A postal system includes a local computer (110, 300) having a user interface (316, 318) and an associated storage unit (322) for storing a secure data file that contains postal (e.g., accounting) data. A secure processing unit (140, 340, 400) interfaces with the local computer (110, 300) and performs the secure processing normally associated with a secure postal environment. The secure processing unit (140, 340, 400) can be designed to receive power from the computer to which it couples, and generally does not require special interconnect. By using the secure processing unit (140, 340, 400) to perform the secure processing and the local computer (110, 300) to perform other postal functions (e.g., user interface), complexity is reduced which translates to faster speed of operation and a more economical hardware design.