1BN_MOD_MUL_RECIPROCAL(3ossl)        OpenSSL       BN_MOD_MUL_RECIPROCAL(3ossl)
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NAME

6       BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_free,
7       BN_RECP_CTX_set - modular multiplication using reciprocal
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SYNOPSIS

10        #include <openssl/bn.h>
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12        BN_RECP_CTX *BN_RECP_CTX_new(void);
13        void BN_RECP_CTX_free(BN_RECP_CTX *recp);
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15        int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx);
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17        int BN_div_recp(BIGNUM *dv, BIGNUM *rem, const BIGNUM *a, BN_RECP_CTX *recp,
18                        BN_CTX *ctx);
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20        int BN_mod_mul_reciprocal(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
21                                  BN_RECP_CTX *recp, BN_CTX *ctx);
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DESCRIPTION

24       BN_mod_mul_reciprocal() can be used to perform an efficient
25       BN_mod_mul(3) operation when the operation will be performed repeatedly
26       with the same modulus. It computes r=(a*b)%m using recp=1/m, which is
27       set as described below.  ctx is a previously allocated BN_CTX used for
28       temporary variables.
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30       BN_RECP_CTX_new() allocates and initializes a BN_RECP structure.
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32       BN_RECP_CTX_free() frees the components of the BN_RECP, and, if it was
33       created by BN_RECP_CTX_new(), also the structure itself.  If recp is
34       NULL, nothing is done.
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36       BN_RECP_CTX_set() stores m in recp and sets it up for computing 1/m and
37       shifting it left by BN_num_bits(m)+1 to make it an integer. The result
38       and the number of bits it was shifted left will later be stored in
39       recp.
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41       BN_div_recp() divides a by m using recp. It places the quotient in dv
42       and the remainder in rem.
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44       The BN_RECP_CTX structure cannot be shared between threads.
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RETURN VALUES

47       BN_RECP_CTX_new() returns the newly allocated BN_RECP_CTX, and NULL on
48       error.
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50       BN_RECP_CTX_free() has no return value.
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52       For the other functions, 1 is returned for success, 0 on error.  The
53       error codes can be obtained by ERR_get_error(3).
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SEE ALSO

56       ERR_get_error(3), BN_add(3), BN_CTX_new(3)
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HISTORY

59       BN_RECP_CTX_init() was removed in OpenSSL 1.1.0
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62       Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
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64       Licensed under the Apache License 2.0 (the "License").  You may not use
65       this file except in compliance with the License.  You can obtain a copy
66       in the file LICENSE in the source distribution or at
67       <https://www.openssl.org/source/license.html>.
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713.1.1                             2023-08-31      BN_MOD_MUL_RECIPROCAL(3ossl)
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