Chapter 5 Non-Cryptographic Operations 169
Generating Random Numbers
Now that you have a random seed, you can call B_RandomUpdate. The length
argument tells Crypto-C how many bytes from the random seed buffer to use. See
“Pseudo-Random Numbers and Seed Generation” on page 92 for a discussion on how
many seed bytes to use. In this example, you will use all 256 bytes from the buffer,
even though you probably entered fewer than 256 characters at the keyboard. Once
again, it is reasonable to pass a
NULL_PTR for the surrender context, because
B_RandomUpdate is a fast function:
Call
B_RandomUpdate as many times as you wish with different seeds each time to
increase the unrepeatability of your random number generator. After each Update,
you may want to overwrite and free your seed immediately.
Step 5: Generate
When generating random bytes, you call B_GenerateRandomBytes instead of a Final
function. The function prototype in Chapter 4 of the Reference Manual calls for the
following arguments: a random algorithm object, an output buffer, the number of
bytes to generate, and a surrender context. You need to prepare a buffer before calling
B_GenerateRandomBytes:
Now you can generate some random bytes. Generating 64 bytes is quick, so you are
still safe in using a
NULL_PTR for the surrender context.
if ((status = B_RandomUpdate
(randomAlgorithm, randomSeed, randomSeedLen,
(A_SURRENDER_CTX *)NULL_PTR)) != 0)
break;
#define NUMBER_OF_RANDOM_BYTES 64
unsigned char *randomByteBuffer = NULL_PTR;
randomByteBuffer = T_malloc (NUMBER_OF_RANDOM_BYTES);
if ((status = (randomByteBuffer == NULL_PTR)) != 0)
break;
if ((status = B_GenerateRandomBytes
(randomAlgorithm, randomByteBuffer, NUMBER_OF_RANDOM_BYTES,
(A_SURRENDER_CTX *)NULL_PTR)) != 0)
break;
