Cryptography: It's Not Just For Electronic Mail Anymore
J. D. Tygar, Bennet Yee · 1993
This report extends cryptographic techniques to the protection of the application of stamps for mail. We show how to provide electronic stamps (using off-the-shelf bar code technology to represent a cryptographic message) to use in a fully integrated franking system that provides protection against: (1) Tampering with postage meter to given the user additional credit; (2) Forged or copied electronic stamps; (3) Unauthorized use of a postage meter; and (4) Stolen postage meters. The report relates the question of electron stamps to broader issues in electronic currency and secure coprocessors.