BN_mod_inverse(3)

     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).

     SEE ALSO
          bn(3), ERR_get_error(3), BN_add(3)

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