We present an NP decision procedure for insecurity in the case of finite sessions and non-atomic encryption keys (and no fixed bound on the size of messages). We also explain that in order to build an attack with a fixed number of sessions the intruder needs only to forge messages of linear size, provided that they are represented as dags. This is joint work with Mathieu Turuani and is based on our paper presented in June 2001 at 14th CSFW. for more information: http://www.loria.fr/equipes/protheo/SOFTWARES/CASROL/