For a very simple exercise in cryptanalysis, let us see how one would go about breaking a "Caesar cipher" (an encryption technique apparently in use during ancient Rome -- hence the name). The idea is to create a table of source letters and target letters, each letter occurring exactly once in each column. The encryption program (Caesar's royal scribe) takes the plain text message letter by letter, looks up each letter in the source column, and transcribes the corresponding target letter onto the cipher text tablet.