private String handleDataMessage(DataMessage data, List<TLV> tlvs) throws OtrException {
logger.finest(
getSessionID().getAccountID()
+ " received a data message from "
+ getSessionID().getUserID()
+ ".");
switch (this.getSessionStatus()) {
case ENCRYPTED:
logger.finest("Message state is ENCRYPTED. Trying to decrypt message.");
// Find matching session keys.
int senderKeyID = data.senderKeyID;
int receipientKeyID = data.recipientKeyID;
SessionKeys matchingKeys = this.getSessionKeysByID(receipientKeyID, senderKeyID);
if (matchingKeys == null) {
throw new OtrException("no matching keys found");
}
// Verify received MAC with a locally calculated MAC.
logger.finest("Transforming T to byte[] to calculate it's HmacSHA1.");
byte[] serializedT;
try {
serializedT = SerializationUtils.toByteArray(data.getT());
} catch (IOException e) {
throw new OtrException(e);
}
OtrCryptoEngine otrCryptoEngine = new OtrCryptoEngineImpl();
byte[] computedMAC =
otrCryptoEngine.sha1Hmac(
serializedT,
matchingKeys.getReceivingMACKey(),
SerializationConstants.TYPE_LEN_MAC);
if (!Arrays.equals(computedMAC, data.mac)) {
throw new OtrException("MAC verification failed, ignoring message");
}
logger.finest("Computed HmacSHA1 value matches sent one.");
// Mark this MAC key as old to be revealed.
matchingKeys.setIsUsedReceivingMACKey(true);
matchingKeys.setReceivingCtr(data.ctr);
byte[] dmc =
otrCryptoEngine.aesDecrypt(
matchingKeys.getReceivingAESKey(),
matchingKeys.getReceivingCtr(),
data.encryptedMessage);
String decryptedMsgContent;
try {
// Expect bytes to be text encoded in UTF-8.
decryptedMsgContent = new String(dmc, "UTF-8");
} catch (UnsupportedEncodingException e) {
throw new OtrException(e);
}
logger.finest("Decrypted message: \"" + decryptedMsgContent + "\"");
// FIXME extraKey = authContext.getExtraSymmetricKey();
// Rotate keys if necessary.
SessionKeys mostRecent = this.getMostRecentSessionKeys();
if (mostRecent.getLocalKeyID() == receipientKeyID) this.rotateLocalSessionKeys();
if (mostRecent.getRemoteKeyID() == senderKeyID) this.rotateRemoteSessionKeys(data.nextDH);
// Handle TLVs
if (tlvs == null) {
tlvs = new ArrayList<TLV>();
}
int tlvIndex = decryptedMsgContent.indexOf((char) 0x0);
if (tlvIndex > -1) {
decryptedMsgContent = decryptedMsgContent.substring(0, tlvIndex);
tlvIndex++;
byte[] tlvsb = new byte[dmc.length - tlvIndex];
System.arraycopy(dmc, tlvIndex, tlvsb, 0, tlvsb.length);
ByteArrayInputStream tin = new ByteArrayInputStream(tlvsb);
while (tin.available() > 0) {
int type;
byte[] tdata;
OtrInputStream eois = new OtrInputStream(tin);
try {
type = eois.readShort();
tdata = eois.readTlvData();
eois.close();
} catch (IOException e) {
throw new OtrException(e);
}
tlvs.add(new TLV(type, tdata));
}
}
if (tlvs.size() > 0) {
for (TLV tlv : tlvs) {
switch (tlv.getType()) {
case TLV.DISCONNECTED:
this.setSessionStatus(SessionStatus.FINISHED);
return null;
default:
for (OtrTlvHandler handler : tlvHandlers) {
handler.processTlv(tlv);
}
}
}
}
return decryptedMsgContent;
case FINISHED:
case PLAINTEXT:
showError("Unreadable encrypted message was received.");
injectMessage(
new ErrorMessage(
AbstractMessage.MESSAGE_ERROR, "You sent me an unreadable encrypted message"));
throw new OtrException("Unreadable encrypted message received");
}
return null;
}