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BN_MOD_MUL_RECIPROCAL(3ossl) OpenSSL BN_MOD_MUL_RECIPROCAL(3ossl)
NAME
BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_free,
BN_RECP_CTX_set - modular multiplication using reciprocal
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
3.0.11 2023-09-19 BN_MOD_MUL_RECIPROCAL(3ossl)