LIGN 17 Study Guide - Final Guide: Substitution Cipher, Transposition Cipher, Book Cipher
20 Mar 2017
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Document Summary
Secret communication by hiding the message"s existence. Symbols in the plain text keep their identities but switch positions. If there is not the same amount of letters in each row, then the earlier rows will have more than the later rows. Symbols keep their positions but change their identity. Kerchoff"s principle the security of a cryptosystem depends only on keeping secret the key. You have to assume that everyone knows the algorithm. Vigenere: pick a key, pick the cipher alphabets that start with that letter of the key and finding the letter of the plain text on top. One time pad cipher: have a pad with randomly generated key phrase, given the cipher text, any plain text of the same length is possible this method is mathematically unbreakable. Book cipher: do a substitution and the key phrase is a book or document, you can number every word or every letter, most similar to msc with homophones.
