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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, const BIGNUM *a, BN_RECP_CTX *recp,
                        BN_CTX *ctx);

        int BN_mod_mul_reciprocal(BIGNUM *r, const BIGNUM *a, const 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 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (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>.



3.0.12                            2023-05-07          BN_mod_mul_reciprocal(3)