Updated: 2022/Sep/29

Please read Privacy Policy. It's for your privacy.

BN_mod_mul_reciprocal(3)            OpenSSL           BN_mod_mul_reciprocal(3)

       BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_free,
       BN_RECP_CTX_set - modular multiplication using reciprocal

       libcrypto, -lcrypto

        #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);

       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

       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.

       BN_RECP_CTX_new() returns the newly allocated BN_RECP_CTX, and NULL on

       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).

       ERR_get_error(3), BN_add(3), BN_CTX_new(3)

       BN_RECP_CTX_init() was removed in OpenSSL 1.1.0

       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

1.1.1i                            2018-09-23          BN_mod_mul_reciprocal(3)