Updated: 2022/Sep/29

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BN_rand(3)                          OpenSSL                         BN_rand(3)



NAME
       BN_rand_ex, BN_rand, BN_priv_rand_ex, BN_priv_rand, BN_pseudo_rand,
       BN_rand_range_ex, BN_rand_range, BN_priv_rand_range_ex,
       BN_priv_rand_range, BN_pseudo_rand_range - generate pseudo-random
       number

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/bn.h>

        int BN_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,
                       unsigned int strength, BN_CTX *ctx);
        int BN_rand(BIGNUM *rnd, int bits, int top, int bottom);

        int BN_priv_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,
                            unsigned int strength, BN_CTX *ctx);
        int BN_priv_rand(BIGNUM *rnd, int bits, int top, int bottom);

        int BN_rand_range_ex(BIGNUM *rnd, const BIGNUM *range, unsigned int strength,
                             BN_CTX *ctx);
        int BN_rand_range(BIGNUM *rnd, const BIGNUM *range);

        int BN_priv_rand_range_ex(BIGNUM *rnd, const BIGNUM *range, unsigned int strength,
                                  BN_CTX *ctx);
        int BN_priv_rand_range(BIGNUM *rnd, const BIGNUM *range);

       The following functions have been deprecated since OpenSSL 3.0, and can
       be hidden entirely by defining OPENSSL_API_COMPAT with a suitable
       version value, see openssl_user_macros(7):

        int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom);
        int BN_pseudo_rand_range(BIGNUM *rnd, const BIGNUM *range);

DESCRIPTION
       BN_rand_ex() generates a cryptographically strong pseudo-random number
       of bits in length and security strength at least strength bits using
       the random number generator for the library context associated with
       ctx. The function stores the generated data in rnd. The parameter ctx
       may be NULL in which case the default library context is used.  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_TOP_TWO.

       BN_rand() is the same as BN_rand_ex() except that the default library
       context is always used.

       BN_rand_range_ex() generates a cryptographically strong pseudo-random
       number rnd, of security strength at least strength bits, in the range 0
       <= rnd < range using the random number generator for the library
       context associated with ctx. The parameter ctx may be NULL in which
       case the default library context is used.

       BN_rand_range() is the same as BN_rand_range_ex() except that the
       default library context is always used.

       BN_priv_rand_ex(), BN_priv_rand(), BN_priv_rand_rand_ex() and
       BN_priv_rand_range() have the same semantics as BN_rand_ex(),
       BN_rand(), BN_rand_range_ex() 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), EVP_RAND(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 BN_pseudo_rand() and BN_pseudo_rand_range()
         functions were deprecated in OpenSSL 3.0.

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

       ⊕ The BN_rand_ex(), BN_priv_rand_ex(), BN_rand_range_ex() and
         BN_priv_rand_range_ex() functions were added in OpenSSL 3.0.

COPYRIGHT
       Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (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>.



3.0.12                            2023-10-25                        BN_rand(3)