Polyalphabetic Ciphers History Alberti

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

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

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)

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

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)

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.

Practice of Cryptography

• Polyalphabetic not used until 19th 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

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.

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