This was prompted by Doug McIlroy's "Dual Cryptograms" (Word Ways, August 1997). A dual cryptogram is two texts, each of which results from enciphering the other using a substitution cipher. This means that occurrences of the same letter in the first text are replaced by occurrences of the same letter in the second; different letters in the first are replaced by different letters in the second. No letter may stay as itself. Spaces are preserved; punctuation may be added or removed at will, and the distinction between lower and upper case is ignored. Although Doug treated hyphens like spaces, I treat them like other punctuation, so that word-breaks all correspond to word-breaks.
"Two Dual Cryptograms,"
Word Ways: Vol. 34
, Article 14.
Available at: http://digitalcommons.butler.edu/wordways/vol34/iss3/14