We present a method based on abstract interpretation for verifying secrecy properties of cryptographic protocols. Our method allows to verify secrecy properties in a general model allowing an unbounded number of sessions, an unbounded number of principals and an unbounded size of messages. As abstract domain we use sets of so-called pattern terms, that is, terms with an interpreted constructor, Sup , where a term Sup (t) is meant for the set of terms that contain t as sub-term.We implemented a prototype and were able to verify well-known protocols such as for instance Needham-Schroeder-Lowe (0.02 sec), Yahalom (12.67 sec), Otway-Rees (0.02 sec), Skeme (0.06 sec) and Kao-Chow (0.07 sec).