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_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);
DESCRIPTIONBN_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 VALUESBN_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 ALSObn(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.
25/Sep/2002 0.9.6j BN_mod_mul_reciprocal(3)
