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Comment randombytes_uniform()

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This commit is contained in:
Frank Denis 2017-07-23 19:44:07 +02:00
parent eaab512788
commit d7ecf04d68
1 changed files with 3 additions and 1 deletions
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4
src/libsodium/randombytes/randombytes.c
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@ -136,10 +136,12 @@ randombytes_uniform(const uint32_t upper_bound)
if (upper_bound < 2) { if (upper_bound < 2) {
return 0; return 0;
} }
min = (1U + ~upper_bound) % upper_bound; min = (1U + ~upper_bound) % upper_bound; /* = 2**32 mod upper_bound */
do { do {
r = randombytes_random(); r = randombytes_random();
} while (r < min); } while (r < min);
/* r is now clamped to a set whose size mod upper_bound == 0
* the worst case (2**31+1) requires ~ 2 attempts */
return r % upper_bound; return r % upper_bound;
} }