1 <?xml version="1.0" encoding="utf-8"?>

     2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

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     4 "Eclipse Public License v1.0" which accompanies this distribution, 

     5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

     6 <!-- Initial Contributors:

     7     Nokia Corporation - initial contribution.

     8 Contributors: 

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    10 <!DOCTYPE task

    11   PUBLIC "-//OASIS//DTD DITA Task//EN" "task.dtd">

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

    13 RTP Packet Data</title><abstract><p/>SRTP generates SRTP packets from the RTP stream and forwards

    14 the packets to the receiver. SRTP transforms incoming SRTP packets to RTP

    15 packets and passes them up the stack. To ensure the confidentiality of the

    16 packet content, data encryption is used.  <p/> The data packet consists

    17 of payload and header. The payload is encrypted. An authentication is performed

    18 collectively on the header and the encrypted payload. <p/>  Encrypted RTP

    19 packet data is encapsulated for transmission in a single lower-layer packet

    20 as a unit. The encrypted SRTP packet consists of the encrypted RTP payload

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

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

    23 are confirmed by the receiver through header and payload validity checks. </abstract><prolog><metadata><keywords/></metadata></prolog><taskbody>

    24 <prereq><p>An SRTP session must be created and initialized before an application

    25 requests for a RTP payload encryption. </p> </prereq>

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

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

    28 for encryption of RTP packet. </cmd>

    29 </step>

    30 <step id="GUID-C38877C6-EEE0-5E63-80A2-5826F8BF826B"><cmd>The SRTP DLL checks

    31 for the cryptographic context of the input stream. If a match is not found,

    32 SRTP DLL checks for the cryptographic context of the session. </cmd>

    33 </step>

    34 <step id="GUID-BA67E90F-86E4-579F-8CC5-A6A765F73F92"><cmd/>

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

    36 of the class <xref href="GUID-8B875E75-DD09-3E4D-9FC6-152091869BA2.dita"><apiname>CSRTPSession</apiname></xref>.The session

    37 keys in the cryptographic context of the current SRTP session are used for

    38 encryption. </info>

    39 <substeps id="GUID-AF904AE9-50C8-56DF-8F58-B8642036B060">

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

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

    42 as described below. </info>

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

    44                      IMPORT_C HBufC8* ProtectRTPL(TUint aSSRC, const TDesC8& aPacket); 

    45                   </codeblock> </stepxmp>

    46 

    47 <info>This API is invoked if the session finds a match stream and protect

    48 stream. </info>

    49 <info>aSSRC is the input parameter that contains the Synchronisation Source

    50 (SSRC). Synchronisation Source is the source for stream of RTP packets identified

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

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

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

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

    55 length may lead to incorrect encryption. </stepxmp>

    56 <info>HBufC8 is the output parameter that contains the encrypted packet. </info>

    57 <stepresult>The API leaves, if a matching stream is not found. </stepresult>

    58 </substep>

    59 </substeps>

    60 </step>

    61 <step id="GUID-80D0973B-232D-5EAC-A9F3-11C039E3401A"><cmd>The SRTP DLL updates

    62 the count of packets encrypted. </cmd>

    63 </step>

    64 </steps>

    65 <result><p>On successful execution of the API, encrypted data is returned. </p> </result>

    66 </taskbody><related-links>

    67 <link href="GUID-06370120-7738-5694-9A8C-3B5B1E3A4352.dita"><linktext>Creating

    68 an SRTP                 Session</linktext></link>

    69 <link href="GUID-425A208C-5D2D-55FD-8623-9E00006E2781.dita"><linktext>Creating

    70 a                 Cryptographic Context</linktext></link>

    71 <link href="GUID-372B7A9F-261E-5F3F-B114-4BE2FE2EF7C7.dita"><linktext>Creating

    72 an SRTP                 Stream</linktext></link>

    73 <link href="GUID-79846EA2-33CD-5D01-8E96-6092C15BD839.dita"><linktext>Encrypting

    74                 RTCP Packet Data</linktext></link>

    75 <link href="GUID-6E1AC4C9-7CA3-503A-AFC0-BAF29CCA8290.dita"><linktext>Decrypting

    76 RTP                 Packet Data</linktext></link>

    77 <link href="GUID-F9A24A47-7A0B-5F6E-8B0A-B7A7BCC4EAFC.dita"><linktext>Decrypting

    78                 RTCP Packet Data</linktext></link>

    79 <link href="GUID-B9BD2E0A-F214-5344-91A6-E4E99F0D74C8.dita"><linktext>Updating

    80 Master                 Key</linktext></link>

    81 <link href="GUID-F9A24A47-7A0B-5F6E-8B0A-B7A7BCC4EAFC.dita"><linktext>Managing

    82                 Master Key</linktext></link>

    83 </related-links></task>