=pod =head1 NAME BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_free, BN_RECP_CTX_set - modular multiplication using reciprocal =head1 SYNOPSIS #include <openssl/bn.h> BN_RECP_CTX *BN_RECP_CTX_new(void); void BN_RECP_CTX_free(BN_RECP_CTX *recp); int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx); int BN_div_recp(BIGNUM *dv, BIGNUM *rem, BIGNUM *a, BN_RECP_CTX *recp, BN_CTX *ctx); int BN_mod_mul_reciprocal(BIGNUM *r, BIGNUM *a, BIGNUM *b, BN_RECP_CTX *recp, BN_CTX *ctx); =head1 DESCRIPTION BN_mod_mul_reciprocal() can be used to perform an efficient L<BN_mod_mul(3)> operation when the operation will be performed repeatedly with the same modulus. It computes B<r>=(B<a>*B<b>)%B<m> using B<recp>=1/B<m>, which is set as described below. B<ctx> is a previously allocated B<BN_CTX> used for temporary variables. BN_RECP_CTX_new() allocates and initializes a B<BN_RECP> structure. BN_RECP_CTX_free() frees the components of the B<BN_RECP>, and, if it was created by BN_RECP_CTX_new(), also the structure itself. If B<recp> is NULL, nothing is done. BN_RECP_CTX_set() stores B<m> in B<recp> and sets it up for computing 1/B<m> and shifting it left by BN_num_bits(B<m>)+1 to make it an integer. The result and the number of bits it was shifted left will later be stored in B<recp>. BN_div_recp() divides B<a> by B<m> using B<recp>. It places the quotient in B<dv> and the remainder in B<rem>. The B<BN_RECP_CTX> structure cannot be shared between threads. =head1 RETURN VALUES BN_RECP_CTX_new() returns the newly allocated B<BN_RECP_CTX>, and NULL on error. BN_RECP_CTX_free() has no return value. For the other functions, 1 is returned for success, 0 on error. The error codes can be obtained by L<ERR_get_error(3)>. =head1 SEE ALSO L<ERR_get_error(3)>, L<BN_add(3)>, L<BN_CTX_new(3)> =head1 HISTORY BN_RECP_CTX_init() was removed in OpenSSL 1.1.0 =head1 COPYRIGHT Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved. Licensed under the OpenSSL license (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at L<https://www.openssl.org/source/license.html>. =cut