public byte[] PackSrtpPacket(RtpPacket packet)
{
var offset = 0;
var buffer = new byte[RtpPacket.BUFFER_SIZE];
packet.Pack(buffer, ref offset);
var sessionKey = new byte[16];
var sessionSalt = new byte[16];
var sessionAuth = new byte[32];
// TODO add _txRoc logic
var index = ((ulong)_txRoc << 16) + packet.SequenceNumber;
GenerateSessionKey(_txKey, _txSalt, sessionKey, sessionSalt, sessionAuth);
var sessionIv = new byte[BLOCK_SIZE];
var temp = new byte[BLOCK_SIZE];
for (var i = 0; i < 14; ++i)
{
sessionIv[i] = sessionSalt[i];
}
BufferPrimitives.SetUint32(temp, 4, packet.Ssrc);
for (var i = 4; i < 8; ++i)
{
sessionIv[i] ^= temp[i];
}
BufferPrimitives.SetVarious(temp, 8, index, 6);
for (var i = 8; i < 14; ++i)
{
sessionIv[i] ^= temp[i];
}
var keyStream = new byte[packet.Payload.Length];
var payloadOffset = offset - packet.Payload.Length;
GenerateKeyStream(sessionKey, sessionIv, keyStream);
for (var i = 0; i < packet.Payload.Length; ++i)
{
buffer[payloadOffset + i] = (byte)(packet.Payload[i] ^ keyStream[i]);
}
var hmac = new byte[HMAC_SHA1_SIZE];
BufferPrimitives.SetVarious(buffer, offset, _txRoc, 4);
CalcHmac(sessionAuth, 20, buffer, offset + 4, hmac);
BufferPrimitives.SetBytes(buffer, ref offset, hmac, 0, 10);
return(BufferPrimitives.GetBytes(buffer, 0, offset));
}
public RtpPacket.ResultCodes TryParseSrtpPacket(byte[] data, out RtpPacket packet)
{
var result = RtpPacket.TryParse(data, out packet);
if (result != RtpPacket.ResultCodes.Ok)
{
return(result);
}
var packetSize = data.Length - AUTH_TAG_SIZE;
var payloadLength = packet.Payload.Length - AUTH_TAG_SIZE;
var sessionKey = new byte[16];
var sessionSalt = new byte[16];
var sessionAuth = new byte[32];
// TODO add _rxRoc logic
var index = ((ulong)_rxRoc << 16) + packet.SequenceNumber;
GenerateSessionKey(_rxKey, _rxSalt, sessionKey, sessionSalt, sessionAuth);
var hmacData = new byte[packetSize + 4];
var hmac = new byte[HMAC_SHA1_SIZE];
Array.Copy(data, 0, hmacData, 0, packetSize);
BufferPrimitives.SetVarious(hmacData, packetSize, _rxRoc, 4);
CalcHmac(sessionAuth, 20, hmacData, packetSize + 4, hmac);
for (var i = 0; i < AUTH_TAG_SIZE; ++i)
{
if (data[packetSize + i] != hmac[i])
{
return(RtpPacket.ResultCodes.IncorrectSign);
}
}
var sessionIv = new byte[BLOCK_SIZE];
var temp = new byte[BLOCK_SIZE];
for (var i = 0; i < 14; ++i)
{
sessionIv[i] = sessionSalt[i];
}
BufferPrimitives.SetUint32(temp, 4, packet.Ssrc);
for (var i = 4; i < 8; ++i)
{
sessionIv[i] ^= temp[i];
}
BufferPrimitives.SetVarious(temp, 8, index, 6);
for (var i = 8; i < 14; ++i)
{
sessionIv[i] ^= temp[i];
}
var keyStream = new byte[payloadLength];
var payload = new byte[payloadLength];
GenerateKeyStream(sessionKey, sessionIv, keyStream);
for (var i = 0; i < payloadLength; ++i)
{
payload[i] = (byte)(packet.Payload[i] ^ keyStream[i]);
}
packet.Payload = payload;
return(RtpPacket.ResultCodes.Ok);
}