# BN_rand

## Synopsis

#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); |

## DESCRIPTION

BN_rand() generates a cryptographically strong pseudo-random number
of **bits** in length and stores it in
**rnd**. If **top** is -1, the most significant bit of the
random number can be zero. If **top** is
0, it is set to 1, and if **top** is 1,
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 true, the number will be odd. The
value of **bits** must be zero or
greater. If **bits** is 1 then **top** cannot also be 1.

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).