Cryptology ROT13

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Description

ROT13 is a shift cipher over the alphabet {A, ..., Z} that replaces each letter by the one 13 positions ahead in the alphabet. As tool take the table

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

As encryption function this is trivial—in view of the previous section we even might consider ROT13 simply as a code. Its purpose is hiding some texts, say of offensive content, from immediate recognition. The reader can figure them out only by a conscious act.

Since 13 + 13 = 26, double encryption restores the plaintext. That is, encryption = decryption as functions.

Example

          DU BIST DOOF (plaintext)  
          QH OVFG QBBS (ciphertext)

Exercise

    JREQV RFYRF RAXNA AUNGE BGRVA FQERV IREFG NAQRA