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BN_MOD_INVERSE(3) Library Functions Manual BN_MOD_INVERSE(3)

BN_mod_inversecompute inverse modulo m

#include <openssl/bn.h>

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

() computes the inverse of a modulo m and places the result in r, so that r satisfies a * r == 1 (mod m). If r is NULL, a new BIGNUM is allocated.

If the flag BN_FLG_CONSTTIME is set on a or m, it operates in constant time.

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

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

BN_add(3), BN_new(3), BN_set_flags(3)

BN_mod_inverse() first appeared in SSLeay 0.5.1 and has been available since OpenBSD 2.4.

The r argument was added in SSLeay 0.9.1 and OpenBSD 2.6.

October 21, 2023 OpenBSD-current