SSH.NET/Renci.SshClient/Renci.SshNet/Security/KeyExchangeDiffieHellmanGroupExchangeSha256.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Renci.SshNet.Messages.Transport;
using System.Security.Cryptography;
using Renci.SshNet.Messages;
using Renci.SshNet.Common;
using System.Diagnostics;
using Renci.SshNet.Security.Cryptography;

namespace Renci.SshNet.Security
{
    /// <summary>
    /// Represents "diffie-hellman-group-exchange-sha256" algorithm implementation.
    /// </summary>
    public class KeyExchangeDiffieHellmanGroupExchangeSha256 : KeyExchangeDiffieHellman
    {
        /// <summary>
        /// Gets algorithm name.
        /// </summary>
        public override string Name
        {
            get { return "diffie-hellman-group-exchange-sha256"; }
        }

        /// <summary>
        /// Starts key exchange algorithm
        /// </summary>
        /// <param name="session">The session.</param>
        /// <param name="message">Key exchange init message.</param>
        public override void Start(Session session, KeyExchangeInitMessage message)
        {
            base.Start(session, message);

            this.Session.RegisterMessage("SSH_MSG_KEX_DH_GEX_GROUP");
            this.Session.RegisterMessage("SSH_MSG_KEX_DH_GEX_REPLY");

            this.Session.MessageReceived += Session_MessageReceived;

            //  1. send SSH_MSG_KEY_DH_GEX_REQUEST
            this.SendMessage(new KeyExchangeDhGroupExchangeRequest(1024,1024,1024));
            
        }

        /// <summary>
        /// Finishes key exchange algorithm.
        /// </summary>
        public override void Finish()
        {
            base.Finish();

            this.Session.MessageReceived -= Session_MessageReceived;
        }

        /// <summary>
        /// Calculates key exchange hash value.
        /// </summary>
        /// <returns>
        /// Key exchange hash.
        /// </returns>
        protected override byte[] CalculateHash()
        {
            var hashData = new _ExchangeHashData
            {
                ClientVersion = this.Session.ClientVersion,
                ServerVersion = this.Session.ServerVersion,
                ClientPayload = this._clientPayload,
                ServerPayload = this._serverPayload,
                HostKey = this._hostKey,
                MinimumGroupSize = 1024,
                PreferredGroupSize = 1024,
                MaximumGroupSize = 1024,
                Prime = this._prime,
                SubGroup = this._group,
                ClientExchangeValue = this._clientExchangeValue,
                ServerExchangeValue = this._serverExchangeValue,
                SharedKey = this.SharedKey,
            }.GetBytes();

            return this.Hash(hashData);
        }

        /// <summary>
        /// Hashes the specified data bytes.
        /// </summary>
        /// <param name="hashBytes">Data to hash.</param>
        /// <returns>
        /// Hashed bytes
        /// </returns>
        protected override byte[] Hash(byte[] hashBytes)
        {
            using (var md = new SHA256Hash())
            {
                return md.ComputeHash(hashBytes);
            }
        }

        private void Session_MessageReceived(object sender, MessageEventArgs<Message> e)
        {
            var groupMessage = e.Message as KeyExchangeDhGroupExchangeGroup;

            if (groupMessage != null)
            {
                //  Unregister message once received
                this.Session.UnRegisterMessage("SSH_MSG_KEX_DH_GEX_GROUP");

                //  2. Receive SSH_MSG_KEX_DH_GEX_GROUP
                this._prime = groupMessage.SafePrime;
                this._group = groupMessage.SubGroup;

                this.PopulateClientExchangeValue();

                //  3. Send SSH_MSG_KEX_DH_GEX_INIT
                this.SendMessage(new KeyExchangeDhGroupExchangeInit(this._clientExchangeValue));
            }
            var replyMessage = e.Message as KeyExchangeDhGroupExchangeReply;

            if (replyMessage != null)
            {
                //  Unregister message once received
                this.Session.UnRegisterMessage("SSH_MSG_KEX_DH_GEX_REPLY");

                this.HandleServerDhReply(replyMessage.HostKey, replyMessage.F, replyMessage.Signature);

                //  When SSH_MSG_KEX_DH_GEX_REPLY received key exchange is completed
                this.Finish();
            }
        }

        private class _ExchangeHashData : SshData
        {
            public string ServerVersion { get; set; }

            public string ClientVersion { get; set; }

            public byte[] ClientPayload { get; set; }

            public byte[] ServerPayload { get; set; }

            public byte[] HostKey { get; set; }

            public UInt32 MinimumGroupSize { get; set; }

            public UInt32 PreferredGroupSize { get; set; }

            public UInt32 MaximumGroupSize { get; set; }

            public BigInteger Prime { get; set; }

            public BigInteger SubGroup { get; set; }

            public BigInteger ClientExchangeValue { get; set; }

            public BigInteger ServerExchangeValue { get; set; }

            public BigInteger SharedKey { get; set; }

            protected override void LoadData()
            {
                throw new System.NotImplementedException();
            }

            protected override void SaveData()
            {
                this.Write(this.ClientVersion);
                this.Write(this.ServerVersion);
                this.WriteBinaryString(this.ClientPayload);
                this.WriteBinaryString(this.ServerPayload);
                this.WriteBinaryString(this.HostKey);
                this.Write(this.MinimumGroupSize);
                this.Write(this.PreferredGroupSize);
                this.Write(this.MaximumGroupSize);
                this.Write(this.Prime);
                this.Write(this.SubGroup);
                this.Write(this.ClientExchangeValue);
                this.Write(this.ServerExchangeValue);
                this.Write(this.SharedKey);
            }
        }
    }
}