BN_mod_inverse - compute inverse modulo n

       Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use this file except in compliance
       with the License.  You can obtain a copy in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.

3.5.0                                              2025-06-04                               BN_MOD_INVERSE(3SSL)

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.

       BN_mod_inverse - compute inverse modulo n

       It is an error to use the same BIGNUM as n.

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

ERR_get_error(3), BN_add(3)

        #include <openssl/bn.h>

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