openssl/doc/crypto/BN_rand.pod

=pod

=head1 NAME

BN_rand, BN_pseudo_rand - generate pseudo-random number

=head1 SYNOPSIS

 #include <openssl/bn.h>

 int BN_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_pseudo_rand_range(BIGNUM *rnd, BIGNUM *range);

=head1 DESCRIPTION

BN_rand() generates a cryptographically strong pseudo-random number of
B<bits> bits in length and stores it in B<rnd>. If B<top> is -1, the
most significant bit of the random number can be zero. If B<top> is 0,
it is set to 1, and if B<top> is 1, 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 true, the
number will be odd. The value of B<bits> must be zero or greater. If B<bits> is
1 then B<top> cannot also be 1.

BN_pseudo_rand() does the same, but pseudo-random numbers generated by
this function are not necessarily unpredictable. They can be used for
non-cryptographic purposes and for certain purposes in cryptographic
protocols, but usually not for key generation etc.

BN_rand_range() generates a cryptographically strong pseudo-random
number B<rnd> in the range 0 <lt>= B<rnd> E<lt> B<range>.
BN_pseudo_rand_range() does the same, but is based on BN_pseudo_rand(),
and hence numbers generated by it are not necessarily unpredictable.

The PRNG must be seeded prior to calling BN_rand() or BN_rand_range().

=head1 RETURN VALUES

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

=head1 SEE ALSO

L<bn(3)|bn(3)>, L<ERR_get_error(3)|ERR_get_error(3)>, L<rand(3)|rand(3)>,
L<RAND_add(3)|RAND_add(3)>, L<RAND_bytes(3)|RAND_bytes(3)>

=head1 HISTORY

BN_rand() is available in all versions of SSLeay and OpenSSL.
BN_pseudo_rand() was added in OpenSSL 0.9.5. The B<top> == -1 case
and the function BN_rand_range() were added in OpenSSL 0.9.6a.
BN_pseudo_rand_range() was added in OpenSSL 0.9.6c.

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