Rotate 13. It is its own inverse.
Revese the alphabet. It is its own inverse.
verifying solutions when spaces are omitted. can rate fitness using corpus information on popularity
Shift along in alphabet by \(c\).
page on affine cipher too. like caesar but rather than +c, mx+c
For Caesar, only 26 possible keys, can just brute force.
For Affine, can also brute force.
(key plus algorithm encrpyts and decrypts)
(need to identify algorithm and needs to identify key)
finding substitution cyphers
Search space is larger, \(26!=4*10^26\). need alternative to brute force.
Letter popularity. Compare against popularity for corpus. Monogram (ie letters); ngrams(ie n letter in a row frequency); common words.
Single letter words are I or A. More generally. corpus smaller for fewer letters
Can test substitution cypher by matching each word against a corpus
( (eg sdrgdr is code for “meet at x on y”)
Eg use Bible.