Generating Random Numbers
166 RSA BSAFE Crypto-C Developer’s Guide
Step 2: Setting The Algorithm Object
You need to supply an appropriate algorithm info type (AI) and the proper associated
info
to B_SetAlgorithmInfo. For random-number generation, you have a choice
between
AI_MD2Random, AI_MD5Random, AI_X962Random_V0 (also known as
AI_SHA1Random), and AI_X931Random, based on the message digest algorithms MD2,
MD5, and SHA1 described earlier. For this example, choose
AI_X962Random_V0.
Note:
AI_SHA1Random is identical to AI_X962Random_V0; the name AI_SHA1Random is
used in the demo applications. However,
AI_SHA1Random may change in
future versions of Crypto-C. For forward compatibility, we recommend that
you do not use the name
AI_SHA1Random in your applications; use
AI_X962Random_V0 instead.
Recent cryptanalytic work has discovered a collision in MD2’s internal
compression function, and there is some chance that the attack on MD2 may
be extended to the full hash function. The same attack applies to MD. Another
attack has been applied to the compression function on MD5, though this has
yet to be extended to the full MD5. RSA Security recommends that before you
use MD, MD2, or MD5, you should consult the RSA Laboratories Web site to
be sure that their use is consistent with the latest information.
The entry for
AI_SHA1Random in Chapter 2 of the Reference Manual refers you to
AI_X962Random_V0; the entry for this second AI states that the
info
supplied to
B_SetAlgorithmInfo is NULL_PTR. So the proper way to set your random algorithm
object is:
Step 3: Init
Initialize
randomAlgorithm
with B_RandomInit. The prototype of this function in
Chapter 4 of the Reference Manual indicates that it takes three arguments: the
algorithm object, the algorithm chooser, and the surrender context. The first argument
is
randomAlgorithm. For the second argument, build an algorithm chooser that
contains the AMs listed in the Reference Manual Chapter 2 entry for
AI_X962Random_V0.
B_RandomInit is a fast function, so it is reasonable to use a properly cast NULL_PTR for
the surrender context as the third argument.
if ((status = B_SetAlgorithmInfo
(randomAlgorithm, AI_SHA1Random, NULL_PTR)) != 0)
break;
