openssl/doc/man3/BN_rand.pod

=pod

=head1 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

=head1 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);

Deprecated since OpenSSL 3.0, 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);

=head1 DESCRIPTION

BN_rand_ex() generates a cryptographically strong pseudo-random
number of I<bits> in length and security strength at least I<strength> bits
using the random number generator for the library context associated with
I<ctx>. The function stores the generated data in I<rnd>. The parameter I<ctx>
may be NULL in which case the default library context is used.
If I<bits> is less than zero, or too small to
accommodate the requirements specified by the I<top> and I<bottom>
parameters, an error is returned.
The I<top> parameters specifies
requirements on the most significant bit of the generated number.
If it is B<BN_RAND_TOP_ANY>, there is no constraint.
If it is B<BN_RAND_TOP_ONE>, the top bit must be one.
If it is B<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*I<bits> length.
If I<bottom> is B<BN_RAND_BOTTOM_ODD>, the number will be odd; if it
is B<BN_RAND_BOTTOM_ANY> it can be odd or even.
If I<bits> is 1 then I<top> cannot also be B<BN_RAND_FLG_TOPTWO>.

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 I<rnd>, of security stength at least I<strength> bits,
in the range 0 E<lt>= I<rnd> E<lt> I<range> using the random number
generator for the library context associated with I<ctx>. The parameter I<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 L<RAND_bytes(3)> and L<RAND_priv_bytes(3)>.

=head1 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.

=head1 RETURN VALUES

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

=head1 SEE ALSO

L<ERR_get_error(3)>,
L<RAND_add(3)>,
L<RAND_bytes(3)>,
L<RAND_priv_bytes(3)>,
L<RAND(7)>,
L<EVP_RAND(7)>

=head1 HISTORY

=over 2

=item *

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.

=item *

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

=item *

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.

=back

=head1 COPYRIGHT

Copyright 2000-2021 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
L<https://www.openssl.org/source/license.html>.

=cut