CMPUT175 Chapter Notes - Chapter 8: Substitution Cipher, English Alphabet, Letter Frequency
1 Nov 2017
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8. 3: cracking the rail fence: the rail fence cipher is used by deciding on the number of rails" and then filling in the rails top to bottom and left to right with the message characters. Once the rails are filled, a new string is created for each one, and the strings are concatenated together: using the brute force approach can result in many lines of gibberish. ade = fade or wade or 3ade or fader: [ ]" allows us to define a set of characters, any one of which may match. [abc] will match a, b, or c, but not d. Be[l-o]t" matches belt, bemt, bent, or beot: [^ ] allows us to define a set of characters, of which any other character can match. [^abc] will match any character other than a, b, or c. Be[^0-9]t" will match belt and be#t, but not be4t: the +" character allows us to match one or more repetitions of the character.
