RSA Security 5.2.2 manual Generating Random Numbers with SHA1

Generating Random Numbers

Generating Random Numbers

In the “Introductory Example” on page 9, we hard-coded the DES key. In an actual application, you would use randomly-generated values. Crypto-C allows you to generate a pseudo-random sequence of bytes using a pseudo-random number generator (PRNG). These PRNGs are based on the message digests MD2, MD5, and SHA1. This section shows how to use AI_X962Random_V0, a SHA1-based pseudo- random number generator. Its implementation can also be used as a model for the MD2 and MD5 random number generators. This model should be used for most random-number generation methods.

Note: There is also AI_X931Random, which is a SHA1-based pseudo-random number generator that allows multiple streams of randomness. It is intended primarily for use with AI_RSAStrongKeyGen, and should not be used for general-purpose random-number generation. For an example of how to use AI_X931Random, see “Putting It All Together: An X9.31 Example” on page 313.

Generating Random Numbers with SHA1

The example in this section corresponds to the file genbytes.c. This example, which uses AI_X962Random_V0, can easily be modified to use the PRNGs based on MD2 and MD5, AI_MD2Random and AI_MD5Random, respectively.

Step 1: Creating An Algorithm Object

Declare a variable to be B_ALGORITHM_OBJ. As defined in the function prototype in Chapter 4 of the Reference Manual, its address is the argument for B_CreateAlgorithmObject:

B_ALGORITHM_OBJ randomAlgorithm = (B_ALGORITHM_OBJ)NULL_PTR;

if ((status = B_CreateAlgorithmObject (&randomAlgorithm)) != 0) break;

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