Strategy to crack a presumed substitution cipher

Question

The ciphertext given is:

ejitp spawa qleji taiul rtwll rflrl laoat wsqqj atgac kthls iraoa twlpl qjatw jufrh lhuts qataq itats aittk stqfj cae

I've done frequency analysis on the text. That yielded the following results:

A(15), B(0), C(2), D(0), E(3), F(3),  G(1), H(3), I(6), J(6), K(2), L(11), M(0),
N(0),  O(2), P(3), Q(7), R(5), S(6), T(15), U(3), V(0), W(5), X(0), Y(0),  Z(0)

There are 120 characters total. The format of the ciphertext does not match the format of the quote from which it was created.

The most common digrams (in order of most frequent to least, max 6, min 2):

at, it, tw, lr ,ta, ej, ai, ao, aq, ll, ts, wl, ji, hl, ja, sq, oa, qj

The most common trigrams in the same order (max 3, min 2):

atw, ita, jat, jit ,eji, twl, oat, aoa, qja

I've tried substituting character a few at a time to see if I could start to make out some words, but every time I have ended up with letters next to each other that don't make any sense.

I don't need the exact answer, but if someone could help point me in the right direction I would appreciate it. The answer would be great too, but I'd really like to understand the process here.

Answer 1

There are different approaches to crack a substitution cipher.

A human would use a different strategy than a computer. But as the word boundaries are not preserved it will be rather challenging for a human solving this cipher.

The quipqiuq tool mentioned by John is using word lists, but there are other methods as well.

Resources:

• http://reflectionsonsecurity.files.wordpress.com/2011/03/fast-reliable-cryptanalysis-of-simple-substitution-ciphers.pdf
  This paper proposes to use the genetic algorithm.
• http://practicalcryptography.com/cryptanalysis/stochastic-searching/cryptanalysis-simple-substitution-cipher/
  Describes how to crack a substitution cipher using the hill-climbing algorithm.
• http://www.cryptoden.com/programs/Ari_Pat_WW.html
  This solver is using the hill climbing approach. The good thing is that you can study the Javascript code. I think this tool expects the cipher text in upper cases.
• http://www.guballa.de/pages/geocaching/substitution-solver.php
  This solver uses the hill climbing approach as well.

Note: If feeding your cipher text one of the online tools above you will notice that the word "sherlock" was used to generate the cipher alphabet.

Answer 2

You can solve it at http://www.quipqiup.com/index.php in about 5 seconds.

contrariwise continued tweedle dee if it was so it might be and if it were so it would be but as it isnt it aint thats logic

It's an excerpt from Through the Looking-Glass by Lewis Carroll

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