Updated: 2021/Apr/14


BN_rand(3)                          OpenSSL                         BN_rand(3)



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

LIBRARY
       libcrypto, -lcrypto

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).

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

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.

       ⊕ The BN_priv_rand() and BN_priv_rand_range() functions were added in
         OpenSSL 1.1.1.

COPYRIGHT
       Copyright 2000-2019 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>.



1.1.1i                            2019-06-09                        BN_rand(3)