BN_rand.pod revision 109998 
1=pod
2
3=head1 NAME
4
5BN_rand, BN_pseudo_rand - generate pseudo-random number
6
7=head1 SYNOPSIS
8
9 #include <openssl/bn.h>
10
11 int BN_rand(BIGNUM *rnd, int bits, int top, int bottom);
12
13 int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom);
14
15 int BN_rand_range(BIGNUM *rnd, BIGNUM *range);
16
17 int BN_pseudo_rand_range(BIGNUM *rnd, BIGNUM *range);
18
19=head1 DESCRIPTION
20
21BN_rand() generates a cryptographically strong pseudo-random number of
22B<bits> bits in length and stores it in B<rnd>. If B<top> is -1, the
23most significant bit of the random number can be zero. If B<top> is 0,
24it is set to 1, and if B<top> is 1, the two most significant bits of
25the number will be set to 1, so that the product of two such random
26numbers will always have 2*B<bits> length.  If B<bottom> is true, the
27number will be odd.
28
29BN_pseudo_rand() does the same, but pseudo-random numbers generated by
30this function are not necessarily unpredictable. They can be used for
31non-cryptographic purposes and for certain purposes in cryptographic
32protocols, but usually not for key generation etc.
33
34BN_rand_range() generates a cryptographically strong pseudo-random
35number B<rnd> in the range 0 <lt>= B<rnd> E<lt> B<range>.
36BN_pseudo_rand_range() does the same, but is based on BN_pseudo_rand(),
37and hence numbers generated by it are not necessarily unpredictable.
38
39The PRNG must be seeded prior to calling BN_rand() or BN_rand_range().
40
41=head1 RETURN VALUES
42
43The functions return 1 on success, 0 on error.
44The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
45
46=head1 SEE ALSO
47
48L<bn(3)|bn(3)>, L<ERR_get_error(3)|ERR_get_error(3)>, L<rand(3)|rand(3)>,
49L<RAND_add(3)|RAND_add(3)>, L<RAND_bytes(3)|RAND_bytes(3)>
50
51=head1 HISTORY
52
53BN_rand() is available in all versions of SSLeay and OpenSSL.
54BN_pseudo_rand() was added in OpenSSL 0.9.5. The B<top> == -1 case
55and the function BN_rand_range() were added in OpenSSL 0.9.6a.
56BN_pseudo_rand_range() was added in OpenSSL 0.9.6c.
57
58=cut
59