1=pod
2
3=head1 NAME
4
5BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new,
6BN_RECP_CTX_free, BN_RECP_CTX_set - modular multiplication using
7reciprocal
8
9=head1 SYNOPSIS
10
11 #include <openssl/bn.h>
12
13 BN_RECP_CTX *BN_RECP_CTX_new(void);
14 void BN_RECP_CTX_free(BN_RECP_CTX *recp);
15
16 int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx);
17
18 int BN_div_recp(BIGNUM *dv, BIGNUM *rem, BIGNUM *a, BN_RECP_CTX *recp,
19                 BN_CTX *ctx);
20
21 int BN_mod_mul_reciprocal(BIGNUM *r, BIGNUM *a, BIGNUM *b,
22                           BN_RECP_CTX *recp, BN_CTX *ctx);
23
24=head1 DESCRIPTION
25
26BN_mod_mul_reciprocal() can be used to perform an efficient
27L<BN_mod_mul(3)> operation when the operation will be performed
28repeatedly with the same modulus. It computes B<r>=(B<a>*B<b>)%B<m>
29using B<recp>=1/B<m>, which is set as described below.  B<ctx> is a
30previously allocated B<BN_CTX> used for temporary variables.
31
32BN_RECP_CTX_new() allocates and initializes a B<BN_RECP> structure.
33
34BN_RECP_CTX_free() frees the components of the B<BN_RECP>, and, if it
35was created by BN_RECP_CTX_new(), also the structure itself.
36If B<recp> is NULL, nothing is done.
37
38BN_RECP_CTX_set() stores B<m> in B<recp> and sets it up for computing
391/B<m> and shifting it left by BN_num_bits(B<m>)+1 to make it an
40integer. The result and the number of bits it was shifted left will
41later be stored in B<recp>.
42
43BN_div_recp() divides B<a> by B<m> using B<recp>. It places the quotient
44in B<dv> and the remainder in B<rem>.
45
46The B<BN_RECP_CTX> structure cannot be shared between threads.
47
48=head1 RETURN VALUES
49
50BN_RECP_CTX_new() returns the newly allocated B<BN_RECP_CTX>, and NULL
51on error.
52
53BN_RECP_CTX_free() has no return value.
54
55For the other functions, 1 is returned for success, 0 on error.
56The error codes can be obtained by L<ERR_get_error(3)>.
57
58=head1 SEE ALSO
59
60L<ERR_get_error(3)>, L<BN_add(3)>,
61L<BN_CTX_new(3)>
62
63=head1 HISTORY
64
65BN_RECP_CTX_init() was removed in OpenSSL 1.1.0
66
67=head1 COPYRIGHT
68
69Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
70
71Licensed under the OpenSSL license (the "License").  You may not use
72this file except in compliance with the License.  You can obtain a copy
73in the file LICENSE in the source distribution or at
74L<https://www.openssl.org/source/license.html>.
75
76=cut
77