An improved system for protecting cryptographic processing and memory for postal franking machines. Appropriate cryptographic processing and memory resources are contained in a Postal Security Device (PSD), which defines a cryptographic and physical boundary. Cryptographic processing occurs in the PSD, which provides security to these resources, thereby minimizing a successful fraudulent attack on the system. Speed of the cryptographic processing is also increased. The PSD may be in the form of an Applications Specific Integrated Circuit (ASIC) or Personal Computer Memory Card International Association (PCMCIA) Card.