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Add a plaintext receive buffer #1752

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2 changes: 1 addition & 1 deletion src/Renci.SshNet/Security/Cryptography/Ciphers/AesGcmCipher.BclImpl.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -39,7 +39,7 @@ public override void Decrypt(byte[] input, int cipherTextOffset, int cipherTextL

try
{
_aesGcm.Decrypt(_nonce, cipherText, tag, output.AsSpan(plainTextOffset), associatedData);
_aesGcm.Decrypt(_nonce, cipherText, tag, output.AsSpan(plainTextOffset, cipherTextLength), associatedData);
}
catch (AuthenticationTagMismatchException ex)
{
Expand Down
41 changes: 23 additions & 18 deletions src/Renci.SshNet/Session.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -200,6 +200,7 @@ public sealed class Session : ISession
private Socket _socket;

private ArrayBuffer _receiveBuffer = new(4 * 1024);
private byte[] _plaintextReceiveBuffer = new byte[4 * 1024];

/// <summary>
/// Gets the session semaphore that controls session channels.
Expand Down Expand Up @@ -1319,19 +1320,24 @@ private Message ReceiveMessage(Socket socket)

// Construct buffer for holding the payload and the inbound packet sequence as we need both in order
// to generate the hash.
var data = new byte[4 + totalPacketLength - serverMacLength];
var plaintextLength = 4 + totalPacketLength - serverMacLength;

BinaryPrimitives.WriteUInt32BigEndian(data, _inboundPacketSequence);
if (_plaintextReceiveBuffer.Length < plaintextLength)
{
Array.Resize(ref _plaintextReceiveBuffer, Math.Max(plaintextLength, 2 * _plaintextReceiveBuffer.Length));
}

BinaryPrimitives.WriteUInt32BigEndian(_plaintextReceiveBuffer, _inboundPacketSequence);

plainFirstBlock.AsSpan().CopyTo(data.AsSpan(4));
plainFirstBlock.AsSpan().CopyTo(_plaintextReceiveBuffer.AsSpan(4));

if (_serverMac != null && _serverEtm)
{
// ETM mac = MAC(key, sequence_number || packet_length || encrypted_packet)

// sequence_number
_ = _serverMac.TransformBlock(
inputBuffer: data,
inputBuffer: _plaintextReceiveBuffer,
inputOffset: 0,
inputCount: 4,
outputBuffer: null,
Expand Down Expand Up @@ -1363,21 +1369,23 @@ private Message ReceiveMessage(Socket socket)
input: _receiveBuffer.DangerousGetUnderlyingBuffer(),
offset: _receiveBuffer.ActiveStartOffset + blockSize,
length: numberOfBytesToDecrypt,
output: data,
output: _plaintextReceiveBuffer,
outputOffset: 4 + blockSize);

Debug.Assert(numberOfBytesDecrypted == numberOfBytesToDecrypt);
}
else
{
_receiveBuffer.ActiveReadOnlySpan.Slice(blockSize, numberOfBytesToDecrypt).CopyTo(data.AsSpan(4 + blockSize));
_receiveBuffer.ActiveReadOnlySpan
.Slice(blockSize, numberOfBytesToDecrypt)
.CopyTo(_plaintextReceiveBuffer.AsSpan(4 + blockSize));
}

if (_serverMac != null && !_serverEtm)
{
// non-ETM mac = MAC(key, sequence_number || unencrypted_packet)

var clientHash = _serverMac.ComputeHash(data);
var clientHash = _serverMac.ComputeHash(_plaintextReceiveBuffer, 0, plaintextLength);

if (!CryptoAbstraction.FixedTimeEquals(clientHash, _receiveBuffer.ActiveSpan.Slice(totalPacketLength - serverMacLength, serverMacLength)))
{
Expand All @@ -1387,19 +1395,16 @@ private Message ReceiveMessage(Socket socket)

_receiveBuffer.Discard(totalPacketLength);

var paddingLength = data[inboundPacketSequenceLength + packetLengthFieldLength];
var messagePayloadLength = packetLength - paddingLength - paddingLengthFieldLength;
var messagePayloadOffset = inboundPacketSequenceLength + packetLengthFieldLength + paddingLengthFieldLength;
var paddingLength = _plaintextReceiveBuffer[inboundPacketSequenceLength + packetLengthFieldLength];

ArraySegment<byte> payload = new(
_plaintextReceiveBuffer,
offset: inboundPacketSequenceLength + packetLengthFieldLength + paddingLengthFieldLength,
count: packetLength - paddingLength - paddingLengthFieldLength);

if (_serverDecompression != null)
{
data = _serverDecompression.Decompress(data, messagePayloadOffset, messagePayloadLength);

// Data now only contains the decompressed payload, and as such the offset is reset to zero
messagePayloadOffset = 0;

// The length of the payload is now the complete decompressed content
messagePayloadLength = data.Length;
payload = new(_serverDecompression.Decompress(payload.Array, payload.Offset, payload.Count));
}

_inboundPacketSequence++;
Expand All @@ -1411,7 +1416,7 @@ private Message ReceiveMessage(Socket socket)
throw new SshConnectionException("Inbound packet sequence number is about to wrap during initial key exchange.", DisconnectReason.KeyExchangeFailed);
}

return LoadMessage(data, messagePayloadOffset, messagePayloadLength);
return LoadMessage(payload.Array, payload.Offset, payload.Count);
}

private void TrySendDisconnect(DisconnectReason reasonCode, string message)
Expand Down