BN_mod_exp (3)

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(The comments found at the beginning of the groff file "man3/BN_mod_exp.3ssl".)

NAME

BN_add, BN_sub, BN_mul, BN_sqr, BN_div, BN_mod, BN_nnmod, BN_mod_add, BN_mod_sub, BN_mod_mul, BN_mod_sqr, 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_sqr(BIGNUM *r, BIGNUM *a, BN_CTX *ctx);

 int BN_div(BIGNUM *dv, BIGNUM *rem, const BIGNUM *a, const BIGNUM *d,
         BN_CTX *ctx);

 int BN_mod(BIGNUM *rem, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx);

 int BN_nnmod(BIGNUM *r, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx);

 int BN_mod_add(BIGNUM *r, BIGNUM *a, BIGNUM *b, const BIGNUM *m,
         BN_CTX *ctx);

 int BN_mod_sub(BIGNUM *r, BIGNUM *a, BIGNUM *b, const BIGNUM *m,
         BN_CTX *ctx);

 int BN_mod_mul(BIGNUM *r, BIGNUM *a, BIGNUM *b, const BIGNUM *m,
         BN_CTX *ctx);

 int BN_mod_sqr(BIGNUM *r, BIGNUM *a, 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

BN_add() adds a and b and places the result in r ("r=a+b"). r may be the same as a or b.

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

BN_mul() multiplies a and b and places the result in r ("r=a*b"). r may be the same

as a or b. For multiplication by powers of 2, use BN_lshift(3).

BN_sqr() takes the square of a and places the result in r ("r=a^2"). r and a may be the same

. This function is faster than BN_mul(r,a,a).

BN_div() 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

, in which case the respective value is not returned. The result is rounded towards zero; thus if a is negative, the remainder will be zero or negative. For division by powers of 2, use BN_rshift(3).

BN_mod() corresponds to BN_div() with dv set to

.

BN_nnmod() reduces a modulo m and places the non-negative remainder in r.

BN_mod_add() adds a to b modulo m and places the non-negative result in r.

BN_mod_sub() subtracts b from a modulo m and places the non-negative result in r.

BN_mod_mul() multiplies a by b and finds the non-negative remainder respective to modulus m ("r=(a*b) mod m"). r may be the same

as a or b. For more efficient algorithms for repeated computations using the same modulus, see BN_mod_mul_montgomery(3) and BN_mod_mul_reciprocal(3).

BN_mod_sqr() takes the square of a modulo m and places the result in r.

BN_exp() raises a to the p-th 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-th 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. r may be the same

as a or b.

For all functions, ctx is a previously allocated

used for temporary variables; see BN_CTX_new(3).

Unless noted otherwise, the result

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 ERR_get_error(3).

SEE ALSO

bn(3), ERR_get_error(3), BN_CTX_new(3), BN_add_word(3), BN_set_bit(3)

HISTORY

BN_add(), BN_sub(), BN_sqr(), BN_div(), 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. BN_exp() appeared in SSLeay 0.9.0. BN_nnmod(), BN_mod_add(), BN_mod_sub(), and BN_mod_sqr() were added in OpenSSL 0.9.7.