BN_rand.3ssl man page

BN_rand, BN_pseudo_rand, BN_rand_range, BN_pseudo_rand_range — generate pseudo-random number


#include <openssl/bn.h>
int BN_rand(BIGNUM *rnd, int bits, int top, int bottom);
int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom);
int BN_rand_range(BIGNUM *rnd, BIGNUM *range);
int BN_pseudo_rand_range(BIGNUM *rnd, BIGNUM *range);


BN_rand() generates a cryptographically strong pseudo-random number of bits in length and stores it in rnd. If bits is less than zero, or too small to accomodate the requirements specified by the top and bottom parameters, an error is returned. The top parameters specifies requirements on the most significant bit of the generated number. If it is BN_RAND_TOP_ANY, there is no constraint. If it is BN_RAND_TOP_ONE, the top bit must be one. If it is BN_RAND_TOP_TWO, the two most significant bits of the number will be set to 1, so that the product of two such random numbers will always have 2*bits length. If bottom is BN_RAND_BOTTOM_ODD, the number will be odd; if it is BN_RAND_BOTTOM_ANY it can be odd or even. If bits is 1 then top cannot also be BN_RAND_FLG_TOPTWO.

BN_pseudo_rand() does the same, but pseudo-random numbers generated by this function are not necessarily unpredictable. They can be used for non-cryptographic purposes and for certain purposes in cryptographic protocols, but usually not for key generation etc.

BN_rand_range() generates a cryptographically strong pseudo-random number rnd in the range 0 <= rnd < range. BN_pseudo_rand_range() does the same, but is based on BN_pseudo_rand(), and hence numbers generated by it are not necessarily unpredictable.

The PRNG must be seeded prior to calling BN_rand() or BN_rand_range().

Return Values

The functions return 1 on success, 0 on error. The error codes can be obtained by ERR_get_error(3).

See Also

bn(3), ERR_get_error(3), rand(3), RAND_add(3), RAND_bytes(3)


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