/**
* Transform a RTP packet into a SRTP packet. This method is called when a
* normal RTP packet ready to be sent.
*
* Operations done by the transformation may include: encryption, using
* either Counter Mode encryption, or F8 Mode encryption, adding
* authentication tag, currently HMC SHA1 method.
*
* Both encryption and authentication functionality can be turned off as
* long as the SRTPPolicy used in this SRTPCryptoContext is requires no
* encryption and no authentication. Then the packet will be sent out
* untouched. However this is not encouraged. If no SRTP feature is enabled,
* then we shall not use SRTP TransformConnector. We should use the original
* method (RTPManager managed transportation) instead.
*
* @param pkt
* the RTP packet that is going to be sent out
*/
public void TransformPacket(RawPacket pkt)
{
/* Encrypt the packet using Counter Mode encryption */
if (policy.EncType == SrtpPolicy.AESCM_ENCRYPTION || policy.EncType == SrtpPolicy.TWOFISH_ENCRYPTION)
{
ProcessPacketAESCM(pkt);
}
else if (policy.EncType == SrtpPolicy.AESF8_ENCRYPTION || policy.EncType == SrtpPolicy.TWOFISHF8_ENCRYPTION)
{
/* Encrypt the packet using F8 Mode encryption */
ProcessPacketAESF8(pkt);
}
/* Authenticate the packet */
if (policy.AuthType != SrtpPolicy.NULL_AUTHENTICATION)
{
AuthenticatePacketHMCSHA1(pkt, roc);
pkt.Append(tagStore, policy.AuthTagLength);
}
/* Update the ROC if necessary */
int seqNo = pkt.GetSequenceNumber();
if (seqNo == 0xFFFF)
{
roc++;
}
}
/**
* Transform a RTP packet into a SRTP packet.
* This method is called when a normal RTP packet ready to be sent.
*
* Operations done by the transformation may include: encryption, using
* either Counter Mode encryption, or F8 Mode encryption, adding
* authentication tag, currently HMC SHA1 method.
*
* Both encryption and authentication functionality can be turned off
* as long as the SRTPPolicy used in this SRTPCryptoContext is requires no
* encryption and no authentication. Then the packet will be sent out
* untouched. However this is not encouraged. If no SRTP feature is enabled,
* then we shall not use SRTP TransformConnector. We should use the original
* method (RTPManager managed transportation) instead.
*
* @param pkt the RTP packet that is going to be sent out
*/
public void TransformPacket(RawPacket pkt)
{
bool encrypt = false;
// Encrypt the packet using Counter Mode encryption
if (policy.EncType == SrtpPolicy.AESCM_ENCRYPTION || policy.EncType == SrtpPolicy.TWOFISH_ENCRYPTION)
{
ProcessPacketAESCM(pkt, sentIndex);
encrypt = true;
}
// Encrypt the packet using F8 Mode encryption
else if (policy.EncType == SrtpPolicy.AESF8_ENCRYPTION || policy.EncType == SrtpPolicy.TWOFISHF8_ENCRYPTION)
{
ProcessPacketAESF8(pkt, sentIndex);
encrypt = true;
}
int index = 0;
if (encrypt)
{
index = (int)(sentIndex | 0x80000000);
}
// Authenticate the packet
// The authenticate method gets the index via parameter and stores
// it in network order in rbStore variable.
if (policy.AuthType != SrtpPolicy.NULL_AUTHENTICATION)
{
AuthenticatePacket(pkt, index);
pkt.Append(rbStore, 4);
pkt.Append(tagStore, policy.AuthTagLength);
}
sentIndex++;
sentIndex &= (int)(~0x80000000); // clear possible overflow
}