The index of that column is the plaintext letter. Onewrites the keyword repeatedly above the message: Keyword: RELAT IONSR ELATI ONSRE LATIO NSRELCiphertext: KSMEH ZBBLK SMEMP OGAJX SEJCS FLZSY Plaintext: tobeo rnott obeth atist heque stionThis time one uses the keyword letter to pick a row of the table andthen traces across the row to get the column containing the ciphertextletter. Keyword: RELAT IONSR ELATI ONSRE LATIO NSREL Plaintext: tobeo rnott obeth atist heque stionCiphertext: KSMEH ZBBLK SMEMP OGAJX SEJCS FLZSYDecipherment of an encrypted message is equally straightforward. To derivethe ciphertext using the tableau, for each letter in the plaintext,one finds the intersection of the row given by the correspondingkeyword letter and the column given by the plaintext letter itself topick out the ciphertext letter.
We begin by writing the keyword, repeatedas many times as necessary, above the plaintext message. For example, suppose we wish to encipher theplaintext message: to be or not to be that is the question The Vigenere cipher uses this table together with a keyword toencipher a message. The first row is a shift of 0 the second is a shift of 1 and the last is a shift of 25. The Vigenere TableauThe Vigenere Cipher, proposed by Blaise de Vigenere from the court of Henry IIIof France in the sixteenth century, is a polyalphabetic substitutionbased on the following tableau: 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 ZA 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 ZB 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 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 BD 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 UW 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 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 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 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 Note that each row of the table corresponds to a Caesar Cipher. Instead of there being a one-to-one relationship betweeneach letter and its substitute, there is a one-to-many relationshipbetween each letter and its substitutes. A polyalphabetic substitutioncipher involves the use of two or more cipheralphabets. One of the most common approaches is to suppressthe normal frequency data by using more than one alphabet to encryptthe message. Therefore, to make ciphers more secure, cryptographers have long beeninterested in developing enciphering techniques that are immune tofrequency analysis. Given a sufficientlylarge ciphertext, it can easily be broken by mapping the frequency ofits letters to the know frequencies of, say, English text. One of the main problems with simplesubstitution ciphers is that they are so vulnerable to frequency analysis. Vigenere Cipher The Vigenere Cipher Author: R.
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