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<concept id="GUID-425A208C-5D2D-55FD-8623-9E00006E2781" xml:lang="en"><title>Creating

Cryptographic Context</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>SRTP library generates SRTP packets from the RTP or RTCP stream and forwards

the packets to the receiver. SRTP transforms incoming SRTP packets to RTP/RTCP

packets and passes them up the stack. The cryptographic state information

associated with each SRTP stream is termed the cryptographic context. The

state information is maintained by both the sender and receiver of SRTP streams. </p>

<p>A cryptographic context includes a session key used in encryption and message

authentication. A cryptographic context also includes a securely exchanged

random bit string used to derive session keys called the master key. In addition

to the session and master key the cryptographic context includes other working

session parameters. </p>

<section><title>Required background</title> <p>Prior to cryptographic context

creation: </p> <ul>

<li id="GUID-2958EA10-E760-59DE-AC4B-BE8B99CCA660"><p>The master key,master

salt and parameters (ie. TSrtpCryptoParams) required to create the cryptographic

context must be created and initalised. </p> </li>

</ul> </section>

<section><title>Procedure</title><p>The following steps describe the steps

involved in creating a cryptographic context: </p><ul>

<li id="GUID-C6379A93-A005-51B2-8CDA-49A7110C2717"><p>Create a cryptographic

context by invoking the API <xref href="GUID-E9F66C90-C0BF-3713-8BA0-810A362A1774.dita"><apiname>NewL()</apiname></xref> or <xref href="GUID-E9F66C90-C0BF-3713-8BA0-810A362A1774.dita"><apiname>NewLC()</apiname></xref> of the class <xref href="GUID-E9F66C90-C0BF-3713-8BA0-810A362A1774.dita"><apiname>CSRTPCryptoContext</apiname></xref>. </p> <ol id="GUID-13319A29-DE4C-50D3-A0F4-02C0E71986ED">

<li id="GUID-195D2061-6DF7-58CC-BEB8-F321134B0325"><p><codeblock id="GUID-13CEC739-A557-520B-8AD6-6523BCFCF1B7" xml:space="preserve">

                     IMPORT_C static CSRTPCryptoContext* NewL( const CSRTPMasterKey* aKey,

                                            const CSRTPMasterSalt* aSalt, 

                                            const TSrtpCryptoParams&amp; aCryptoParams);</codeblock> </p> <p>aKey

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

input parameter that contains the master salt key. </p> <p>aCryptoParams is

the input parameter that contains the Crypto Context parameters. </p> <p>The

API leaves with KErrNone if successfully executed, else returns a valid system-wide

error code. </p> </li>

<li id="GUID-2F0536E7-0074-52FC-BB9E-0A9A3F03B395"><p><codeblock id="GUID-3F31AFE2-9E0C-5D62-8217-861D7CE59964" xml:space="preserve">

                     IMPORT_C static CSRTPCryptoContext* NewLC( const CSRTPMasterKey* aKey,

                                            const CSRTPMasterSalt* aSalt, 

                                            const TSrtpCryptoParams&amp; aCryptoParams );</codeblock> </p> <p>aKey

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

input parameter that contains the master salt key. </p> <p>aCryptoParams is

the input parameter that contains the Crypto Context parameters. </p> <p>The

API leaves with KErrNone if successfully executed, else returns a valid system-wide

error code. </p> </li>

</ol> </li>

</ul><p><b>Creating Master Key</b></p><p> The master key can be created using

the following API's:</p><ul>

<li><codeblock xml:space="preserve">IMPORT_C static CSRTPMasterKey* NewL( const TDesC8&amp; aKey,const TDesC8&amp; aMKI,TUint aN_E = KSRTPDefSessionEncryptionKeyLength,Uint aN_A = KSRTPDefSessionAuthenticationKeyLength );</codeblock></li>

<li><codeblock xml:space="preserve">IMPORT_C static CSRTPMasterKey* NewLC( const TDesC8&amp; aKey,const TDesC8&amp; aMKI,TUint aN_E = KSRTPDefSessionEncryptionKeyLength,TUint aN_A = KSRTPDefSessionAuthenticationKeyLength);</codeblock></li>

<li><codeblock xml:space="preserve">IMPORT_C static CSRTPMasterSalt* NewLC( const TDesC8&amp; aKey, TUint aN_S = KSRTPDefSessionSaltingKeyLength );</codeblock></li>

</ul><p><b>Creating Master Salt Key</b></p><p>The master salt key can be created

using the following API's:</p><ul>

<li><codeblock xml:space="preserve">IMPORT_C static CSRTPMasterSalt* NewL( const TDesC8&amp; aKey,TUint aN_S = KSRTPDefSessionSaltingKeyLength )</codeblock></li>

</ul> </section>

<section><title>Results</title> <p>On successful execution of the API, a cryptographic

context is created. </p> <p>The cryptographic context can be used by a SRTP

session or Stream. In other words, the cryptographic context is owned by the

session or stream. </p> <p>The master keys and the master salt are always

owned by the cryptographic context. </p> </section>

<section> <p>For more information on cryptographic context management also

refer: </p> <p> <xref href="GUID-E9F66C90-C0BF-3713-8BA0-810A362A1774.dita"><apiname>MasterKey()</apiname></xref>  </p> <p> <xref href="GUID-E9F66C90-C0BF-3713-8BA0-810A362A1774.dita"><apiname>SetMasterKey()</apiname></xref>  </p> <p> <xref href="GUID-E9F66C90-C0BF-3713-8BA0-810A362A1774.dita"><apiname> MasterSalt()</apiname></xref>  </p> <p> <xref href="GUID-E9F66C90-C0BF-3713-8BA0-810A362A1774.dita"><apiname>SetMasterSalt()</apiname></xref>  </p> <p> <xref href="GUID-E9F66C90-C0BF-3713-8BA0-810A362A1774.dita"><apiname>SetRCCm3Sync()</apiname></xref>  </p> <p> <xref href="GUID-E9F66C90-C0BF-3713-8BA0-810A362A1774.dita"><apiname>CryptoParams()</apiname></xref>  </p> <p> <xref href="GUID-E9F66C90-C0BF-3713-8BA0-810A362A1774.dita"><apiname> AddCryptoChangeObserver()</apiname></xref>  </p> <p> <xref href="GUID-E9F66C90-C0BF-3713-8BA0-810A362A1774.dita"><apiname>RemoveCryptoChangeObserver()</apiname></xref>  </p> <p> <xref href="GUID-E9F66C90-C0BF-3713-8BA0-810A362A1774.dita"><apiname>UpdateCryptoParams()</apiname></xref>  </p> </section>

</conbody><related-links>

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

an SRTP                 Session</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-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>