public void BasicTest()
{
byte[] bytes1 = new byte[100];
byte[] bytes2 = new byte[100];
bytes1[0] = 1;
bytes2[0] = 2;
Digest d = new Digest();
var d1 = d.ComputeDigest(bytes1);
var d2 = d.ComputeDigest(bytes2);
Assert.NotEqual(d1, d2);
}
private byte[] SendInitializationRequest(State state)
{
// message format:
// nonce(16), pubkey(32), ecdh(32), padding(...), signature(64), mac(12)
if (!(state is ClientState clientState))
{
throw new InvalidOperationException("Only the client can send init request.");
}
// 16 bytes nonce
clientState.InitializationNonce = RandomNumberGenerator.Generate(InitializationNonceSize);
// get the public key
var pubkey = Signature.GetPublicKey();
// generate new ECDH keypair for init message and root key
IKeyAgreement clientEcdh = KeyAgreementFactory.GenerateNew();
clientState.LocalEcdhForInit = clientEcdh;
// nonce(16), <pubkey(32), ecdh(32), signature(64)>, mac(12)
var initializationMessageSize = InitializationNonceSize + EcNumSize * 4 + MacSize;
var messageSize = Math.Max(Configuration.MinimumMessageSize, initializationMessageSize);
var initializationMessageSizeWithSignature = messageSize - MacSize;
var initializationMessageSizeWithoutSignature = messageSize - MacSize - SignatureSize;
var signatureOffset = messageSize - MacSize - SignatureSize;
var message = new byte[messageSize];
Array.Copy(clientState.InitializationNonce, 0, message, 0, InitializationNonceSize);
Array.Copy(pubkey, 0, message, InitializationNonceSize, EcNumSize);
Array.Copy(clientEcdh.GetPublicKey(), 0, message, InitializationNonceSize + EcNumSize, EcNumSize);
// sign the message
var digest = Digest.ComputeDigest(message, 0, initializationMessageSizeWithoutSignature);
Array.Copy(Signature.Sign(digest), 0, message, signatureOffset, SignatureSize);
// encrypt the message with the application key
var cipher = new AesCtrMode(AesFactory.GetAes(true, Configuration.ApplicationKey), clientState.InitializationNonce);
var encryptedPayload = cipher.Process(message, InitializationNonceSize, initializationMessageSizeWithSignature - InitializationNonceSize);
Array.Copy(encryptedPayload, 0, message, InitializationNonceSize, initializationMessageSizeWithSignature - InitializationNonceSize);
// calculate mac
var Mac = new Poly(AesFactory);
Mac.Init(Configuration.ApplicationKey, clientState.InitializationNonce, MacSize);
Mac.Process(message, 0, initializationMessageSizeWithSignature);
var mac = Mac.Compute();
Array.Copy(mac, 0, message, initializationMessageSizeWithSignature, MacSize);
return(message);
}
private void ReceiveInitializationResponse(State state, byte[] data)
{
if (!(state is ClientState clientState))
{
throw new InvalidOperationException("Only the client can receive an init response.");
}
var messageSize = data.Length;
var macOffset = messageSize - MacSize;
var headerIvOffset = macOffset - HeaderIVSize;
var headerSize = InitializationNonceSize + EcNumSize;
var payloadSize = messageSize - headerSize - MacSize;
// decrypt header
var cipher = new AesCtrMode(AesFactory.GetAes(true, Configuration.ApplicationKey), data, headerIvOffset, HeaderIVSize);
var decryptedHeader = cipher.Process(data, 0, headerSize);
Array.Copy(decryptedHeader, 0, data, 0, headerSize);
// new nonce(16), ecdh pubkey(32), <nonce(16), server pubkey(32),
// new ecdh pubkey(32) x2, signature(64)>, mac(12)
var nonce = new ArraySegment <byte>(data, 0, InitializationNonceSize);
var rootEcdhKey = new ArraySegment <byte>(data, InitializationNonceSize, EcNumSize);
var encryptedPayload = new ArraySegment <byte>(data, headerSize, payloadSize);
CheckNonce(nonce);
// decrypt payload
IKeyAgreement rootEcdh = clientState.LocalEcdhForInit;
var rootPreKey = rootEcdh.DeriveKey(rootEcdhKey);
rootPreKey = Digest.ComputeDigest(rootPreKey);
cipher = new AesCtrMode(AesFactory.GetAes(true, rootPreKey), nonce);
var decryptedPayload = cipher.Process(encryptedPayload);
Array.Copy(decryptedPayload, 0, data, headerSize, payloadSize);
// extract some goodies
var oldNonce = new ArraySegment <byte>(data, headerSize, InitializationNonceSize);
var serverPubKey = new ArraySegment <byte>(data, headerSize + InitializationNonceSize, EcNumSize);
var remoteRatchetEcdh0 = new ArraySegment <byte>(data, headerSize + InitializationNonceSize + EcNumSize, EcNumSize);
var remoteRatchetEcdh1 = new ArraySegment <byte>(data, headerSize + InitializationNonceSize + EcNumSize * 2, EcNumSize);
// make sure the nonce sent back by the server (which is encrypted and signed)
// matches the nonce we sent previously
if (!oldNonce.Matches(clientState.InitializationNonce))
{
throw new InvalidOperationException("Nonce did not match");
}
// verify that the signature matches
IVerifier verifier = VerifierFactory.Create(serverPubKey);
if (!verifier.VerifySignedMessage(Digest, new ArraySegment <byte>(data, 0, payloadSize + headerSize)))
{
throw new InvalidOperationException("The signature was invalid");
}
// keep the server public key around
clientState.ServerPublicKey = serverPubKey.ToArray();
// store the new nonce we got from the server
clientState.InitializationNonce = nonce.ToArray();
Log.Verbose($"storing iniitlizaionta nonce: {Log.ShowBytes(nonce)}");
// we now have enough information to construct our double ratchet
IKeyAgreement localStep0EcdhRatchet = KeyAgreementFactory.GenerateNew();
IKeyAgreement localStep1EcdhRatchet = KeyAgreementFactory.GenerateNew();
// initialize client root key and ecdh ratchet
var genKeys = KeyDerivation.GenerateKeys(rootPreKey, clientState.InitializationNonce, 3, 32);
var rootKey = genKeys[0];
var receiveHeaderKey = genKeys[1];
var sendHeaderKey = genKeys[2];
clientState.Ratchets.Add(EcdhRatchetStep.InitializeClient(KeyDerivation, Digest, rootKey,
remoteRatchetEcdh0, remoteRatchetEcdh1, localStep0EcdhRatchet,
receiveHeaderKey, sendHeaderKey,
localStep1EcdhRatchet));
clientState.LocalEcdhForInit = null;
}
private byte[] SendInitializationResponse(State state, ArraySegment <byte> initializationNonce, ArraySegment <byte> remoteEcdhForInit)
{
// message format:
// new nonce(16), ecdh pubkey(32),
// <nonce from init request(16), server pubkey(32),
// new ecdh pubkey(32) x2, Padding(...), signature(64)>, mac(12) = 236 bytes
if (!(state is ServerState serverState))
{
throw new InvalidOperationException("Only the server can send init response.");
}
// generate a nonce and new ecdh parms
var serverNonce = RandomNumberGenerator.Generate(InitializationNonceSize);
serverState.NextInitializationNonce = serverNonce;
IKeyAgreement rootPreEcdh = KeyAgreementFactory.GenerateNew();
var rootPreEcdhPubkey = rootPreEcdh.GetPublicKey();
// generate server ECDH for root key and root key
var rootPreKey = rootPreEcdh.DeriveKey(remoteEcdhForInit);
rootPreKey = Digest.ComputeDigest(rootPreKey);
var genKeys = KeyDerivation.GenerateKeys(rootPreKey, serverNonce, 3, EcNumSize);
serverState.RootKey = genKeys[0];
serverState.FirstSendHeaderKey = genKeys[1];
serverState.FirstReceiveHeaderKey = genKeys[2];
// generate two server ECDH. One for ratchet 0 sending key and one for the next
// this is enough for the server to generate a receiving chain key and sending
// chain key as soon as the client sends a sending chain key
IKeyAgreement serverEcdhRatchet0 = KeyAgreementFactory.GenerateNew();
serverState.LocalEcdhRatchetStep0 = serverEcdhRatchet0;
IKeyAgreement serverEcdhRatchet1 = KeyAgreementFactory.GenerateNew();
serverState.LocalEcdhRatchetStep1 = serverEcdhRatchet1;
var minimumMessageSize = InitializationNonceSize * 2 + EcNumSize * 6 + MacSize;
var entireMessageSize = Math.Max(Configuration.MinimumMessageSize, minimumMessageSize);
var macOffset = entireMessageSize - MacSize;
var entireMessageWithoutMacOrSignatureSize = macOffset - SignatureSize;
var encryptedPayloadOffset = InitializationNonceSize + EcNumSize;
var encryptedPayloadSize = macOffset - encryptedPayloadOffset;
// construct the message
var message = new byte[entireMessageSize];
Array.Copy(serverNonce, 0, message, 0, InitializationNonceSize);
Array.Copy(rootPreEcdhPubkey, 0, message, InitializationNonceSize, EcNumSize);
// construct the to-be-encrypted part
var rre0 = serverEcdhRatchet0.GetPublicKey();
var rre1 = serverEcdhRatchet1.GetPublicKey();
Array.Copy(initializationNonce.Array, initializationNonce.Offset, message, encryptedPayloadOffset, InitializationNonceSize);
Array.Copy(Signature.GetPublicKey(), 0, message, encryptedPayloadOffset + InitializationNonceSize, EcNumSize);
Array.Copy(rre0, 0, message, encryptedPayloadOffset + InitializationNonceSize + EcNumSize, EcNumSize);
Array.Copy(rre1, 0, message, encryptedPayloadOffset + InitializationNonceSize + EcNumSize * 2, EcNumSize);
// sign the message
var digest = Digest.ComputeDigest(message, 0, entireMessageWithoutMacOrSignatureSize);
Array.Copy(Signature.Sign(digest), 0, message, entireMessageWithoutMacOrSignatureSize, SignatureSize);
// encrypt the message
var cipher = new AesCtrMode(AesFactory.GetAes(true, rootPreKey), serverNonce);
var encryptedPayload = cipher.Process(message, encryptedPayloadOffset, encryptedPayloadSize);
Array.Copy(encryptedPayload, 0, message, encryptedPayloadOffset, encryptedPayloadSize);
// encrypt the header
cipher = new AesCtrMode(AesFactory.GetAes(true, Configuration.ApplicationKey), encryptedPayload, encryptedPayloadSize - HeaderIVSize, HeaderIVSize);
var encryptedHeader = cipher.Process(message, 0, encryptedPayloadOffset);
Array.Copy(encryptedHeader, 0, message, 0, encryptedPayloadOffset);
// calculate mac
var Mac = new Poly(AesFactory);
Mac.Init(Configuration.ApplicationKey, encryptedHeader, 0, InitializationNonceSize, MacSize);
Mac.Process(message, 0, macOffset);
var mac = Mac.Compute();
Array.Copy(mac, 0, message, macOffset, MacSize);
return(message);
}
