Between 1945 and 1954, the staff of Spanish prisons used an encryption method based on a cipher slide and a table. Can my readers help to understand how this system worked?

A US magazine has published a letter containing a hidden message written by a prison inmate. The message is given, but the method used has not been published. Can a reader solve this mystery?

Craig Bauer, mathematics professor and crypto history expert, lets his students solve old ciphertexts as homework. Here are three especially interesting cryptograms Craig’s students have to break.