Problem - Kevin Tafuro

• Get entropy if it is available, and if it is not, fall back on cryptographically strong
random numbers (using any available entropy).
• Get data that should be highly entropic that has never passed through a pseudorandom
number generator. Note that this function is not always available and
that it will hang until enough entropy is available.
The first function, which always produces cryptographically strong randomness, has
the following signature:
unsigned char *spc_rand(unsigned char *buf, size_t b);
It places b bytes into memory, starting at the location buf, and returns buf (this is
done to minimize the chance of someone misusing the API). This function always
returns unless it causes your program to abort, which it does only if spc_rand_init( )
has never successfully returned.
The second function, which returns entropy if it is available, and otherwise produces
cryptographically strong randomness, has the following signature:
unsigned char *spc_keygen(unsigned char *buf, size_t b);
The arguments are the same as for spc_rand( ). The name change reflects the fact
that this is meant to be the function you will generally use for generating long-term
key material, unless you want to insist that key material come directly from entropy,
in which case you should use the spc_entropy( ) function. For all other uses, we recommend
using spc_rand( ).
The spc_entropy( ) function mimics the first two functions:
unsigned char *spc_entropy(unsigned char *buf, size_t b);
However, note that this function will block until it has enough entropy collected to
fill the buffer. For Windows, this function is only usable using the code in this book
if you use EGADS, as discussed in Recipe 11.8.
See Also
The functions spc_keygen( ) and spc_entropy( ) should cryptographically
postprocess (whiten) any entropy they use before outputting it, if
that’s not already done by the underlying entropy sources. Often, it
will be done for you, but it will not hurt to do it again if you are not
sure. (See Recipe 11.16 for how to do it.)
Recipes 11.8, 11.10, 11.11, 11.12, 11.13, 11.14, 11.16
574 | Chapter 11: Random Numbers
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