BN_add(3) — Subroutines

NAME

BN_add, BN_sub, BN_mul, BN_div, BN_sqr, BN_mod, BN_mod_mul, BN_exp, BN_mod_exp, BN_gcd − Arithmetic operations on BIGNUMs

SYNOPSIS

#include <openssl/bn.h>
int BN_add(
        BIGNUM ∗r, const BIGNUM ∗a, const BIGNUM ∗b ); int BN_sub(
        BIGNUM ∗r, const BIGNUM ∗a, const BIGNUM ∗b ); int BN_mul(
        BIGNUM ∗r, BIGNUM ∗a, BIGNUM ∗b, BN_CTX ∗ctx ); int BN_div(
        BIGNUM ∗dv, BIGNUM ∗rem, const BIGNUM ∗a, const BIGNUM ∗d,           BN_CTX ∗ctx ); int BN_sqr(
        BIGNUM ∗r, BIGNUM ∗a, BN_CTX ∗ctx ); int BN_mod(
        BIGNUM ∗rem, const BIGNUM ∗a, const BIGNUM ∗m, BN_CTX ∗ctx ); int BN_mod_mul(
        BIGNUM ∗ret, BIGNUM ∗a, BIGNUM ∗b, const BIGNUM ∗m, BN_CTX ∗ctx ); int BN_exp(
        BIGNUM ∗r, BIGNUM ∗a, BIGNUM ∗p, BN_CTX ∗ctx ); int BN_mod_exp(
        BIGNUM ∗r, BIGNUM ∗a, const BIGNUM ∗p, const BIGNUM ∗m, BN_CTX ∗ctx ); int BN_gcd(
        BIGNUM ∗r, BIGNUM ∗a, BIGNUM ∗b, BN_CTX ∗ctx );

DESCRIPTION

The BN_add() function adds a and b and places the result in r (r=a+b). The r value can be the same BIGNUM as a or b.

The BN_sub() function subtracts b from a and places the result in r (r=a-b).

The BN_mul() function multiplies a and b and places the result in r (r=a∗b). The r value may be the same BIGNUM as a or b. For multiplication by powers of 2, use the BN_lshift() function.

The BN_div() function divides a by d and places the result in dv and the remainder in rem (dv=a/d, rem=a%d). Either of dv and rem may be NULL, in which case the respective value is not returned. For division by powers of 2, use the BN_rshift() function.

The BN_sqr() function takes the square of a and places the result in r (r=a^2). The r and a values may be the same BIGNUM. This function is faster than BN_mul(r,a,a).

The BN_mod() function finds the remainder of a divided by m and places it in rem (rem=a%m).

The BN_mod_mul() function multiplies a by b and finds the remainder when divided by m (r=(a∗b)%m). The r value may be the same BIGNUM as a or b. For a more efficient algorithm, see BN_mod_mul_montgomery(3); for repeated computations using the same modulus, see BN_mod_mul_reciprocal(3).

The BN_exp() function raises a to the p power and places the result in r (r=a^p). This function is faster than repeated applications of BN_mul().

BN_mod_exp() computes a to the p power modulo m (r=a^p % m). This function uses less time and space than BN_exp().

BN_gcd() computes the greatest common divisor of a and b and places the result in r. The r value may be the same BIGNUM as a or b.

For all functions, ctx is a previously allocated BN_CTX used for temporary variables. See BN_CTX_new(3).

Unless noted otherwise, the result BIGNUM must be different from the arguments.

RETURN VALUES

For all functions, 1 is returned for success, 0 on error. The return value should always be checked (e.g., if (!BN_add(r,a,b)) goto err;). The error codes can be obtained by using the ERR_get_error() function.

HISTORY

The BN_add(), BN_sub(), BN_div(), BN_sqr(), BN_mod(), BN_mod_mul(), BN_mod_exp(), and BN_gcd() are available in all versions of SSLeay and OpenSSL. The ctx argument to BN_mul() was added in SSLeay 0.9.1b. The BN_exp() function appeared in SSLeay 0.9.0.

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