private byte[] ComputeEncryptionKey(IKexAlgorithm kexAlgorithm, byte[] exchangeHash, uint keySize, byte[] sharedSecret, char letter)
{
// K(X) = HASH(K || H || X || session_id)
// Prepare the buffer
byte[] keyBuffer = new byte[keySize];
int keyBufferIndex = 0;
int currentHashLength = 0;
byte[] currentHash = null;
// We can stop once we fill the key buffer
while (keyBufferIndex < keySize)
{
using (ByteWriter writer = new ByteWriter())
{
// Write "K"
writer.WriteMPInt(sharedSecret);
// Write "H"
writer.WriteRawBytes(exchangeHash);
if (currentHash == null)
{
// If we haven't done this yet, add the "X" and session_id
writer.WriteByte((byte)letter);
writer.WriteRawBytes(m_SessionId);
}
else
{
// If the key isn't long enough after the first pass, we need to
// write the current hash as described here:
// K1 = HASH(K || H || X || session_id) (X is e.g., "A")
// K2 = HASH(K || H || K1)
// K3 = HASH(K || H || K1 || K2)
// ...
// key = K1 || K2 || K3 || ...
writer.WriteRawBytes(currentHash);
}
currentHash = kexAlgorithm.ComputeHash(writer.ToByteArray());
}
currentHashLength = Math.Min(currentHash.Length, (int)(keySize - keyBufferIndex));
Array.Copy(currentHash, 0, keyBuffer, keyBufferIndex, currentHashLength);
keyBufferIndex += currentHashLength;
}
return(keyBuffer);
}
public IKexAlgorithm PickKexAlgorithm()
{
foreach (string algo in this.KexAlgorithms)
{
IKexAlgorithm selectedAlgo = Server.GetType <IKexAlgorithm>(Server.SupportedKexAlgorithms, algo);
if (selectedAlgo != null)
{
return(selectedAlgo);
}
}
// If no algorithm satisfying all these conditions can be found, the
// connection fails, and both sides MUST disconnect.
throw new SSHServerException(DisconnectReason.SSH_DISCONNECT_KEY_EXCHANGE_FAILED, "Could not find a shared Kex Algorithm");
}
private byte[] ComputeExchangeHash(IKexAlgorithm kexAlgorithm, byte[] hostKeyAndCerts, byte[] clientExchangeValue, byte[] serverExchangeValue, byte[] sharedSecret)
{
// H = hash(V_C || V_S || I_C || I_S || K_S || e || f || K)
using (ByteWriter writer = new ByteWriter())
{
writer.WriteString(m_ProtocolVersionExchange);
writer.WriteString(Server.ProtocolVersionExchange);
writer.WriteBytes(m_KexInitClientToServer.GetBytes());
writer.WriteBytes(m_KexInitServerToClient.GetBytes());
writer.WriteBytes(hostKeyAndCerts);
writer.WriteMPInt(clientExchangeValue);
writer.WriteMPInt(serverExchangeValue);
writer.WriteMPInt(sharedSecret);
return(kexAlgorithm.ComputeHash(writer.ToByteArray()));
}
}
