Sorry for distracting people with my T-shirt suggestion, but the more I think about it, the more I like "celebrating 4000 years..." -- possibly on the back. On the front, I'd have 4 boxes (or regions set apart): LEB KAMAI y_i = x_i + k_{(i mod m)} y_i = x_i (+) k_i y = x^e mod N -------------------------------------------------- 1. LEB KAMAI, in Hebrew characters from the Bible -- cf., Kahn's "The Codebreakers", pp. 77-78 -- atbash cipher, stronger than Caesar's and predating him by more than a month :-) 2. polyalphabetic substitution -- stronger than nomenclators (based on when attacks were known to exist) but ignored by gov't users for 100s of years 3. Vernam's tape -- theoretically unbreakable -- in the hands of citizens from about 1920 {the (+) is a circled "+" -- meaning XOR} 4. RSA -- 1978 -------------------------------------------------- It might be interesting to date the four boxes. Anyone have a date for the LEB KAMAI? - Carl