BN_RAND
Section: OpenSSL (3)
Updated: 2021-03-26
Page Index
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).
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>.