//writer util
private SSH2DataWriter OpenWriter(AgentForwadPacketType pt) {
SSH2DataWriter wr = new SSH2DataWriter();
wr.WriteInt32(0); //length field
wr.WriteByte((byte)pt);
return wr;
}
private byte[] DeriveKey(BigInteger key, byte[] hash, char ch, int length) {
byte[] result = new byte[length];
SSH2DataWriter wr = new SSH2DataWriter();
wr.WriteBigInteger(key);
wr.Write(hash);
wr.WriteByte((byte)ch);
wr.Write(_sessionID);
byte[] h1 = new SHA1CryptoServiceProvider().ComputeHash(wr.ToByteArray());
if (h1.Length >= length) {
Array.Copy(h1, 0, result, 0, length);
return result;
}
else {
wr = new SSH2DataWriter();
wr.WriteBigInteger(key);
wr.Write(_sessionID);
wr.Write(h1);
byte[] h2 = new SHA1CryptoServiceProvider().ComputeHash(wr.ToByteArray());
if (h1.Length + h2.Length >= length) {
Array.Copy(h1, 0, result, 0, h1.Length);
Array.Copy(h2, 0, result, h1.Length, length - h1.Length);
return result;
}
else
throw new SSHException("necessary key length is too big"); //long key is not supported
}
}
