Polyalphabetic Ciphers

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Presentation transcript:

Polyalphabetic Ciphers Vigenere

Main Idea Use multiple monoalphabetic ciphers Change alphabet every letter Variations possible, but simple version seems to have been commonly used (even though it can be broken)

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

Vigenere Scheme Keyword (or phrase) used to indicate which alphabet to use for encoding (by first letter) Keyword repeated over plaintext. The key-letter over each plaintext letter determines the alphabet used to encipher that letter Example: use cryptology as keyword

Vigenere Example CRYPTOLOGYCRYPTOLOGY computerscienceisthe studyofdatastructure sandalgorithmsandthe CRYPTOLOGYCRYPTOLOGYCRYPTOLO irimplementationsoncomputers

Vigenere Example CRYPTOLOGYCRYPTOLOGY computerscienceisthe EFKENHPFYAKVLRXWDHNC studyofdatastructure UKSSRCQRGRCJRGNQEIXC sandalgorithmsandthe URLSTZRCXGVYKHTBOHNC CRYPTOLOGYCRYPTOLOGYCRYPTOLO irimplementationsoncomputers KIGBIZPAKLVRRXHBDCTAQDNJMSCG