Porta Cipher: Table Use and Crib-Based Cryptanalysis

Your alarm goes off and, after hitting “snooze” once or twice, you pry yourself out of bed. You make a cup of coffee to help you get going, and then you shower, get dressed, eat breakfast, and check your phone for messages. On your way to school, you stop to fill your car’s gas tank, almost making you late for the first day of chemistry class. As you find a seat in the classroom, you read the question projected on the screen: “Welcome to class! Why should we study chemistry”

Figures (7)

Giambattista della Porta's music cipher from De Furtivis Literarum Notis (1602).

Music Cipher attributed to Michael Haydn (1808)

Motivic music cipher by Johann Bücking (1804)

Polybius square music cipher designed by Friedrich von Öttingen-Wallerstein (ca. 1600)

Music Cipher Wheel from anonymous 18th-century manuscript, Port-Lesney, France

Key Points

After the plaintext is enciphered, additional pre-composed measures are appended to the beginning and end to provide a suitable musical framing.
In the case of the former, the compound symbols are to make frequency analysis more difficult; in the latter, the goal is to make the output more musical.

Terms

Tap a term for a plain-language explanation.

Sources & licensing(4)

OpenStax — openstax.org/books/chemistry-2e/pages/1-introduction (Creative Commons Attribution 4.0)
Wikipedia contributors — en.wikipedia.org/wiki/Music_cipher (Creative Commons Attribution-ShareAlike 4.0)
Wikipedia contributors — en.wikipedia.org/wiki/Known-plaintext_attack (Creative Commons Attribution-ShareAlike 4.0)
Wikipedia contributors — en.wikipedia.org/wiki/Polyalphabetic_cipher (Creative Commons Attribution-ShareAlike 4.0)