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

<task id="GUID-B9BD2E0A-F214-5344-91A6-E4E99F0D74C8" xml:lang="en"><title>Updating

SRTP Master Key</title><abstract><p>A single master key provides keying material for confidentiality

and integrity protection of the SRTP and the corresponding SRTCP stream. </p>The

SRTP master key is updated in the two circumstances: <ul>

<li><p>For each master key, a record of number of packets processed sent is

maintained. There is a limit on the number of packets processed that can be

processed by a single master key. During encryption or decryption of the RTP/RTCP

packets, the SRTP stack checks for the number of packets processed. If the

number of packets processed, ha s reached the maximum permisible value , the

master key status is identified as stale. The SRTP notifies the SRTP client

of the master key status. The SRTP client may decide to update the master

key in response to the notification.</p></li>

<li><p>The SRTP client may update the master key for robust security, prior

to master key stale status identification. </p></li>

</ul></abstract><prolog><metadata><keywords/></metadata></prolog><taskbody>

<prereq><p>An SRTP session must be created and initialized. </p> </prereq>

<steps id="GUID-2D939DEF-AA2A-598B-89FD-F6AD290344A0">

<step id="GUID-39FD589D-DFD0-5F7A-BABE-547CD59F295F"><cmd/>

<info>The SRTP client receives notification of master key stale state or SRTP

client decides to update the master key for security. </info>

</step>

<step id="GUID-E9C74070-5634-5659-83D5-ECB3595502C0"><cmd>The SRTP client

updates the master key using the <xref href="GUID-A2B842EC-936F-3805-8365-C1F9BE20832E.dita"><apiname>SetMasterKey()</apiname></xref> API of

the class <xref href="GUID-E9F66C90-C0BF-3713-8BA0-810A362A1774.dita"><apiname>CSRTPCryptoContext</apiname></xref>. </cmd>

<substeps id="GUID-081E7F1B-DDDB-52B1-BE60-FE80F0FCBCF0">

<substep id="GUID-6C510541-566D-528A-AC11-DE99D0B51F49"><cmd/>

<info>The prototype of the API is as described below: </info>

<info><ul>

<li id="GUID-D95A74D0-6189-5C1A-B3DF-53994DB83EB2"><codeblock id="GUID-F4B29F0D-1299-53CE-821C-B1C387C50B77" xml:space="preserve">IMPORT_C void SetMasterKey( const CSRTPMasterKey* aKey);

                  </codeblock> <p>This API updates

the master key. </p> <p>aKey is the input parameter that contains the new

master key. </p> </li>

</ul> </info>

</substep>

</substeps>

</step>

</steps>

<result><p>A new master key is returned to the stream or session. </p> <p>SRTP

implementation derives new session keys from the new master key. </p> <p>SRTP

client updates the stream/session cryptographic context with a the new master

key. </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-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-F9A24A47-7A0B-5F6E-8B0A-B7A7BCC4EAFC.dita"><linktext>Managing

                Master Key</linktext></link>

</related-links></task>