BN_rand.pod revision 306195 
1=pod
2
3=head1 NAME
4
5BN_rand, BN_pseudo_rand, BN_rand_range, BN_pseudo_rand_range - 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> in length and stores it in B<rnd>.
23If B<bits> is less than zero, or too small to
24accomodate the requirements specified by the B<top> and B<bottom>
25parameters, an error is returned.
26If B<top> is -1, the
27most significant bit of the random number can be zero. If B<top> is 0,
28it is set to 1, and if B<top> is 1, the two most significant bits of
29the number will be set to 1, so that the product of two such random
30numbers will always have 2*B<bits> length.  If B<bottom> is true, the
31number will be odd. The value of B<bits> must be zero or greater. If B<bits> is
321 then B<top> cannot also be 1.
33
34BN_pseudo_rand() does the same, but pseudo-random numbers generated by
35this function are not necessarily unpredictable. They can be used for
36non-cryptographic purposes and for certain purposes in cryptographic
37protocols, but usually not for key generation etc.
38
39BN_rand_range() generates a cryptographically strong pseudo-random
40number B<rnd> in the range 0 E<lt>= B<rnd> E<lt> B<range>.
41BN_pseudo_rand_range() does the same, but is based on BN_pseudo_rand(),
42and hence numbers generated by it are not necessarily unpredictable.
43
44The PRNG must be seeded prior to calling BN_rand() or BN_rand_range().
45
46=head1 RETURN VALUES
47
48The functions return 1 on success, 0 on error.
49The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
50
51=head1 SEE ALSO
52
53L<bn(3)|bn(3)>, L<ERR_get_error(3)|ERR_get_error(3)>, L<rand(3)|rand(3)>,
54L<RAND_add(3)|RAND_add(3)>, L<RAND_bytes(3)|RAND_bytes(3)>
55
56=head1 HISTORY
57
58BN_rand() is available in all versions of SSLeay and OpenSSL.
59BN_pseudo_rand() was added in OpenSSL 0.9.5. The B<top> == -1 case
60and the function BN_rand_range() were added in OpenSSL 0.9.6a.
61BN_pseudo_rand_range() was added in OpenSSL 0.9.6c.
62
63=cut
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