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<!-- Initial Contributors:+
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    Nokia Corporation - initial contribution.+
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Contributors: +
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<!DOCTYPE concept+
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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">+
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<concept id="GUID-66BBA81D-2488-50B8-8822-43AAAA139DDE" xml:lang="en"><title>Overview+
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of random number generation</title><prolog><metadata><keywords/></metadata></prolog><conbody>+
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<section id="GUID-B5BD3E1A-AFBB-5526-B5EA-8FA51A17E596"><title>Overview</title> <p>The+
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purpose of the Random Number Generation API is the generation of cryptographically+
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strong random numbers. </p> <p>Several cryptographic applications rely upon+
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the randomness, unpredictability and irreproducibility of the random number+
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generator, such as: </p> <ul>+
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<li id="GUID-15685756-F94B-508C-A08C-8F0ECBC1A4AA"><p>one-time pads </p> </li>+
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<li id="GUID-7E3ED7CE-65C3-5E8B-9FF0-139763F3E54B"><p>key generation </p> </li>+
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<li id="GUID-0C65E7E4-A3F5-5EC4-9851-4A4E3090607B"><p>random nonces </p> </li>+
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<li id="GUID-3C16304A-CDA0-5F50-9D6C-D76C2D6EA586"><p>Initialization Vectors+
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(IVs) </p> </li>+
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<li id="GUID-59F195DE-94E7-56EE-9A7D-EAB5E401DF9A"><p>salts to be hashed with+
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passwords </p> </li>+
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<li id="GUID-96B7B9D1-AB0D-5A54-9C7F-771008F354C1"><p>unique parameters in+
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signing operations. </p> </li>+
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</ul> <p>The RNG uses the <xref href="http://www.agner.org/random/" scope="external">RANROT</xref> algorithm+
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seeded by random data available on the target hardware (for instance free+
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running counters available on ARM processors). <note><p>In order to be <b>fully</b> compliant+
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with DSS (Digital Signature Standard), applications using the cryptography+
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library must supply a <xref href="http://cr.yp.to/bib/2000/-dss.pdf" scope="external">FIPS-186-2</xref> CR+
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1 compliant random number generator. The library provides a mechanism for+
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using such a random number generator if required. </p></note></p> </section>+
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<section id="GUID-9350FD0E-7F09-5D82-BB91-EC1C8D740DBD"><title>The Random+
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Number Generation API</title> <p>The diagram below shows the main classes+
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used in the RNG, which are implemented in <filepath>random.dll</filepath>.+
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For information on each class see the Cryptography API Reference material. </p> <fig id="GUID-5326D881-8795-5803-8B82-EC02C0C40226">+
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<title>              The inheritance hierarchy for the RRandomSession and+
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CSystemRandom classes            </title>+
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<image href="GUID-FD1BB5C6-A042-56C9-8F1F-B51BF9DF5389_d0e362142_href.png" placement="inline"/>+
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</fig><p><b>How to use TRandom</b> </p> <p> <codeph>TRandom</codeph> is a+
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cryptographically stong random number generator. Its declaration is: </p> <codeblock id="GUID-53D847C3-2A1A-51D8-93FA-F68EA2374551" xml:space="preserve">class TRandom+
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    {+
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public:+
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    IMPORT_C static void RandomL(TDes8&amp; aDestination);+
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    };</codeblock><note> The function <codeph>TRandom::Random()</codeph> which+
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panics rather than leaves when it cannot obtain a random number, is deprecated+
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from v9.1 onwards. </note> <p> <codeph>TRandom::RandomL()</codeph> generates+
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random bytes by first connecting to the random number generation server (using <codeph>RRandomSession</codeph>).+
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If the attempt to connect fails, <codeph>TRandom::RandomL()</codeph> leaves. </p> <p>The+
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server fills <codeph>aDestination</codeph> with randomly generated bytes up+
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to its current length (not its maximum length). If this fails, <codeph>TRandom::RandomL()</codeph> leaves.+
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If <codeph>aDestination</codeph> is 1024 or more bytes long, multiple calls+
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are made to the server. Finally, <codeph>TRandom</codeph> closes the session. </p> <p> <codeph>TRandom</codeph> can+
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be used like this: </p> <codeblock id="GUID-0472582C-D5BD-520D-848E-9989E8730851" xml:space="preserve">HBufC8* rand = HBufC8::NewLC(5);+
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TPtr8 pRand=rand-&gt;Des();+
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pRand.SetLength(5);+
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TRandom::RandomL(pRand);+
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...+
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CleanupStack::PopAndDestroy(rand);</codeblock> </section>+
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</conbody></concept>+
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