It is possible to pass an ENGINE name to certain cipher and digest related functions. The file provider_util.c is supposed to handle creating and managing ENGINE references as required.

However, ossl_prov_cipher_reset and ossl_prov_digest_reset will leak any engine references associated with the cipher/digest leading to memory leaks. Additionally ossl_prov_cipher_copy and ossl_prov_digest_copy fail to copy engine references correctly which would lead to double frees (if it wasn't for the fact that the "reset" functions leaked them anyway).