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[Curve25519] Use BouncyCastle instead of Chaos.NaCl #1447

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merged 3 commits into from
Jul 23, 2024
+26 −15
Merged

[Curve25519] Use BouncyCastle instead of Chaos.NaCl #1447

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beb3e9a
Curve25519 KEX is now based on BouncyCastle instead of Chaos.NaCl
scott-xu Jul 20, 2024
5bc19a3
Merge branch 'develop' into bc_x25519
WojciechNagorski Jul 23, 2024
cce2d40
Abstract SecureRandom
scott-xu Jul 23, 2024
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33 changes: 20 additions & 13 deletions src/Renci.SshNet/Security/KeyExchangeECCurve25519.cs
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Original file line number Diff line number Diff line change
@@ -1,14 +1,19 @@
using Renci.SshNet.Abstractions;
using System;

using Org.BouncyCastle.Crypto.Agreement;
using Org.BouncyCastle.Crypto.Generators;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Security;

using Renci.SshNet.Abstractions;
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 sealed class KeyExchangeECCurve25519 : KeyExchangeEC
{
private byte[] _privateKey;
private X25519Agreement _keyAgreement;

/// <summary>
/// Gets algorithm name.
Expand Down Expand Up @@ -38,13 +43,13 @@ public override void Start(Session session, KeyExchangeInitMessage message, bool

Session.KeyExchangeEcdhReplyMessageReceived += Session_KeyExchangeEcdhReplyMessageReceived;

var basepoint = new byte[MontgomeryCurve25519.PublicKeySizeInBytes];
basepoint[0] = 9;
var g = new X25519KeyPairGenerator();
g.Init(new X25519KeyGenerationParameters(new SecureRandom()));
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_privateKey = CryptoAbstraction.GenerateRandom(MontgomeryCurve25519.PrivateKeySizeInBytes);

_clientExchangeValue = new byte[MontgomeryCurve25519.PublicKeySizeInBytes];
MontgomeryOperations.scalarmult(_clientExchangeValue, 0, _privateKey, 0, basepoint, 0);
var aKeyPair = g.GenerateKeyPair();
_keyAgreement = new X25519Agreement();
_keyAgreement.Init(aKeyPair.Private);
_clientExchangeValue = ((X25519PublicKeyParameters)aKeyPair.Public).GetEncoded();

SendMessage(new KeyExchangeEcdhInitMessage(_clientExchangeValue));
}
Expand Down Expand Up @@ -96,9 +101,11 @@ private void HandleServerEcdhReply(byte[] hostKey, byte[] serverExchangeValue, b
_hostKey = hostKey;
_signature = signature;

var sharedKey = new byte[MontgomeryCurve25519.PublicKeySizeInBytes];
MontgomeryOperations.scalarmult(sharedKey, 0, _privateKey, 0, serverExchangeValue, 0);
SharedKey = sharedKey.ToBigInteger2().ToByteArray().Reverse();
var publicKey = new X25519PublicKeyParameters(serverExchangeValue);

var k1 = new byte[_keyAgreement.AgreementSize];
_keyAgreement.CalculateAgreement(publicKey, k1, 0);
SharedKey = k1.ToBigInteger2().ToByteArray().Reverse();
}
}
}