Problem - Kevin Tafuro

See Also
Recipes 11.16, 11.18, 11.19
11.2 Using a Generic API for Randomness and
Entropy
Problem
You would like to have a standard API for getting cryptographic randomness or
entropy, which you can then bind to any underlying implementation. Many recipes
in this book rely on random numbers and use the API in this recipe without concern
for what implementation is behind it.
Solution
The API in this recipe is exactly what you need. In this recipe, we show the API and
how to use it. In the next few recipes, we discuss how to bind it to third-party randomness
infrastructures.
Discussion
At an API level, this recipe is only going to look at how to fill a buffer with random
bytes. To get random values for other data types, see Recipes 11.10 through 11.14.
Here we are going to build a random number generation API where there is only a
single generator per application, or perhaps even a single generator for the entire
machine. Either way, we expect that the application will have to initialize the API.
Note that the initialization may need to seed a cryptographic pseudo-random number
generator, so the initialization part might hang. If that is a problem, launch a
thread to call the initialization routine, but be aware that asking for any cryptographically
strong pseudo-random numbers at all will cause your program to abort if the
system has not been initialized. The initialization routine is simply:
void spc_rand_init(void);
Because we know well that people will often forget to perform initialization, implementations
of this API should automatically check to see if this routine has been
called when using other API calls, and call it at that point if not.
After initialization, we will provide two universally available options for reading
data, as well as a third option that will not always be available:
• Get cryptographically strong random numbers, as generated from a well-seeded
pseudo-random number generator.
Using a Generic API for Randomness and Entropy | 573
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