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BN_mod_mul_reciprocal(3) OpenSSL BN_mod_mul_reciprocal(3) NAME BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_free, BN_RECP_CTX_set - modular multiplication using reciprocal LIBRARY libcrypto, -lcrypto 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); DESCRIPTION BN_mod_mul_reciprocal() can be used to perform an efficient BN_mod_mul(3) operation when the operation will be performed repeatedly with the same modulus. It computes r=(a*b)%m using recp=1/m, which is set as described below. ctx is a previously allocated BN_CTX used for temporary variables. BN_RECP_CTX_new() allocates and initializes a BN_RECP structure. BN_RECP_CTX_free() frees the components of the BN_RECP, and, if it was created by BN_RECP_CTX_new(), also the structure itself. If recp is NULL, nothing is done. BN_RECP_CTX_set() stores m in recp and sets it up for computing 1/m and shifting it left by BN_num_bits(m)+1 to make it an integer. The result and the number of bits it was shifted left will later be stored in recp. BN_div_recp() divides a by m using recp. It places the quotient in dv and the remainder in rem. The BN_RECP_CTX structure cannot be shared between threads. RETURN VALUES BN_RECP_CTX_new() returns the newly allocated 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 ERR_get_error(3). SEE ALSO ERR_get_error(3), BN_add(3), BN_CTX_new(3) HISTORY BN_RECP_CTX_init() was removed in OpenSSL 1.1.0 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 <https://www.openssl.org/source/license.html>. 1.1.1 2018-09-17 BN_mod_mul_reciprocal(3)