[PQC] Add support for sntrup761x25519-sha512 key exchange method

src/Renci.SshNet/ConnectionInfo.cs

@@ -349,6 +349,8 @@ public ConnectionInfo(string host, int port, string username, ProxyTypes proxyTy
 
             KeyExchangeAlgorithms = new Dictionary<string, Func<IKeyExchange>>
                 {
+                    { "sntrup761x25519-sha512", () => new KeyExchangeSNtruP761X25519Sha512() },
+                    { "[email protected]", () => new KeyExchangeSNtruP761X25519Sha512() },
                     { "curve25519-sha256", () => new KeyExchangeECCurve25519() },
                     { "[email protected]", () => new KeyExchangeECCurve25519() },
                     { "ecdh-sha2-nistp256", () => new KeyExchangeECDH256() },

src/Renci.SshNet/Security/KeyExchangeSNtruP761X25519Sha512.cs

@@ -0,0 +1,135 @@
+using System;
+using System.Globalization;
+using System.Linq;
+
+using Org.BouncyCastle.Crypto.Agreement;
+using Org.BouncyCastle.Crypto.Generators;
+using Org.BouncyCastle.Crypto.Parameters;
+using Org.BouncyCastle.Pqc.Crypto.NtruPrime;
+
+using Renci.SshNet.Abstractions;
+using Renci.SshNet.Common;
+using Renci.SshNet.Messages.Transport;
+
+namespace Renci.SshNet.Security
+{
+    internal sealed class KeyExchangeSNtruP761X25519Sha512 : KeyExchangeEC
+    {
+        private SNtruPrimeKemExtractor _sntrup761Extractor;
+        private X25519Agreement _x25519Agreement;
+
+        /// <summary>
+        /// Gets algorithm name.
+        /// </summary>
+        public override string Name
+        {
+            get { return "sntrup761x25519-sha512"; }
+        }
+
+        /// <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 512; }
+        }
+
+        /// <inheritdoc/>
+        public override void Start(Session session, KeyExchangeInitMessage message, bool sendClientInitMessage)
+        {
+            base.Start(session, message, sendClientInitMessage);
+
+            Session.RegisterMessage("SSH_MSG_KEX_ECDH_REPLY");
+
+            Session.KeyExchangeEcdhReplyMessageReceived += Session_KeyExchangeEcdhReplyMessageReceived;
+
+            var sntrup761KeyPairGenerator = new SNtruPrimeKeyPairGenerator();
+            sntrup761KeyPairGenerator.Init(new SNtruPrimeKeyGenerationParameters(CryptoAbstraction.SecureRandom, SNtruPrimeParameters.sntrup761));
+            var sntrup761KeyPair = sntrup761KeyPairGenerator.GenerateKeyPair();
+
+            _sntrup761Extractor = new SNtruPrimeKemExtractor((SNtruPrimePrivateKeyParameters)sntrup761KeyPair.Private);
+
+            var x25519KeyPairGenerator = new X25519KeyPairGenerator();
+            x25519KeyPairGenerator.Init(new X25519KeyGenerationParameters(CryptoAbstraction.SecureRandom));
+            var x25519KeyPair = x25519KeyPairGenerator.GenerateKeyPair();
+
+            _x25519Agreement = new X25519Agreement();
+            _x25519Agreement.Init(x25519KeyPair.Private);
+
+            var sntrup761PublicKey = ((SNtruPrimePublicKeyParameters)sntrup761KeyPair.Public).GetEncoded();
+            var x25519PublicKey = ((X25519PublicKeyParameters)x25519KeyPair.Public).GetEncoded();
+
+            _clientExchangeValue = sntrup761PublicKey.Concat(x25519PublicKey);
+
+            SendMessage(new KeyExchangeEcdhInitMessage(_clientExchangeValue));
+        }
+
+        /// <summary>
+        /// Finishes key exchange algorithm.
+        /// </summary>
+        public override void Finish()
+        {
+            base.Finish();
+
+            Session.KeyExchangeEcdhReplyMessageReceived -= Session_KeyExchangeEcdhReplyMessageReceived;
+        }
+
+        /// <summary>
+        /// Hashes the specified data bytes.
+        /// </summary>
+        /// <param name="hashData">The hash data.</param>
+        /// <returns>
+        /// The hash of the data.
+        /// </returns>
+        protected override byte[] Hash(byte[] hashData)
+        {
+            return CryptoAbstraction.HashSHA512(hashData);
+        }
+
+        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_KEX_ECDH_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>
+        private void HandleServerEcdhReply(byte[] hostKey, byte[] serverExchangeValue, byte[] signature)
+        {
+            _serverExchangeValue = serverExchangeValue;
+            _hostKey = hostKey;
+            _signature = signature;
+
+            if (serverExchangeValue.Length != _sntrup761Extractor.EncapsulationLength + X25519PublicKeyParameters.KeySize)
+            {
+                throw new SshConnectionException(
+                    string.Format(CultureInfo.CurrentCulture, "Bad Q_S length: {0}.", serverExchangeValue.Length),
+                    DisconnectReason.KeyExchangeFailed);
+            }
+
+            var sntrup761CipherText = serverExchangeValue.Take(_sntrup761Extractor.EncapsulationLength);
+            var secret = _sntrup761Extractor.ExtractSecret(sntrup761CipherText);
+            var sntrup761SecretLength = secret.Length;
+
+            var x25519PublicKey = new X25519PublicKeyParameters(serverExchangeValue, _sntrup761Extractor.EncapsulationLength);
+            Array.Resize(ref secret, sntrup761SecretLength + _x25519Agreement.AgreementSize);
+            _x25519Agreement.CalculateAgreement(x25519PublicKey, secret, sntrup761SecretLength);
+
+            SharedKey = CryptoAbstraction.HashSHA512(secret);
+        }
+    }
+}

test/Renci.SshNet.IntegrationTests/KeyExchangeAlgorithmTests.cs

@@ -22,6 +22,37 @@ public void TearDown()
             _remoteSshdConfig?.Reset();
         }
 
+        [TestMethod]
+        [Ignore]
+        public void SNtruP761X25519Sha512()
+        {
+            _remoteSshdConfig.ClearKeyExchangeAlgorithms()
+                             .AddKeyExchangeAlgorithm(KeyExchangeAlgorithm.SNtruP761X25519Sha512)
+                             .Update()
+                             .Restart();
+
+            using (var client = new SshClient(_connectionInfoFactory.Create()))
+            {
+                client.Connect();
+                client.Disconnect();
+            }
+        }
+
+        [TestMethod]
+        public void SNtruP761X25519Sha512OpenSsh()
+        {
+            _remoteSshdConfig.ClearKeyExchangeAlgorithms()
+                             .AddKeyExchangeAlgorithm(KeyExchangeAlgorithm.SNtruP761X25519Sha512OpenSsh)
+                             .Update()
+                             .Restart();
+
+            using (var client = new SshClient(_connectionInfoFactory.Create()))
+            {
+                client.Connect();
+                client.Disconnect();
+            }
+        }
+
         [TestMethod]
         public void Curve25519Sha256()
         {

test/Renci.SshNet.TestTools.OpenSSH/KeyExchangeAlgorithm.cs

@@ -14,7 +14,8 @@ public sealed class KeyExchangeAlgorithm
         public static readonly KeyExchangeAlgorithm EcdhSha2Nistp521 = new KeyExchangeAlgorithm("ecdh-sha2-nistp521");
         public static readonly KeyExchangeAlgorithm Curve25519Sha256 = new KeyExchangeAlgorithm("curve25519-sha256");
         public static readonly KeyExchangeAlgorithm Curve25519Sha256Libssh = new KeyExchangeAlgorithm("[email protected]");
-        public static readonly KeyExchangeAlgorithm Sntrup4591761x25519Sha512 = new KeyExchangeAlgorithm("[email protected]");
+        public static readonly KeyExchangeAlgorithm SNtruP761X25519Sha512 = new KeyExchangeAlgorithm("sntrup761x25519-sha512");
+        public static readonly KeyExchangeAlgorithm SNtruP761X25519Sha512OpenSsh = new KeyExchangeAlgorithm("[email protected]");
 
         public KeyExchangeAlgorithm(string name)
         {