Briefly, the CSA breaks up the input ciphertext into a list of
words, and recursively tries to fit as much of the list as
possible to the words in a fairly long list of English words,
longest word first. It tries to find the trial solution with the
maximum number of words fitted with the same key, among all the
recursive tree walks made. The CSA is very strongly dependent on
the input having the word boundaries and lengths correct, so
that, for example, a ciphergram redivided into five letter
groups will not work. It is a little less dependent on having no
wrong letters in the text, but it thinks words of three letters
or less are all exact and in its word list, so a mistake in a
short word will almost surely cause it to fail. Two newspaper
cryptoquotes in 1997 had the word "oh" in them, and because that
word was not in the known word list, they failed, so now the
list contains "oh". The "Los" of Los Angeles tripped the CSA
once. Nearly all cases that take a long time are caused by input
having a letter left