public static EcdhRatchetStep InitializeServer(IKeyDerivation kdf, IDigest digest,
IKeyAgreement previousKeyPair,
byte[] rootKey, ArraySegment <byte> remotePublicKey, IKeyAgreement keyPair,
byte[] receiveHeaderKey, byte[] sendHeaderKey)
{
if (receiveHeaderKey.Length != 32 || sendHeaderKey.Length != 32)
{
throw new InvalidOperationException("Keys need to be 32 bytes.");
}
Log.Verbose($"--Initialize ECDH Ratchet");
Log.Verbose($"Root Key: {Log.ShowBytes(rootKey)}");
Log.Verbose($"Prev ECDH Private: ({Log.ShowBytes(previousKeyPair.GetPublicKey())})");
Log.Verbose($"ECDH Public: {Log.ShowBytes(remotePublicKey)}");
Log.Verbose($"Curr ECDH Private: ({Log.ShowBytes(keyPair.GetPublicKey())})");
var e = new EcdhRatchetStep
{
EcdhKey = keyPair,
ReceiveHeaderKey = receiveHeaderKey,
SendHeaderKey = sendHeaderKey
};
// receive chain
Log.Verbose(" --Receiving Chain");
var rcderived = previousKeyPair.DeriveKey(remotePublicKey);
rcderived = digest.ComputeDigest(rcderived);
Log.Verbose($" C Input Key: {Log.ShowBytes(rootKey)}");
Log.Verbose($" C Key Info: {Log.ShowBytes(rcderived)}");
var rckeys = kdf.GenerateKeys(rcderived, rootKey, 3, 32);
Log.Verbose($" C Key Out 0: {Log.ShowBytes(rckeys[0])}");
Log.Verbose($" C Key Out 1: {Log.ShowBytes(rckeys[1])}");
Log.Verbose($" C Key Out 2: {Log.ShowBytes(rckeys[2])}");
rootKey = rckeys[0];
e.ReceivingChain.Initialize(rckeys[1]);
e.NextReceiveHeaderKey = rckeys[2];
// send chain
Log.Verbose(" --Sending Chain");
var scderived = keyPair.DeriveKey(remotePublicKey);
scderived = digest.ComputeDigest(scderived);
Log.Verbose($" C Input Key: {Log.ShowBytes(rootKey)}");
Log.Verbose($" C Key Info: {Log.ShowBytes(scderived)}");
var sckeys = kdf.GenerateKeys(scderived, rootKey, 3, 32);
Log.Verbose($" C Key Out 0: {Log.ShowBytes(sckeys[0])}");
Log.Verbose($" C Key Out 1: {Log.ShowBytes(sckeys[1])}");
Log.Verbose($" C Key Out 2: {Log.ShowBytes(sckeys[2])}");
rootKey = sckeys[0];
e.SendingChain.Initialize(sckeys[1]);
e.NextSendHeaderKey = sckeys[2];
// next root key
Log.Verbose($"Next Root Key: ({Log.ShowBytes(rootKey)})");
e.NextRootKey = rootKey;
return(e);
}
public static EcdhRatchetStep[] InitializeClient(IKeyDerivation kdf, IDigest digest,
byte[] rootKey, ArraySegment <byte> remotePublicKey0, ArraySegment <byte> remotePublicKey1, IKeyAgreement keyPair,
byte[] receiveHeaderKey, byte[] sendHeaderKey,
IKeyAgreement nextKeyPair)
{
if (receiveHeaderKey.Length != 32 || sendHeaderKey.Length != 32)
{
throw new InvalidOperationException("Keys need to be 32 bytes.");
}
Log.Verbose($"--Initialize ECDH Ratchet CLIENT");
Log.Verbose($"Root Key: {Log.ShowBytes(rootKey)}");
Log.Verbose($"ECDH Public 0: {Log.ShowBytes(remotePublicKey0)}");
Log.Verbose($"ECDH Public 1: {Log.ShowBytes(remotePublicKey1)}");
Log.Verbose($"ECDH Private: ({Log.ShowBytes(keyPair.GetPublicKey())})");
var e0 = new EcdhRatchetStep
{
EcdhKey = keyPair,
SendHeaderKey = sendHeaderKey
};
// receive chain doesn't exist
Log.Verbose(" --Receiving Chain");
// send chain
Log.Verbose(" --Sending Chain");
var scderived = keyPair.DeriveKey(remotePublicKey0);
scderived = digest.ComputeDigest(scderived);
Log.Verbose($" C Input Key: {Log.ShowBytes(rootKey)}");
Log.Verbose($" C Key Info: {Log.ShowBytes(scderived)}");
var sckeys = kdf.GenerateKeys(scderived, rootKey, 3, 32);
Log.Verbose($" C Key Out 0: {Log.ShowBytes(sckeys[0])}");
Log.Verbose($" C Key Out 1: {Log.ShowBytes(sckeys[1])}");
Log.Verbose($" C Key Out 2: {Log.ShowBytes(sckeys[2])}");
rootKey = sckeys[0];
e0.SendingChain.Initialize(sckeys[1]);
var nextSendHeaderKey = sckeys[2];
var e1 = InitializeServer(kdf, digest,
keyPair,
rootKey,
remotePublicKey1,
nextKeyPair,
receiveHeaderKey,
nextSendHeaderKey);
return(new[] { e0, e1 });
}
public static EcdhRatchetStep Create(IKeyAgreement EcdhKey, byte[] NextRootKey,
int receivingGeneration, byte[] receivingHeaderKey, byte[] receivingNextHeaderKey, byte[] receivingChainKey,
int sendingGeneration, byte[] sendingHeaderKey, byte[] sendingNextHeaderKey, byte[] sendingChainKey)
{
if (NextRootKey != null && NextRootKey.Length != 32)
{
throw new InvalidOperationException("The next root key size needs to be 32 bytes");
}
if (receivingHeaderKey != null && receivingHeaderKey.Length != 32)
{
throw new InvalidOperationException("The receiving header key size needs to be 32 bytes");
}
if (receivingNextHeaderKey != null && receivingNextHeaderKey.Length != 32)
{
throw new InvalidOperationException("The next receiving header key size needs to be 32 bytes");
}
if (receivingChainKey != null && receivingChainKey.Length != 32)
{
throw new InvalidOperationException("The receiving chain key size needs to be 32 bytes");
}
if (sendingHeaderKey != null && sendingHeaderKey.Length != 32)
{
throw new InvalidOperationException("The sending header key size needs to be 32 bytes");
}
if (sendingNextHeaderKey != null && sendingNextHeaderKey.Length != 32)
{
throw new InvalidOperationException("The next sending header key size needs to be 32 bytes");
}
if (sendingChainKey != null && sendingChainKey.Length != 32)
{
throw new InvalidOperationException("The sending chain key size needs to be 32 bytes");
}
var step = new EcdhRatchetStep()
{
EcdhKey = EcdhKey,
NextRootKey = NextRootKey,
ReceiveHeaderKey = receivingHeaderKey,
NextReceiveHeaderKey = receivingNextHeaderKey,
SendHeaderKey = sendingHeaderKey,
NextSendHeaderKey = sendingNextHeaderKey
};
step.ReceivingChain.Initialize(receivingChainKey);
step.ReceivingChain.Generation = receivingGeneration;
step.SendingChain.Initialize(sendingChainKey);
step.SendingChain.Generation = sendingGeneration;
return(step);
}
private void ReceiveFirstMessage(State state, byte[] payload, EcdhRatchetStep ecdhRatchetStep)
{
if (!(state is ServerState serverState))
{
throw new InvalidOperationException("Only the server can receive the first client message.");
}
if (serverState.FirstReceiveHeaderKey == null)
{
throw new InvalidOperationException("Invalid message received");
}
// check the first receive header key mac
var payloadExceptMac = new ArraySegment <byte>(payload, 0, payload.Length - MacSize);
var maciv = new ArraySegment <byte>(payload, 0, 16);
var mac = new ArraySegment <byte>(payload, payload.Length - MacSize, MacSize);
var Mac = new Poly(AesFactory);
Mac.Init(serverState.FirstReceiveHeaderKey, maciv, MacSize);
Mac.Process(payloadExceptMac);
var compareMac = Mac.Compute();
if (!mac.Matches(compareMac))
{
throw new InvalidOperationException("The first received message does not have the correct MAC");
}
var data = DeconstructMessage(state, payload, serverState.FirstReceiveHeaderKey, ecdhRatchetStep, false);
if (data.Length < InitializationNonceSize || !serverState.NextInitializationNonce.Matches(data, 0, InitializationNonceSize))
{
throw new InvalidOperationException("The first received message did not contain the correct payload");
}
serverState.FirstSendHeaderKey = null;
serverState.FirstReceiveHeaderKey = null;
serverState.LocalEcdhRatchetStep0 = null;
serverState.LocalEcdhRatchetStep1 = null;
serverState.RootKey = null;
}
private static void ShredRatchet(EcdhRatchetStep r)
{
(r.EcdhKey as IDisposable)?.Dispose();
r.EcdhKey = null;
r.NextReceiveHeaderKey?.Shred();
r.NextReceiveHeaderKey = null;
r.NextRootKey?.Shred();
r.NextRootKey = null;
r.NextSendHeaderKey?.Shred();
r.NextSendHeaderKey = null;
r.ReceiveHeaderKey?.Shred();
r.ReceiveHeaderKey = null;
r.SendHeaderKey?.Shred();
r.SendHeaderKey = null;
r.ReceivingChain.ChainKey?.Shred();
r.ReceivingChain.ChainKey = null;
r.ReceivingChain.OldChainKey?.Shred();
r.ReceivingChain.OldChainKey = null;
r.SendingChain.ChainKey?.Shred();
r.SendingChain.ChainKey = null;
r.SendingChain.OldChainKey?.Shred();
r.SendingChain.OldChainKey = null;
}
private byte[] ProcessInitialization(State state, byte[] dataReceived, byte[] headerKeyUsed, EcdhRatchetStep ecdhRatchetStep, bool usedApplicationHeaderKey)
{
byte[] sendback;
if (Configuration.IsClient)
{
Log.Verbose("\n\n###CLIENT");
var clientState = (ClientState)state;
if (dataReceived == null)
{
// step 1: send first init request from client
sendback = SendInitializationRequest(state);
}
else
{
if (usedApplicationHeaderKey)
{
if (clientState.Ratchets.Count == 0 && clientState.LocalEcdhForInit != null)
{
// step 2: init response from server
ReceiveInitializationResponse(clientState, dataReceived);
sendback = SendFirstClientMessage(clientState);
}
else
{
throw new InvalidOperationException("Unexpected initialization message");
}
}
else
{
// step 3: receive first message from server
ReceiveFirstResponse(clientState, dataReceived, headerKeyUsed, ecdhRatchetStep);
// initialization completed successfully.
sendback = null;
}
}
}
else
{
Log.Verbose("\n\n###SERVER");
var serverState = (ServerState)state;
if (dataReceived == null)
{
throw new InvalidOperationException("Only the client can send initialization without having received a response first");
}
if (usedApplicationHeaderKey)
{
// step 1: client init request
(ArraySegment <byte> initializationNonce, ArraySegment <byte> remoteEcdhForInit) = ReceiveInitializationRequest(serverState, dataReceived);
sendback = SendInitializationResponse(serverState, initializationNonce, remoteEcdhForInit);
}
else
{
// step 2: first message from client
ReceiveFirstMessage(serverState, dataReceived, ecdhRatchetStep);
sendback = SendFirstResponse(serverState);
}
}
if (sendback != null && sendback.Length > Configuration.MaximumMessageSize)
{
throw new InvalidOperationException("The MTU is too small");
}
return(sendback);
}
private byte[] DeconstructMessage(State state, byte[] payload, byte[] headerKey, EcdhRatchetStep ratchetUsed, bool usedNextHeaderKey)
{
if (state == null)
{
throw new ArgumentNullException(nameof(state));
}
if (payload == null)
{
throw new ArgumentNullException(nameof(payload));
}
if (headerKey == null)
{
throw new ArgumentNullException(nameof(headerKey));
}
var messageSize = payload.Length;
var encryptedNonce = new ArraySegment <byte>(payload, 0, NonceSize);
// decrypt the nonce
var headerEncryptionNonce = new ArraySegment <byte>(payload, payload.Length - MacSize - HeaderIVSize, HeaderIVSize);
var hcipher = new AesCtrMode(GetHeaderKeyCipher(headerKey), headerEncryptionNonce);
var decryptedNonce = hcipher.Process(encryptedNonce);
CheckNonce(headerEncryptionNonce);
// get the ecdh bit
var hasEcdh = (decryptedNonce[0] & 0b1000_0000) != 0;
decryptedNonce[0] &= 0b0111_1111;
// extract ecdh if needed
var step = BigEndianBitConverter.ToInt32(decryptedNonce);
if (hasEcdh)
{
var clientEcdhPublic = new ArraySegment <byte>(hcipher.Process(new ArraySegment <byte>(payload, NonceSize, EcNumSize)));
if (ratchetUsed == null)
{
// an override header key was used.
// this means we have to initialize the ratchet
if (!(state is ServerState serverState))
{
throw new InvalidOperationException("Only the server can initialize a ratchet.");
}
ratchetUsed = EcdhRatchetStep.InitializeServer(KeyDerivation, Digest,
serverState.LocalEcdhRatchetStep0,
serverState.RootKey, clientEcdhPublic,
serverState.LocalEcdhRatchetStep1,
serverState.FirstReceiveHeaderKey,
serverState.FirstSendHeaderKey);
serverState.Ratchets.Add(ratchetUsed);
}
else
{
if (usedNextHeaderKey)
{
// perform ecdh ratchet
IKeyAgreement newEcdh = KeyAgreementFactory.GenerateNew();
// this is the hottest line in the deconstruct process:
EcdhRatchetStep newRatchet = ratchetUsed.Ratchet(KeyDerivation, Digest, clientEcdhPublic, newEcdh);
state.Ratchets.Add(newRatchet);
ratchetUsed = newRatchet;
}
}
}
// get the inner payload key from the receive chain
if (ratchetUsed == null)
{
throw new InvalidOperationException("An override header key was used but the message did not contain ECDH parameters");
}
(var key, var _) = ratchetUsed.ReceivingChain.RatchetForReceiving(KeyDerivation, step);
CheckNonce(key);
// get the encrypted payload
var payloadOffset = hasEcdh ? NonceSize + EcNumSize : NonceSize;
var encryptedPayload = new ArraySegment <byte>(payload, payloadOffset, messageSize - payloadOffset - MacSize);
// decrypt the inner payload
var icipher = new AesCtrMode(AesFactory.GetAes(true, key), decryptedNonce);
var decryptedInnerPayload = icipher.Process(encryptedPayload);
return(decryptedInnerPayload);
}
private (byte[] headerKeyUsed, EcdhRatchetStep ratchetUsed, bool usedNextHeaderKey, bool usedApplicationKey) InterpretMessageMAC(State state, byte[] payload, byte[] overrideHeaderKey = null)
{
// get some basic parts
var messageSize = payload.Length;
var payloadExceptMac = new ArraySegment <byte>(payload, 0, messageSize - MacSize);
var mac = new ArraySegment <byte>(payload, messageSize - MacSize, MacSize);
// find the header key by checking the mac
var maciv = new byte[16];
Array.Copy(payload, maciv, 16);
var Mac = new Poly(AesFactory);
var usedNextHeaderKey = false;
var usedApplicationHeaderKey = false;
byte[] headerKey = null;
EcdhRatchetStep ratchetUsed = null;
if (overrideHeaderKey != null)
{
headerKey = overrideHeaderKey;
Mac.Init(headerKey, maciv, MacSize);
Mac.Process(payloadExceptMac);
var compareMac = Mac.Compute();
if (!mac.Matches(compareMac))
{
throw new InvalidOperationException("Could not decrypt the incoming message with given header key");
}
}
else
{
// if we are initialized check the mac using ratchet receive header keys.
if (state.Ratchets != null && !state.Ratchets.IsEmpty)
{
foreach (EcdhRatchetStep ratchet in state.Ratchets.Enumerate())
{
headerKey = ratchet.ReceiveHeaderKey;
Mac.Init(headerKey, maciv, MacSize);
Mac.Process(payloadExceptMac);
var compareMac = Mac.Compute();
if (mac.Matches(compareMac))
{
ratchetUsed = ratchet;
break;
}
else if (ratchet.NextReceiveHeaderKey != null)
{
headerKey = ratchet.NextReceiveHeaderKey;
Mac.Init(headerKey, maciv, MacSize);
Mac.Process(payloadExceptMac);
compareMac = Mac.Compute();
if (mac.Matches(compareMac))
{
usedNextHeaderKey = true;
ratchetUsed = ratchet;
break;
}
}
}
}
if (ratchetUsed == null)
{
// we're either not initialized or this is an initialization message.
// To determine that we mac using the application key
headerKey = Configuration.ApplicationKey;
Mac.Init(headerKey, maciv, MacSize);
Mac.Process(payloadExceptMac);
var compareMac = Mac.Compute();
if (mac.Matches(compareMac))
{
usedApplicationHeaderKey = true;
}
else
{
headerKey = null;
}
}
}
return(headerKey, ratchetUsed, usedNextHeaderKey, usedApplicationHeaderKey);
}
private byte[] ConstructMessage(ArraySegment <byte> message, bool includeEcdh, EcdhRatchetStep step)
{
if (message == null)
{
throw new ArgumentNullException(nameof(message));
}
// message format:
// <nonce (4)>, <payload, padding>, mac(12)
// <nonce (4), ecdh (32)>, <payload, padding>, mac(12)
// get the payload key and nonce
(var payloadKey, var messageNumber) = step.SendingChain.RatchetForSending(KeyDerivation);
var nonce = BigEndianBitConverter.GetBytes(messageNumber);
// make sure the first bit is not set as we use that bit to indicate
// the presence of new ECDH parameters
if ((nonce[0] & 0b1000_0000) != 0)
{
throw new InvalidOperationException($"The message number is too big. Cannot encrypt more than {((uint)1 << 31) - 1} messages without exchanging keys");
}
// calculate some sizes
var headerSize = NonceSize + (includeEcdh ? EcNumSize : 0);
var overhead = headerSize + MacSize;
var messageSize = message.Count;
var maxMessageSize = Configuration.MaximumMessageSize - overhead;
var minPayloadSize = Configuration.MinimumMessageSize - overhead;
// build the payload: <payload, padding>
ArraySegment <byte> payload;
if (messageSize < minPayloadSize)
{
payload = new ArraySegment <byte>(new byte[minPayloadSize]);
Array.Copy(message.Array, message.Offset, payload.Array, 0, message.Count);
}
else if (messageSize > maxMessageSize)
{
throw new InvalidOperationException("The message doesn't fit inside the MTU");
}
else
{
payload = message;
}
// encrypt the payload
var icipher = new AesCtrMode(AesFactory.GetAes(true, payloadKey), nonce);
var encryptedPayload = icipher.Process(payload);
// build the header: <nonce(4), ecdh(32)?>
var header = new byte[headerSize];
Array.Copy(nonce, header, NonceSize);
if (includeEcdh)
{
var ratchetPublicKey = step.GetPublicKey();
Array.Copy(ratchetPublicKey, 0, header, nonce.Length, ratchetPublicKey.Length);
// set the has ecdh bit
header[0] |= 0b1000_0000;
}
else
{
// clear the has ecdh bit
header[0] &= 0b0111_1111;
}
// encrypt the header using the header key and using the
// last 16 bytes of the message as the nonce.
var headerEncryptionNonce = new ArraySegment <byte>(encryptedPayload, encryptedPayload.Length - HeaderIVSize, HeaderIVSize);
var hcipher = new AesCtrMode(GetHeaderKeyCipher(step.SendHeaderKey), headerEncryptionNonce);
var encryptedHeader = hcipher.Process(header);
// mac the message: <header>, <payload>, mac(12)
// the mac uses the header encryption derived key (all 32 bytes)
var Mac = new Poly(AesFactory);
var maciv = new byte[16];
var epl = encryptedPayload.Length;
var ehl = encryptedHeader.Length;
if (ehl < maciv.Length)
{
Array.Copy(encryptedHeader, maciv, ehl);
Array.Copy(encryptedPayload, 0, maciv, ehl, 16 - ehl);
}
else
{
Array.Copy(encryptedHeader, maciv, maciv.Length);
}
Mac.Init(step.SendHeaderKey, maciv, MacSize);
Mac.Process(encryptedHeader);
Mac.Process(encryptedPayload);
var mac = Mac.Compute();
// construct the resulting message
var result = new byte[ehl + epl + mac.Length];
Array.Copy(encryptedHeader, 0, result, 0, ehl);
Array.Copy(encryptedPayload, 0, result, ehl, epl);
Array.Copy(mac, 0, result, ehl + epl, mac.Length);
return(result);
}
private void ReceiveFirstResponse(State state, byte[] data, byte[] headerKey, EcdhRatchetStep ecdhRatchetStep)
{
if (!(state is ClientState clientState))
{
throw new InvalidOperationException("Only the client can receive the first response.");
}
var contents = DeconstructMessage(state, data, headerKey, ecdhRatchetStep, false);
if (contents == null || contents.Length < InitializationNonceSize)
{
throw new InvalidOperationException("The first response from the server was not valid");
}
var nonce = new ArraySegment <byte>(contents, 0, InitializationNonceSize);
if (!nonce.Matches(clientState.InitializationNonce))
{
throw new InvalidOperationException("The first response from the server did not contain the correct nonce");
}
clientState.InitializationNonce = null;
}
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;
}
protected void ReadRatchet(Stream stream, IKeyAgreementFactory kexFac)
{
List <EcdhRatchetStep> steps = new List <EcdhRatchetStep>();
bool last = true;
bool secondToLast = false;
for (; ;)
{
// check if this is still a ratchet record
var b = stream.ReadByte();
stream.Seek(-1, SeekOrigin.Current);
if (b < 0 || (b & 0b1110_0000) == 0)
{
break;
}
if (last)
{
var genbytes = new byte[8];
stream.Read(genbytes, 0, 8);
genbytes[0] &= 0b0001_1111;
var rgeneration = BigEndianBitConverter.ToInt32(genbytes, 0); // hot
var sgeneration = BigEndianBitConverter.ToInt32(genbytes, 4); // hot and important
var ecdh = kexFac.Deserialize(stream);
var nextRootKey = new byte[KeySizeInBytes];
var sHeaderKey = new byte[KeySizeInBytes];
var sNextHeaderKey = new byte[KeySizeInBytes];
var sChainKey = new byte[KeySizeInBytes];
var rHeaderKey = new byte[KeySizeInBytes];
var rNextHeaderKey = new byte[KeySizeInBytes];
var rChainKey = new byte[KeySizeInBytes];
stream.Read(nextRootKey, 0, KeySizeInBytes); // cold
stream.Read(sHeaderKey, 0, KeySizeInBytes); // cold
stream.Read(sNextHeaderKey, 0, KeySizeInBytes); // cold
stream.Read(sChainKey, 0, KeySizeInBytes); // hot and important
stream.Read(rHeaderKey, 0, KeySizeInBytes); // cold
stream.Read(rNextHeaderKey, 0, KeySizeInBytes); // cold
stream.Read(rChainKey, 0, KeySizeInBytes); // hot
steps.Add(EcdhRatchetStep.Create(ecdh, nextRootKey, rgeneration, rHeaderKey, rNextHeaderKey, rChainKey,
sgeneration, sHeaderKey, sNextHeaderKey, sChainKey));
}
else if (secondToLast)
{
if ((b & 0b1000_0000) != 0)
{
// send and receive chain
var genbytes = new byte[8];
stream.Read(genbytes, 0, 8);
genbytes[0] &= 0b0001_1111;
var rgeneration = BigEndianBitConverter.ToInt32(genbytes, 0); // hot
var sgeneration = BigEndianBitConverter.ToInt32(genbytes, 4); // hot and important
var sHeaderKey = new byte[KeySizeInBytes];
var sChainKey = new byte[KeySizeInBytes];
var rHeaderKey = new byte[KeySizeInBytes];
var rChainKey = new byte[KeySizeInBytes];
stream.Read(sHeaderKey, 0, KeySizeInBytes); // cold
stream.Read(sChainKey, 0, KeySizeInBytes); // hot and important
stream.Read(rHeaderKey, 0, KeySizeInBytes); // cold
stream.Read(rChainKey, 0, KeySizeInBytes); // hot
steps.Add(EcdhRatchetStep.Create(null, null, rgeneration, rHeaderKey, null, rChainKey,
sgeneration, sHeaderKey, null, sChainKey));
}
else
{
// only sending chain - the client starts with only a sending chain as the first generation
var genbytes = new byte[4];
stream.Read(genbytes, 0, 4);
genbytes[0] &= 0b0001_1111;
var sgeneration = BigEndianBitConverter.ToInt32(genbytes, 0); // hot and important
var sHeaderKey = new byte[KeySizeInBytes];
var sChainKey = new byte[KeySizeInBytes];
stream.Read(sHeaderKey, 0, KeySizeInBytes); // cold
stream.Read(sChainKey, 0, KeySizeInBytes); // hot and important
steps.Add(EcdhRatchetStep.Create(null, null, 0, null, null, null,
sgeneration, sHeaderKey, null, sChainKey));
}
}