Overview +of random number generation

Overview

The +purpose of the Random Number Generation API is the generation of cryptographically +strong random numbers.

Several cryptographic applications rely upon +the randomness, unpredictability and irreproducibility of the random number +generator, such as:

one-time pads
key generation
random nonces
Initialization Vectors +(IVs)
salts to be hashed with +passwords
unique parameters in +signing operations.

The RNG uses the RANROT algorithm +seeded by random data available on the target hardware (for instance free +running counters available on ARM processors).

In order to be fully compliant +with DSS (Digital Signature Standard), applications using the cryptography +library must supply a FIPS-186-2 CR +1 compliant random number generator. The library provides a mechanism for +using such a random number generator if required.

The Random +Number Generation API

The diagram below shows the main classes +used in the RNG, which are implemented in random.dll. +For information on each class see the Cryptography API Reference material.

+ The inheritance hierarchy for the RRandomSession and +CSystemRandom classes + +

How to use TRandom

TRandom is a +cryptographically stong random number generator. Its declaration is:

class TRandom + { +public: + IMPORT_C static void RandomL(TDes8& aDestination); + }; The function TRandom::Random() which +panics rather than leaves when it cannot obtain a random number, is deprecated +from v9.1 onwards.

TRandom::RandomL() generates +random bytes by first connecting to the random number generation server (using RRandomSession). +If the attempt to connect fails, TRandom::RandomL() leaves.

The +server fills aDestination with randomly generated bytes up +to its current length (not its maximum length). If this fails, TRandom::RandomL() leaves. +If aDestination is 1024 or more bytes long, multiple calls +are made to the server. Finally, TRandom closes the session.

TRandom can +be used like this:

HBufC8* rand = HBufC8::NewLC(5); +TPtr8 pRand=rand->Des(); +pRand.SetLength(5); +TRandom::RandomL(pRand); +... +CleanupStack::PopAndDestroy(rand);