diff -r 89d6a7a84779 -r 25a17d01db0c Symbian3/PDK/Source/GUID-6E1AC4C9-7CA3-503A-AFC0-BAF29CCA8290.dita --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/Symbian3/PDK/Source/GUID-6E1AC4C9-7CA3-503A-AFC0-BAF29CCA8290.dita Fri Jan 22 18:26:19 2010 +0000 @@ -0,0 +1,94 @@ + + + + + +Decrypting +RTP Packet Data

SRTP generates SRTP packets from the RTP stream and forwards +the packets to the receiver. SRTP transforms incoming SRTP packets to RTP +packets and passes them up the stack. To ensure the confidentiality of the +packet content, data encryption is used. Encrypted RTP packet data is encapsulated +for transmission in a single lower-layer packet as a unit. The presence of +encryption and the correct usage of key are confirmed by the receiver through +header and payload validity checks.

At the receiving end, the packet +is authenticated first. Authentication is followed by is decoding the encrypted +payload. This process is known as decryption. Decryption requires a decryption +key.

 +

An SRTP session must be created and initialized before an application +requests for a RTP payload decryption.

+ +An application requests +for decryption of RTP packet. + +The SRTP DLL checks +for the cryptographic context of the input stream. If a match is not found, +SRTP DLL checks for the cryptographic context of the session. + +The SRTP DLL checks +the replay list for the packet index. If a packet with the same index is found +in the replay list the packet is dropped. + +The SRTP DLL computes +the authentication tag for the packet. The computed tag is matched with the +tag in the packet. If the tags match, the packet is accepted and the packet +index is added to the replay list. + + +The packet is decrypted using UnprotectRTPL() API +of the class CSRTPSession.The session +keys in the cryptographic context of the current SRTP session are used for +decryption. + + +The prototype for the API UnprotectRTPL() is as described +below. + + IMPORT_C HBufC8* UnprotectRTPL(TUint aSSRC, const TDesC8& aPacket); + + +This API is invoked if the session finds a match stream and unprotect +stream. +aSSRC is the input parameter that contains the Synchronisation Source +(SSRC). Synchronisation Source is the source of the stream of RTP packets +identified by a 32 bit numeric. SSRC identifier is a part of the RTP packet +header. +aPacket is the input parameter that contains packet to be unprotected. +The length of descriptor should match the actual data length. A mismatch in +the length descriptor and actual length may lead to incorrect encryption. +HBufC8 is the output parameter that contains the decrypted packet. +

The API leaves, if matching stream is not found.

In +late binding cases, the API tries to find a stream with SSRC is equal to zero +and unprotect the packet.

+ + + +The SRTP DLL updates +the count of packets decrypted. + + +

On successful execution of the API, decrypted data is returned.

If +any of the above mentioned checks fail, the packet is discarded.

+ +Creating +an SRTP Session +Creating +a Cryptographic Context +Creating +an SRTP Stream +Encrypting + RTCP Packet Data +Encrypting +RTP Packet Data +Decrypting + RTCP Packet Data +Updating +Master Key +Managing + Master Key + \ No newline at end of file