using Renci.SshNet.Common; using Renci.SshNet.Messages.Transport; using System; using System.Text; namespace Renci.SshNet.Security { internal abstract class KeyExchangeDiffieHellman : KeyExchange { protected BigInteger _group; protected BigInteger _prime; protected byte[] _clientPayload; protected byte[] _serverPayload; protected BigInteger _clientExchangeValue; protected BigInteger _serverExchangeValue; protected BigInteger _privateExponent; protected byte[] _hostKey; protected byte[] _signature; protected abstract int HashSize { get; } protected override bool ValidateExchangeHash() { byte[] data = CalculateHash(); uint count = Pack.BigEndianToUInt32(_hostKey); string string = Encoding.UTF8.GetString(_hostKey, 4, (int)count); KeyHostAlgorithm keyHostAlgorithm = base.Session.ConnectionInfo.HostKeyAlgorithms[string](_hostKey); base.Session.ConnectionInfo.CurrentHostKeyAlgorithm = string; if (CanTrustHostKey(keyHostAlgorithm)) return keyHostAlgorithm.VerifySignature(data, _signature); return false; } public override void Start(Session session, KeyExchangeInitMessage message) { base.Start(session, message); _serverPayload = message.GetBytes(); _clientPayload = base.Session.ClientInitMessage.GetBytes(); } protected void PopulateClientExchangeValue() { if (_group.IsZero) throw new ArgumentNullException("_group"); if (_prime.IsZero) throw new ArgumentNullException("_prime"); int bitLength = Math.Max(HashSize * 2, 1024); do { _privateExponent = BigInteger.Random(bitLength); _clientExchangeValue = BigInteger.ModPow(_group, _privateExponent, _prime); } while (_clientExchangeValue < 1 || _clientExchangeValue > _prime - (BigInteger)1); } protected virtual void HandleServerDhReply(byte[] hostKey, BigInteger serverExchangeValue, byte[] signature) { _serverExchangeValue = serverExchangeValue; _hostKey = hostKey; base.SharedKey = BigInteger.ModPow(serverExchangeValue, _privateExponent, _prime); _signature = signature; } } }