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Include the frame number in the header.

Browse Source 
This ensures the frame number is covered by the MAC, cleanly
separating encryption from authentication (previously we depended on
the encryption layer to garble frames if they were reordered).
This commit is contained in:
akwizgran
2011-12-02 13:37:44 +00:00
parent 14d5e6fe64
commit 51d58fadad
9 changed files with 144 additions and 80 deletions
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22
components/net/sf/briar/transport/ConnectionReaderImpl.java
View File

@@ -1,5 +1,6 @@
package net.sf.briar.transport;
import static net.sf.briar.api.transport.TransportConstants.FRAME_HEADER_LENGTH;
import static net.sf.briar.api.transport.TransportConstants.MAX_FRAME_LENGTH;
import static net.sf.briar.util.ByteUtils.MAX_32_BIT_UNSIGNED;
@@ -11,11 +12,10 @@ import java.security.InvalidKeyException;
import java.util.Arrays;
import javax.crypto.Mac;
import net.sf.briar.api.crypto.ErasableKey;
import net.sf.briar.api.FormatException;
import net.sf.briar.api.crypto.ErasableKey;
import net.sf.briar.api.transport.ConnectionReader;
import net.sf.briar.util.ByteUtils;
class ConnectionReaderImpl extends FilterInputStream
implements ConnectionReader {
@@ -41,8 +41,9 @@ implements ConnectionReader {
throw new IllegalArgumentException(e);
}
macKey.erase();
maxPayloadLength = MAX_FRAME_LENGTH - 4 - mac.getMacLength();
header = new byte[4];
maxPayloadLength =
MAX_FRAME_LENGTH - FRAME_HEADER_LENGTH - mac.getMacLength();
header = new byte[FRAME_HEADER_LENGTH];
payload = new byte[maxPayloadLength];
footer = new byte[mac.getMacLength()];
}
@@ -81,7 +82,6 @@ implements ConnectionReader {
assert betweenFrames;
// Don't allow more than 2^32 frames to be read
if(frame > MAX_32_BIT_UNSIGNED) throw new IllegalStateException();
frame++;
// Read the header
int offset = 0;
while(offset < header.length) {
@@ -91,13 +91,12 @@ implements ConnectionReader {
}
if(offset == 0) return false; // EOF between frames
if(offset < header.length) throw new EOFException(); // Unexpected EOF
mac.update(header);
// Check that the payload and padding lengths are legal
payloadLen = ByteUtils.readUint16(header, 0);
int paddingLen = ByteUtils.readUint16(header, 2);
if(payloadLen + paddingLen == 0) throw new FormatException();
if(payloadLen + paddingLen > maxPayloadLength)
// Check that the frame number is correct and the length is legal
if(!HeaderEncoder.validateHeader(header, frame, maxPayloadLength))
throw new FormatException();
payloadLen = HeaderEncoder.getPayloadLength(header);
int paddingLen = HeaderEncoder.getPaddingLength(header);
mac.update(header);
// Read the payload
offset = 0;
while(offset < payloadLen) {
@@ -124,6 +123,7 @@ implements ConnectionReader {
decrypter.readMac(footer);
if(!Arrays.equals(expectedMac, footer)) throw new FormatException();
betweenFrames = false;
frame++;
return true;
}
}

13
components/net/sf/briar/transport/ConnectionWriterImpl.java
View File

@@ -1,5 +1,6 @@
package net.sf.briar.transport;
import static net.sf.briar.api.transport.TransportConstants.FRAME_HEADER_LENGTH;
import static net.sf.briar.api.transport.TransportConstants.MAX_FRAME_LENGTH;
import static net.sf.briar.util.ByteUtils.MAX_32_BIT_UNSIGNED;
@@ -10,14 +11,15 @@ import java.io.OutputStream;
import java.security.InvalidKeyException;
import javax.crypto.Mac;
import net.sf.briar.api.crypto.ErasableKey;
import net.sf.briar.api.crypto.ErasableKey;
import net.sf.briar.api.transport.ConnectionWriter;
import net.sf.briar.util.ByteUtils;
/**
* A ConnectionWriter that buffers its input and writes a frame whenever there
* is a full-size frame to write or the flush() method is called.
* <p>
* This class is not thread-safe.
*/
class ConnectionWriterImpl extends FilterOutputStream
implements ConnectionWriter {
@@ -42,9 +44,10 @@ implements ConnectionWriter {
throw new IllegalArgumentException(badKey);
}
macKey.erase();
maxPayloadLength = MAX_FRAME_LENGTH - 4 - mac.getMacLength();
maxPayloadLength =
MAX_FRAME_LENGTH - FRAME_HEADER_LENGTH - mac.getMacLength();
buf = new ByteArrayOutputStream(maxPayloadLength);
header = new byte[4];
header = new byte[FRAME_HEADER_LENGTH];
}
public OutputStream getOutputStream() {
@@ -95,7 +98,7 @@ implements ConnectionWriter {
if(frame > MAX_32_BIT_UNSIGNED) throw new IllegalStateException();
byte[] payload = buf.toByteArray();
if(payload.length > maxPayloadLength) throw new IllegalStateException();
ByteUtils.writeUint16(payload.length, header, 0);
HeaderEncoder.encodeHeader(header, frame, payload.length, 0);
out.write(header);
mac.update(header);
out.write(payload);

45
components/net/sf/briar/transport/HeaderEncoder.java Normal file
View File

@@ -0,0 +1,45 @@
package net.sf.briar.transport;
import net.sf.briar.api.transport.TransportConstants;
import net.sf.briar.util.ByteUtils;
class HeaderEncoder {
static void encodeHeader(byte[] header, long frame, int payload,
int padding) {
if(header.length < TransportConstants.FRAME_HEADER_LENGTH)
throw new IllegalArgumentException();
if(frame < 0 || frame > ByteUtils.MAX_32_BIT_UNSIGNED)
throw new IllegalArgumentException();
if(payload < 0 || payload > ByteUtils.MAX_16_BIT_UNSIGNED)
throw new IllegalArgumentException();
if(padding < 0 || padding > ByteUtils.MAX_16_BIT_UNSIGNED)
throw new IllegalArgumentException();
ByteUtils.writeUint32(frame, header, 0);
ByteUtils.writeUint16(payload, header, 4);
ByteUtils.writeUint16(padding, header, 6);
}
static boolean validateHeader(byte[] header, long frame, int max) {
if(header.length < TransportConstants.FRAME_HEADER_LENGTH)
return false;
if(ByteUtils.readUint32(header, 0) != frame) return false;
int payload = ByteUtils.readUint16(header, 4);
int padding = ByteUtils.readUint16(header, 6);
if(payload + padding == 0) return false;
if(payload + padding > max) return false;
return true;
}
static int getPayloadLength(byte[] header) {
if(header.length < TransportConstants.FRAME_HEADER_LENGTH)
throw new IllegalArgumentException();
return ByteUtils.readUint16(header, 4);
}
static int getPaddingLength(byte[] header) {
if(header.length < TransportConstants.FRAME_HEADER_LENGTH)
throw new IllegalArgumentException();
return ByteUtils.readUint16(header, 6);
}
}

2
components/net/sf/briar/transport/IvEncoder.java
View File

@@ -5,7 +5,7 @@ import net.sf.briar.util.ByteUtils;
class IvEncoder {
static byte[] encodeIv(long frame, int blockSize) {
if(frame > ByteUtils.MAX_32_BIT_UNSIGNED)
if(frame < 0 || frame > ByteUtils.MAX_32_BIT_UNSIGNED)
throw new IllegalArgumentException();
byte[] iv = new byte[blockSize];
updateIv(iv, frame);

4
components/net/sf/briar/transport/TagEncoder.java
View File

@@ -12,7 +12,7 @@ import net.sf.briar.util.ByteUtils;
class TagEncoder {
static byte[] encodeTag(long frame, Cipher tagCipher, ErasableKey tagKey) {
if(frame > ByteUtils.MAX_32_BIT_UNSIGNED)
if(frame < 0 || frame > ByteUtils.MAX_32_BIT_UNSIGNED)
throw new IllegalArgumentException();
// The plaintext is blank
byte[] plaintext = new byte[TransportConstants.TAG_LENGTH];
@@ -32,6 +32,8 @@ class TagEncoder {
static boolean validateTag(byte[] tag, long frame, Cipher tagCipher,
ErasableKey tagKey) {
if(frame < 0 || frame > ByteUtils.MAX_32_BIT_UNSIGNED)
throw new IllegalArgumentException();
if(tag.length != TransportConstants.TAG_LENGTH) return false;
// Encode the frame number as a uint32 at the end of the IV
byte[] iv = new byte[tagCipher.getBlockSize()];