Bytes is unified with a list of N cryptographically secure
pseudo-random bytes. Each byte is an integer between 0 and 255. If
the internal pseudo-random number generator (PRNG) has not been
seeded with enough entropy to ensure an unpredictable byte
sequence, an exception is thrown.
One way to relate such a list of bytes to an integer is to use
CLP(FD) constraints as follows:
:- use_module(library(clpfd)).
bytes_integer(Bs, N) :-
foldl(pow, Bs, 0-0, N-_).
pow(B, N0-I0, N-I) :-
B in 0..255,
N #= N0 + B*256^I0,
I #= I0 + 1.
With this definition, you can generate a random 256-bit integer
from a list of 32 random bytes:
?- crypto_n_random_bytes(32, Bs),
bytes_integer(Bs, I).
Bs = [98, 9, 35, 100, 126, 174, 48, 176, 246|...],
I = 109798276762338328820827...(53 digits omitted).
The above relation also works in the other direction, letting you
translate an integer to a list of bytes. In addition, you can
use hex_bytes/2 to convert bytes to tokens that can be easily
exchanged in your applications. This also works if you have
compiled SWI-Prolog without support for large integers.
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