This was one of the most secure hand ciphers used in the Second World War. It was used by both the Allies and the Axis, and served both well. Its main weakness was that if the attacker intercepted two ...

However, Agent Madeleine numbered the duplicate A's and L's from right to left instead of from left to right, so it would be the equivalent of replacing the keys with MCHBTUNDILA and CUMLBTJNDIKA, ...

The envelope arrived at the San Francisco Chronicle in November 1969 without a return address, its directive to the recipient, in handwriting distinctively slanted and words unevenly spaced, to ...

I hope you enjoyed Ed’s guest posts on NP-complete problems on TV the last couple of Mondays. It’s always great to hear from others on math that they are thinking about. This week it’s me again, and ...

Introduction to ciphers and substitution. Alice and Bob and Carl and Julius: terminology and Caesar Cipher ; The key to the matter: generalizing the Caesar Cipher ; Multiplicative ciphers ; Affine ...