# bn_mod_inverse(3ssl) [minix man page]

```BN_mod_inverse(3SSL)						      OpenSSL						      BN_mod_inverse(3SSL)

NAME
BN_mod_inverse - compute inverse modulo n

SYNOPSIS
#include <openssl/bn.h>

BIGNUM *BN_mod_inverse(BIGNUM *r, BIGNUM *a, const BIGNUM *n,
BN_CTX *ctx);

DESCRIPTION
BN_mod_inverse() computes the inverse of a modulo n places the result in r ("(a*r)%n==1"). If r is NULL, a new BIGNUM is created.

ctx is a previously allocated BN_CTX used for temporary variables. r may be the same BIGNUM as a or n.

RETURN VALUES
BN_mod_inverse() returns the BIGNUM containing the inverse, and NULL on error. The error codes can be obtained by ERR_get_error(3).

HISTORY
BN_mod_inverse() is available in all versions of SSLeay and OpenSSL.

1.0.1e								    2013-02-11						      BN_mod_inverse(3SSL)```

## Check Out this Related Man Page

```BN_add(3SSL)							      OpenSSL							      BN_add(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 BIGNUM 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 BIGNUM 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 BIGNUM.  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 NULL, 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 NULL.

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 BIGNUM 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 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 ERR_get_error(3).