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, const BIGNUM *a, BN_RECP_CTX *recp, 19 BN_CTX *ctx); 20 21 int BN_mod_mul_reciprocal(BIGNUM *r, const BIGNUM *a, const 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 2000-2021 The OpenSSL Project Authors. All Rights Reserved. 70 71Licensed under the Apache License 2.0 (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