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<!DOCTYPE task
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<task id="GUID-79846EA2-33CD-5D01-8E96-6092C15BD839" xml:lang="en"><title>Encrypting
RTCP Packet Data</title><abstract><p/>SRTP generates SRTP packets from the RTCP stream and forwards
the SRTP packets to the receiver. SRTP transforms incoming SRTP packets to
RTCP packets and passes them up the stack. To ensure the confidentiality of
the packet content, data encryption is used.   The data packet consists of
payload and header. The payload is encrypted. An authentication is performed
collectively on the header and the encrypted payload.  <p/> Encrypted RTP
packet data is encapsulated for transmission in a single lower-layer packet
as a unit. The encrypted SRTP packet consists of the encrypted RTCP payload
and the RTCP header.<p/> The encrypted packet may be of the exact size
of the plain packet or larger.   The presence of encryption and the correct
usage of key are confirmed by the receiver through header or payload validity
checks. </abstract><prolog><metadata><keywords/></metadata></prolog><taskbody>
<prereq><p>An SRTP session must be created and initialized before an application
requests for a RTCP payload encryption. </p> </prereq>
<steps id="GUID-DB707C22-6AE1-57C7-B584-6E6471713908">
<step id="GUID-63121005-568C-5ECD-9AFC-973D3373D603"><cmd>An application requests
for encryption of RTCP packet. </cmd>
</step>
<step id="GUID-45ADDDBA-8EB1-5305-ACE3-DCA4470A93AE"><cmd>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. </cmd>
</step>
<step id="GUID-70FA5B7F-C7B6-5BEA-AAAD-657E1A5E1E26"><cmd/>
<info>The packet is encrypted using <xref href="GUID-8B875E75-DD09-3E4D-9FC6-152091869BA2.dita"><apiname>ProtectRTCPL()</apiname></xref> API
of the class <xref href="GUID-8B875E75-DD09-3E4D-9FC6-152091869BA2.dita"><apiname>CSRTPSession</apiname></xref>.The session
keys in the cryptographic context of the current SRTP session are used for
encryption. </info>
<substeps id="GUID-9DA7C40D-62AB-5196-96C7-C48263ADD28A">
<substep id="GUID-F5E4B54A-0FFE-570B-B701-518B916BACC5"><cmd/>
<info>The prototype for the API<codeph> ProtectRTCPL()</codeph> is
as described below. </info>
<stepxmp><codeblock id="GUID-7F124E08-5D8C-5BCC-B35C-02A483ECC44D" xml:space="preserve">
                     IMPORT_C HBufC8* ProtectRTCPL(TUint aSSRC, const TDesC8&amp; aPacket); 
                  </codeblock> </stepxmp>

<info>This API is invoked if the session finds a match stream and protect
stream. </info>
<info>aSSRC is the input parameter that contains the Synchronisation Source
(SSRC). Synchronisation Source is the source for the stream of RTP packets
identified by a 32 bit numeric. SSRC identifier is a part of the RTCP packet
header. </info>
<stepxmp>aPacket is the input parameter that contains the packet to be protected.
The packet includes RTP header and the paleout. The length of descriptor should
match the actual data. A mismatch in the length descriptor and actual length
may lead to incorrect encryption. The packet includes RTP header and the paleout. </stepxmp>
<info>HBufC8 is the output parameter that contains the encrypted packet. </info>
<stepresult>The API leaves, if a matching stream is not found. </stepresult>
</substep>
</substeps>
</step>
<step id="GUID-C573A38B-21BD-5F9F-BED0-729DD7CA7996"><cmd>The SRTP DLL updates
the count of packets encrypted. </cmd>
</step>
</steps>
<result><p>On successful execution of the API, encrypted data is returned. </p> </result>
</taskbody><related-links>
<link href="GUID-06370120-7738-5694-9A8C-3B5B1E3A4352.dita"><linktext>Creating
an SRTP                 Session</linktext></link>
<link href="GUID-425A208C-5D2D-55FD-8623-9E00006E2781.dita"><linktext>Creating
a                 Cryptographic Context</linktext></link>
<link href="GUID-372B7A9F-261E-5F3F-B114-4BE2FE2EF7C7.dita"><linktext>Creating
an SRTP                 Stream</linktext></link>
<link href="GUID-922F292E-9420-593B-B226-2764C5F29DF9.dita"><linktext>Encrypting
RTP                 Packet Data</linktext></link>
<link href="GUID-6E1AC4C9-7CA3-503A-AFC0-BAF29CCA8290.dita"><linktext>Decrypting
RTP                 Packet Data</linktext></link>
<link href="GUID-F9A24A47-7A0B-5F6E-8B0A-B7A7BCC4EAFC.dita"><linktext>Decrypting
                RTCP Packet Data</linktext></link>
<link href="GUID-B9BD2E0A-F214-5344-91A6-E4E99F0D74C8.dita"><linktext>Updating
Master                 Key</linktext></link>
<link href="GUID-F9A24A47-7A0B-5F6E-8B0A-B7A7BCC4EAFC.dita"><linktext>Managing
                Master Key</linktext></link>
</related-links></task>