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 recip‐
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,
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
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
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 */
It cannot be shared between threads.
RETURN VALUESBN_RECP_CTX_new() returns the newly allocated BN_RECP_CTX, and NULL on
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() argu‐
ments were different.
0.9.7d 2003-11-20 BN_mod_mul_reciprocal(3)