BN_mod_mul_reciprocal
Section: OpenSSL (3)
Updated: 20170525
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NAME
BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_init,
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_init(BN_RECP_CTX *recp);
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_init() initializes an existing uninitialized BN_RECP.
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.
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 is defined as follows:
typedef struct bn_recp_ctx_st
{
BIGNUM N; /* the divisor */
BIGNUM Nr; /* the reciprocal */
int num_bits;
int shift;
int flags;
} BN_RECP_CTX;
It 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_init() and BN_RECP_CTX_free() have no return values.
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
bn(3),
ERR_get_error(3),
BN_add(3),
BN_CTX_new(3)
HISTORY
BN_RECP_CTX was added in SSLeay 0.9.0. Before that, the function
BN_reciprocal() was used instead, and the
BN_mod_mul_reciprocal()
arguments were different.
Index
 NAME

 SYNOPSIS

 DESCRIPTION

 RETURN VALUES

 SEE ALSO

 HISTORY
