endTransaction(txn);
 		}
@@ -152,11 +164,16 @@ class MessagingManagerImpl extends ConversationClientImpl
 
 	@Override
 	public AttachmentHeader addLocalAttachment(GroupId groupId, long timestamp,
-			String contentType, ByteBuffer data) {
-		// TODO add real implementation
-		byte[] b = new byte[MessageId.LENGTH];
-		new Random().nextBytes(b);
-		return new AttachmentHeader(new MessageId(b), "image/png");
+			String contentType, ByteBuffer data) throws DbException {
+		// TODO: Remove this restriction when large messages are supported
+		byte[] body = data.array();
+		if (body.length > MAX_MESSAGE_LENGTH) throw new DbException();
+		// TODO: Store message type and content type
+		Message m = messageFactory.createMessage(groupId, timestamp, body);
+		Metadata meta = new Metadata();
+		// Attachment will be shared when private message is added
+		db.transaction(false, txn -> db.addLocalMessage(txn, m, meta, false));
+		return new AttachmentHeader(m.getId(), contentType);
 	}
 
 	private ContactId getContactId(Transaction txn, GroupId g)
@@ -236,8 +253,9 @@ class MessagingManagerImpl extends ConversationClientImpl
 
 	@Override
 	public Attachment getAttachment(MessageId m) {
-		// TODO add real implementation
-		throw new IllegalStateException("Not yet implemented");
+		InputStream in = messageInputStreamFactory.getMessageInputStream(m);
+		// TODO: Read message type and content type
+		return new Attachment(in);
 	}
 
 }
diff --git a/briar-core/src/main/java/org/briarproject/briar/messaging/PrivateMessageFactoryImpl.java b/briar-core/src/main/java/org/briarproject/briar/messaging/PrivateMessageFactoryImpl.java
index d2c592787..bc250d57d 100644
--- a/briar-core/src/main/java/org/briarproject/briar/messaging/PrivateMessageFactoryImpl.java
+++ b/briar-core/src/main/java/org/briarproject/briar/messaging/PrivateMessageFactoryImpl.java
@@ -39,6 +39,6 @@ class PrivateMessageFactoryImpl implements PrivateMessageFactory {
 		// Serialise the message
 		BdfList message = BdfList.of(text);
 		Message m = clientHelper.createMessage(groupId, timestamp, message);
-		return new PrivateMessage(m);
+		return new PrivateMessage(m, attachments);
 	}
 }
diff --git a/briar-headless/src/test/java/org/briarproject/briar/headless/messaging/MessagingControllerImplTest.kt b/briar-headless/src/test/java/org/briarproject/briar/headless/messaging/MessagingControllerImplTest.kt
index c438a768b..fb6251548 100644
--- a/briar-headless/src/test/java/org/briarproject/briar/headless/messaging/MessagingControllerImplTest.kt
+++ b/briar-headless/src/test/java/org/briarproject/briar/headless/messaging/MessagingControllerImplTest.kt
@@ -62,7 +62,7 @@ internal class MessagingControllerImplTest : ControllerTest() {
             emptyList()
         )
     private val sessionId = SessionId(getRandomId())
-    private val privateMessage = PrivateMessage(message)
+    private val privateMessage = PrivateMessage(message, emptyList())
 
     @Test
     fun list() {