1. Polyalphabetic Ciphers History

2. Alberti Rennaisance Architect –First fountains of Trevi, Rome –Churches 1467 essay on cryptology –Frequency analysis –Cipher disk for polyalphabetic cipher Scrambled alphabet Changed key letter only after 3 or 4 words

3. Alberti’s cipher disk F E D C B A T R A P E M Z J

4. Johanne Trithemius German Monk Known for magic Wrote Polygraphia in 1518 –Introduced tableaux of shifted alphabets –But just went from one alphabet to the next First letter with first alphabet, second with second, etc.

5. Tritemius Tableaux a b c d e f g h i j k l m n o p q r s t u v w x y z --------------------------------------------------- A B C D E F G H I J K L M N O P Q R S T U V W X Y Z B C D E F G H I J K L M N O P Q R S T U V W X Y Z A C D E F G H I J K L M N O P Q R S T U V W X Y Z A B D E F G H I J K L M N O P Q R S T U V W X Y Z A B C E F G H I J K L M N O P Q R S T U V W X Y Z A B C D F G H I J K L M N O P Q R S T U V W X Y Z A B C D E G H I J K L M N O P Q R S T U V W X Y Z A B C D E F H I J K L M N O P Q R S T U V W X Y Z A B C D E F G I J K L M N O P Q R S T U V W X Y Z A B C D E F G H J K L M N O P Q R S T U V W X Y Z A B C D E F G H I K L M N O P Q R S T U V W X Y Z A B C D E F G H I J L M N O P Q R S T U V W X Y Z A B C D E F G H I J K M N O P Q R S T U V W X Y Z A B C D E F G H I J K L N O P Q R S T U V W X Y Z A B C D E F G H I J K L M O P Q R S T U V W X Y Z A B C D E F G H I J K L M N P Q R S T U V W X Y Z A B C D E F G H I J K L M N O Q R S T U V W X Y Z A B C D E F G H I J K L M N O P R S T U V W X Y Z A B C D E F G H I J K L M N O P Q S T U V W X Y Z A B C D E F G H I J K L M N O P Q R T U V W X Y Z A B C D E F G H I J K L M N O P Q R S U V W X Y Z A B C D E F G H I J K L M N O P Q R S T V W X Y Z A B C D E F G H I J K L M N O P Q R S T U W X Y Z A B C D E F G H I J K L M N O P Q R S T U V X Y Z A B C D E F G H I J K L M N O P Q R S T U V W Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Z A B C D E F G H I J K L M N O P Q R S T U V W X Y

6. Giovan Battista Belaso Otherwise unknown Small booklet in 1553 Used Trithemius’ tableaux of shifted alphabets Added the idea of a key word or phrase –The longer the better

7. Giovanni Battista Porta Wrote several books –Scientific subject –Magic Book on cryptology: De Furtivis Literarum –1563 –Included classification of methods –Cryptanalysis How to solve monoalphabetic with no word breaks Likely word method –Digram cipher (using non-letter symbols)

8. Giovanni Battista Porta Polyalphabetic cipher –Combined elements of Alberti – scrambled alphabet Trithemius - letter-by-letter change of alphabet Belaso – key word/phrase –Scrambled alphabet could be from Alberti style disk or from table

9. Blaise de Vigenere From age of 24 served the Duke of Nevers (France) in Court and as Diplomat –2 years in Rome as diplomat introduced him to cryptology Quit the court in 1570 (age 47) and wrote on many subjects Wrote Traicte de Chiffres in 1585 –Collected much previous work (with credit)

10. Vigenere Polyalphabetic cipher –Tableaux like Trithemius –But scrambled alphabet on borders Makes it like Alberti’s disk –Discussed several key methods Words, phrase, poetry Date of dispatch Ordered, like Trithemius –New contribution! –Autokey Text itself is the key! Key letter or word to start, then each letter in message is key for the next.

11. Practice of Cryptography Polyalphabetic not used until 19 th century Era of “Black Chambers” –Government agencies for cryptanalysis –French, Italian, German, Austrian –Encryption typically used ciphers and nomenclators (combined code and cipher) Introduction of telegraph (1840s) led to use of better methods, polyalphabetic

12. Vigenere Ironically has name attached to easy version of polyalphabetic, as done by Porta, not his better autokey system. We will look at this method and how to break it.