The “gform_use_mcrypt” filter in Gravity Forms indicates whether the function “mcrypt_encrypt” should be used for encryption. This filter was called in Gravity Forms’ encrypt/decrypt functions in the GFCommon class.

These functions have been deprecated as of Gravity Forms version 2.3, meaning the filter will no longer be used for encryption.

The new functions used for encryption are “openssl_encrypt” and “openssl_decrypt” which do NOT use mcrypt.