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• Uncommon words are a common plan. The less recognizable a pattern, the tougher it is.
• Common patterns; Book, tool and moon would be hard to decode. Adding reel, rook and room would be a challenge, too.
• Isomorphs – words that never use a letter twice – can be as hard when, for example, all the words are also six letters long.
• Skewed letter counts. Everyone knows “E” is the most common letter in normal English writing. Cryptograms are not “normal English writing,” though. You can expect the uncommon letters to be more frequent.
• Composers will avoid contractions and the pronoun “I,” as well as the article “a.” These all leave one or two letters that will allow you to break into the puzzle.

Almost all the things that make a Crypt challenging also make it interesting.

Sometimes, there is a second message in the decoding. ROT13 is one example of a slightly interesting version of this, but you can't claim to have come up with that. Sometimes, the crypt composer will hide something in the solution alphabets so that, if you write the alphabets out, you might see something like:

  ABCDEFGHIJKLMNOPQRSTUVWXYZ  
  NIGHTOWLABCDEFJKMPQRSUVXYZ

Note that, if XYZ were used in the crypt, it would not be legal since they “stand for themselves.” What makes this solution interesting is that the composer has used a specific word to encrypt the solution (Nightowl). This is reported to have been used to help prevent decoding messages; one messenger would carry the encoded message on paper, another would deliver the keyword by another route; without the keyword, decoding the message would be more difficult (but nowhere near impossible).

• The official site of the American Cryptogram Association or ACA; their old site
• We also offer The Penrose Cryptogram Tool to help you solve cryptograms.
• Brutus, our cryptogram solver, is only available to Members

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