Cracking Codes: Part III

It’s been a little while since our last cracking codes post, but here’s a classic for you to sink your teeth into this Sunday – the Telephone Keypad Cipher.

A standard touch-tone telephone keypad can be used to create a number cipher that is more difficult to break than a keyword system.

Using the telephone keypad at the bottom of this page, the criminal (or spy) can substitute numbers with the letters corresponding to the telephone button. The numbers 0 and 1 have no corresponding letters, which can throw both those encrypting and decrypting off. Sometimes the letters Q and Z are substituted for the numbers 0 and 1 because older telephone keypads omitted the letters Q and Z. The telephone number (202) 324-5678, for example, could be enciphered any of the following ways:

BBQ DAG KMRV
CQA FBI JNPX
AQB ECH LOST

Telephone keypad systems can use all 26 letters in the alphabet and thus are easily confused with enciphered words. Any cryptanalyst worth his/her salt will find out through further analysis of the letter combinations that there is no possibility that the cipher text conceals words. The downside (or the upside, depending which side you happen to be on) is that once identified, telephone keypad ciphers are easily decrypted.