KEX with Elliptic Curve curve25519

Add Kex Algos curve25519-sha256(@libssh.org)

src/Renci.SshNet/ConnectionInfo.cs

@@ -322,6 +322,8 @@ namespace Renci.SshNet
 
             KeyExchangeAlgorithms = new Dictionary<string, Type>
                 {
+                    {"curve25519-sha256", typeof(KeyExchangeECCurve25519)},
+                    {"curve25519-sha256@libssh.org", typeof(KeyExchangeECCurve25519)},
                     {"ecdh-sha2-nistp256", typeof(KeyExchangeECDH256)},
                     {"ecdh-sha2-nistp384", typeof(KeyExchangeECDH384)},
                     {"ecdh-sha2-nistp521", typeof(KeyExchangeECDH521)},

src/Renci.SshNet/Renci.SshNet.csproj

@@ -310,6 +310,7 @@
     <Compile Include="Security\IKeyExchange.cs" />
     <Compile Include="Security\KeyExchangeDiffieHellmanGroupExchangeShaBase.cs" />
     <Compile Include="Security\KeyExchangeEC.cs" />
+    <Compile Include="Security\KeyExchangeECCurve25519.cs" />
     <Compile Include="Security\KeyExchangeECDH.cs" />
     <Compile Include="Security\KeyExchangeECDH521.cs" />
     <Compile Include="Security\KeyExchangeECDH384.cs" />

src/Renci.SshNet/Security/KeyExchangeECCurve25519.cs

@@ -0,0 +1,99 @@
+using System;
+using Renci.SshNet.Common;
+using Renci.SshNet.Messages.Transport;
+using Renci.SshNet.Security.Chaos.NaCl;
+using Renci.SshNet.Security.Chaos.NaCl.Internal.Ed25519Ref10;
+
+namespace Renci.SshNet.Security
+{
+    internal class KeyExchangeECCurve25519 : KeyExchangeEC
+    {
+        private byte[] _privateKey;
+
+        /// <summary>
+        /// Gets algorithm name.
+        /// </summary>
+        public override string Name
+        {
+            get { return "curve25519-sha256"; }
+        }
+
+        /// <summary>
+        /// Gets the size, in bits, of the computed hash code.
+        /// </summary>
+        /// <value>
+        /// The size, in bits, of the computed hash code.
+        /// </value>
+        protected override int HashSize
+        {
+            get { return 256; }
+        }
+
+        /// <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);
+
+            Session.RegisterMessage("SSH_MSG_KEX_ECDH_REPLY");
+
+            Session.KeyExchangeEcdhReplyMessageReceived += Session_KeyExchangeEcdhReplyMessageReceived;
+
+            var basepoint = new byte[MontgomeryCurve25519.PublicKeySizeInBytes];
+            basepoint[0] = 9;
+
+            var rnd = new Random();
+            _privateKey = new byte[MontgomeryCurve25519.PrivateKeySizeInBytes];
+            rnd.NextBytes(_privateKey);
+
+            _clientExchangeValue = new byte[MontgomeryCurve25519.PublicKeySizeInBytes];
+            MontgomeryOperations.scalarmult(_clientExchangeValue, 0, _privateKey, 0, basepoint, 0);
+
+            SendMessage(new KeyExchangeEcdhInitMessage(_clientExchangeValue));
+        }
+
+        /// <summary>
+        /// Finishes key exchange algorithm.
+        /// </summary>
+        public override void Finish()
+        {
+            base.Finish();
+
+            Session.KeyExchangeEcdhReplyMessageReceived -= Session_KeyExchangeEcdhReplyMessageReceived;
+        }
+
+        private void Session_KeyExchangeEcdhReplyMessageReceived(object sender, MessageEventArgs<KeyExchangeEcdhReplyMessage> e)
+        {
+            var message = e.Message;
+
+            //  Unregister message once received
+            Session.UnRegisterMessage("SSH_MSG_KEX_ECDH_REPLY");
+
+            HandleServerEcdhReply(message.KS, message.QS, message.Signature);
+
+            //  When SSH_MSG_KEXDH_REPLY received key exchange is completed
+            Finish();
+        }
+
+        /// <summary>
+        /// Handles the server DH reply message.
+        /// </summary>
+        /// <param name="hostKey">The host key.</param>
+        /// <param name="serverExchangeValue">The server exchange value.</param>
+        /// <param name="signature">The signature.</param>
+        protected override void HandleServerEcdhReply(byte[] hostKey, byte[] serverExchangeValue, byte[] signature)
+        {
+            _serverExchangeValue = serverExchangeValue;
+            _hostKey = hostKey;
+            _serverExchangeValue = serverExchangeValue;
+            _signature = signature;
+
+            var sharedKey = new byte[MontgomeryCurve25519.PublicKeySizeInBytes];
+            MontgomeryOperations.scalarmult(sharedKey, 0, _privateKey, 0, serverExchangeValue, 0);
+            SharedKey = sharedKey.ToBigInteger2();
+        }
+    }
+}