The complexity exhibited by pervasive systems is constantly increasing. Customer electronics devices provide day to day a larger amount of functionalities. A common approach for guaranteeing high performance is to include specialized coprocessor units. However, these systems lack flexibility, since one must define, in advance, the coprocessor functionality. A solution to this problem is to use run-time reconfigurable coprocessors, exploiting the advantages of hardware while keeping a flexible platform. In this paper, we describe a self-reconfigurable pervasive platform containing a dynamically reconfigurable cryptographic coprocessor. As case-study, we consider three ciphering algorithms and we compare the performance of the coprocessor against a full-software implementation. The number of ciphering algorithms can be infinitely extended using a remote server.