BN_mod_inverse

BN_mod_inverse ? compute inverse modulo n

 #include <openssl/bn.h>

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

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.

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

bn(3), err(3), BN_add(3)

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