/**
* Perform Counter Mode AES encryption / decryption
*
* @param pkt
* the RTP packet to be encrypted / decrypted
*/
public void ProcessPacketAESCM(RawPacket pkt)
{
long ssrc = pkt.GetSSRC();
int seqNo = pkt.GetSequenceNumber();
#pragma warning disable CS0675 // Bitwise-or operator used on a sign-extended operand
long index = ((long)roc << 16) | seqNo;
#pragma warning restore CS0675 // Bitwise-or operator used on a sign-extended operand
ivStore[0] = saltKey[0];
ivStore[1] = saltKey[1];
ivStore[2] = saltKey[2];
ivStore[3] = saltKey[3];
int i;
for (i = 4; i < 8; i++)
{
ivStore[i] = (byte)((0xFF & (ssrc >> ((7 - i) * 8))) ^ this.saltKey[i]);
}
for (i = 8; i < 14; i++)
{
ivStore[i] = (byte)((0xFF & (byte)(index >> ((13 - i) * 8))) ^ this.saltKey[i]);
}
ivStore[14] = ivStore[15] = 0;
int payloadOffset = pkt.GetHeaderLength();
int payloadLength = pkt.GetPayloadLength();
cipherCtr.Process(cipher, pkt.GetBuffer(), payloadOffset, payloadLength, ivStore);
}
public byte[] Transform(byte[] pkt, int offset, int length)
{
// Updates the contents of raw packet with new incoming packet
this.rawPacket.Wrap(pkt, offset, length);
// Associate packet to a crypto context
long ssrc = rawPacket.GetSSRC();
SrtpCryptoContext context = null;
contexts.TryGetValue(ssrc, out context);
if (context == null)
{
context = forwardEngine.GetDefaultContext().deriveContext(ssrc, 0, 0);
context.DeriveSrtpKeys(0);
contexts[ssrc] = context;
}
// Transform RTP packet into SRTP
context.TransformPacket(this.rawPacket);
return(this.rawPacket.GetData());
}