In many cryptographic protocols, the actions performed by principals are iterative processes. However, in contrast to other classes of protocols, only very little is known about deciding the security of such protocols. To analyze decidability for these protocols, we propose a protocol model in which the actions of principals are described by tree transducers with regular look-ahead. The main result is that security in this model is decidable and EXPTIME-hard in presence of the standard Dolev-Yao intruder
