=pod

=head1 NAME

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

=head1 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);

=head1 DESCRIPTION

BN_rand() generates a cryptographically strong pseudo-random number of
B<bits> in length and stores it in B<rnd>.
If B<bits> is less than zero, or too small to
accommodate the requirements specified by the B<top> and B<bottom>
parameters, an error is returned.
The B<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*B<bits> length.
If B<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 B<bits> is 1 then B<top> cannot also be B<BN_RAND_FLG_TOPTWO>.

BN_rand_range() generates a cryptographically strong pseudo-random
number B<rnd> in the range 0 E<lt>= B<rnd> E<lt> B<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 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<RAND_DRBG(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 "pseudo" functions should not be used and may be deprecated in
a future release.

=item *

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

=back

=head1 COPYRIGHT

Copyright 2000-2019 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
