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<task id="GUID-922F292E-9420-593B-B226-2764C5F29DF9" xml:lang="en"><title>Encrypting

RTP Packet Data</title><abstract><p/>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.  <p/> 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 RTP payload

and RTP header. The encrypted packet may be the exact size of the plain packet

or larger. <p/>  The presence of encryption and the correct usage of key

are confirmed by the receiver through header and 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 RTP payload encryption. </p> </prereq>

<steps id="GUID-7A30F5A3-7CDF-5ED2-92E8-9254446B17FD">

<step id="GUID-6F92FF92-7551-5AB0-B7DD-F8DD0866D35D"><cmd>An application requests

for encryption of RTP packet. </cmd>

</step>

<step id="GUID-C38877C6-EEE0-5E63-80A2-5826F8BF826B"><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-BA67E90F-86E4-579F-8CC5-A6A765F73F92"><cmd/>

<info>The packet is encrypted using <xref href="GUID-8B875E75-DD09-3E4D-9FC6-152091869BA2.dita"><apiname>ProtectRTPL()</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-AF904AE9-50C8-56DF-8F58-B8642036B060">

<substep id="GUID-5DE97C1A-88FB-5982-A675-AA9BC2ACF08B"><cmd/>

<info>The prototype for the API <xref href="GUID-8B875E75-DD09-3E4D-9FC6-152091869BA2.dita"><apiname>ProtectRTPL()</apiname></xref> is

as described below. </info>

<stepxmp><codeblock id="GUID-171C1A63-8839-55D6-863A-5149EA60BB4C" xml:space="preserve">

                     IMPORT_C HBufC8* ProtectRTPL(TUint aSSRC, const TDesC8& 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 stream of RTP packets identified

by a 32 bit numeric. SSRC identifier is a part of the RTP packet header. </info>

<stepxmp>aPacket is the input parameter that contains the packet to be protected(encrypted).

The packet includes RTP header and the paleout. The length of descriptor should

match the actual data length. A mismatch in the length descriptor and actual

length may lead to incorrect encryption. </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-80D0973B-232D-5EAC-A9F3-11C039E3401A"><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-79846EA2-33CD-5D01-8E96-6092C15BD839.dita"><linktext>Encrypting

                RTCP 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>