NAME

       BN_rand, BN_priv_rand, BN_pseudo_rand, BN_rand_range, BN_priv_rand_range,
       BN_pseudo_rand_range - generate pseudo-random number

SYNOPSIS

        #include <openssl/bn.h>

        int BN_rand(BIGNUM *rnd, int bits, int top, int bottom);

        int BN_priv_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_priv_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 bits is less than zero, or too small to accommodate 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_rand_range() generates a cryptographically strong pseudo-random number rnd in the range
       0 <= rnd < range.

       BN_priv_rand() and BN_priv_rand_range() have the same semantics as BN_rand() and
       BN_rand_range() respectively.  They are intended to be used for generating values that
       should remain private, and mirror the same difference between RAND_bytes(3) and
       RAND_priv_bytes(3).

NOTES

       Always check the error return value of these functions and do not take randomness for
       granted: an error occurs if the CSPRNG has not been seeded with enough randomness to
       ensure an unpredictable byte sequence.

RETURN VALUES

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

HISTORY

       • Starting with OpenSSL release 1.1.0, BN_pseudo_rand() has been identical to BN_rand()
         and BN_pseudo_rand_range() has been identical to BN_rand_range().  The "pseudo"
         functions should not be used and may be deprecated in a future release.

       • BN_priv_rand() and BN_priv_rand_range() were added in OpenSSL 1.1.1.

SEE ALSO

       ERR_get_error(3), RAND_add(3), RAND_bytes(3), RAND_priv_bytes(3), RAND(7), RAND_DRBG(7)

COPYRIGHT

       Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (the "License").  You may not use this file except in
       compliance with the License.  You can obtain a copy in the file LICENSE in the source
       distribution or at <https://www.openssl.org/source/license.html>.