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Added optional padding to the frame format, so transports that are

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vulnerable to traffic analysis can frame their data independently of
packet boundaries.
This commit is contained in:
akwizgran
2011-08-19 14:47:16 +02:00
parent 7a53ea7814
commit 3084a6b058
6 changed files with 123 additions and 63 deletions
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22
components/net/sf/briar/transport/ConnectionReaderImpl.java
View File

@@ -31,8 +31,8 @@ implements ConnectionReader {
super(decrypter.getInputStream());
this.decrypter = decrypter;
this.mac = mac;
maxPayloadLength = MAX_FRAME_LENGTH - 6 - mac.getMacLength();
header = new byte[6];
maxPayloadLength = MAX_FRAME_LENGTH - 8 - mac.getMacLength();
header = new byte[8];
payload = new byte[maxPayloadLength];
footer = new byte[mac.getMacLength()];
}
@@ -83,9 +83,11 @@ implements ConnectionReader {
// Check that the frame has the expected frame number
if(ByteUtils.readUint32(header, 0) != frame)
throw new FormatException();
// Check that the payload length is legal
// Check that the payload and padding lengths are legal
payloadLen = ByteUtils.readUint16(header, 4);
if(payloadLen == 0 || payloadLen > maxPayloadLength)
int paddingLen = ByteUtils.readUint16(header, 6);
if(payloadLen + paddingLen == 0) throw new FormatException();
if(payloadLen + paddingLen > maxPayloadLength)
throw new FormatException();
frame++;
// Read the payload
@@ -97,6 +99,18 @@ implements ConnectionReader {
offset += read;
}
payloadOff = 0;
// Read the padding
while(offset < payloadLen + paddingLen) {
int read = in.read(payload, offset,
payloadLen + paddingLen - offset);
if(read == -1) throw new EOFException(); // Unexpected EOF
mac.update(payload, offset, read);
offset += read;
}
// Check that the padding is all zeroes
for(int i = payloadLen; i < payloadLen + paddingLen; i++) {
if(payload[i] != 0) throw new FormatException();
}
// Read the MAC
byte[] expectedMac = mac.doFinal();
decrypter.readMac(footer);

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

@@ -28,9 +28,9 @@ implements ConnectionWriter {
super(encrypter.getOutputStream());
this.encrypter = encrypter;
this.mac = mac;
maxPayloadLength = MAX_FRAME_LENGTH - 6 - mac.getMacLength();
maxPayloadLength = MAX_FRAME_LENGTH - 8 - mac.getMacLength();
buf = new ByteArrayOutputStream(maxPayloadLength);
header = new byte[6];
header = new byte[8];
}
public OutputStream getOutputStream() {