Type the encoded puzzle into the "Cipher Text" box. If you know any letter mappings (e.g., "A=R"), type those into the "Clues" box. Finally, click "Solve".
There are several different solving options available from the popup menu near the "Solve" button:
In most cases, Decrypto will completely solve the puzzle in a fraction of a second. Hard puzzles, in which there are several non-dictionary words, or that are very short (under 50 characters), or whose answers are statistically unlikely, can take somewhat longer. For dictionary attacks, a few minutes can occasionally be needed; the genetic methods can require 10 minutes or more. It's worth trying different methods, however: they have different strengths and weaknesses.
On especially hard puzzles, you can guide Decrypto towards the correct solution. Even if Decrypto does not find a perfect answer, the guesses it produces can often give a human insight into the correct solution. Perhaps a word or two "look right". Use this observation to add new clues to the puzzle and run Decrypto again.
For most cryptograms (in which word boundaries are known), the dictionary attack options are generally the most successful. If the default method does not work, switching to "Dictionary Attack++" or "Genetic, trust spaces" will generally yield a usable answer.
Often, Decrypto can solve puzzles without any clues. On hard puzzles, though, clues can make an important difference. There are several ways of specifying clues.
| Q=R W=A B=C | Tells Decrypto that Q must equal R, W must equal A, and B must equal C. |
| QWB=RAC | Same as above. |
| Q!=D | Q is not equal to D. |
| Q!=DEF | Q is neither D, E, nor F. |
| QWB!=DEF | Q is not D, W is not E, B is not F. |
If there are words which should not be considered while solving (because they might not be in the dictionary), include a carat ("^") in front of the word in the ciphertext box. This is particularly useful when you can guess which words might be proper nouns (such as a quote).
If you know that the puzzle contains no identity-mappings (i.e., no letters map to themselves), you could specify the clue "ABCDEFGHIJKLMNOPQRSTUVWXYZ!=ABCDEFGHIJKLMNOPQRSTUVWXYZ", or more easily, deselect the "allow identity mappings when solving" option from the Advanced menu.
You can pick a new dictionary by using the Dictionary menu. Note that the selected dictionary only significantly affects the dictionary based methods. (The genetic algorithms do not make significant use of the dictionary).
The standard English dictionary is good for a wide variety of puzzles, however there are occasions where a different dictionary will perform better. On very short puzzles that (probably) contain only common words, smaller dictionaries will reduce the number of "false positives" while simultaneously decreasing the time required to search. On puzzles containing uncommon words (including names and acronyms), larger dictionaries are generally better.
Type the unencoded puzzle into the "Cipher Text" box. Enter any clues that you would to provide. (Since you're providing the undeciphered puzzle in the "Cipher Text" box, you should enter clues like "R=R", or "RACER=RACER". After encoding, the clues box will updated accordingly.)
Click scramble. You can hit scramble as many times as you like until you get a permutation that you like. By default, the encoding process will prevent a letter from ever mapping to itself. This can be changed by deselecting the "allow identity mappings while encoding" option from the Advanced menu.
From the Dictionary menu, select "Dictionary Editor...". This will allow you to merge dictionary files and word lists in order to create new dictionaries. While you can add words using the editor, using an external editor (like Notepad) is generally easier. You can then import the whole file in one operation. Plus, if you save your additions to a separate file, you can send them to me to be included in a future release of Decrypto.
Notes: A word list is just a newline-terminated list of words, which you can create in any editor. Also, do not change the "Language Class" setting unless you know what you're doing!
If you find any words that are missing from the standard dictionary, please email me them (eolson@mit.edu) and I will add those words to the next version.
Decrypto 8.5 supports puzzles in multiple languages, at least in theory. However, I have only built the appropriate data files for English. Supporting new languages requires a very large corpus of sample text, a dictionary file, and a small amount of programming know-how (which I could help you with). Please contact me if you are interested in helping.
Important: Creating good dictionaries is hard work. Too few words and the solver won't find good solutions. Too many words (i.e., if you just use a spell-checking dictionary filled with acronyms, colloquialisms, and other nonsense), and you'll get gibberish. As a general strategy, be sparing when adding words, and definitely do not indiscriminately merge the dictionary with another large word list.
The advanced menu includes several options that may be of interest to advanced users. These options are all set to reasonable values, however, so most users won't need to modify any settings.
Identity mappings, in which a ciphertext letter maps to the same plaintext letter (e.g., "R=R"), can be disabled both when encoding and decoding puzzles. When decoding puzzles, disabling identity mappings can provide a noticeable increase in speed-- however, the algorithm obviously will not work if the solution requires an identity mapping!
Fewer Tildes in Solutions. When Decrypto's dictionary attacks reach a "dead-end" when solving (when a ciphertext word cannot be mapped to a dictionary word while respecting the current set of mappings), there are often several mappings have not yet been determined. These unknown letters are displayed as tildes ('~'). As of version 8.5, Decrypto includes an algorithm that attempts to guess these last few mappings based purely on statistics. When this option is selected, this algorithm will be used when the number of unknown mappings is relatively small.
Only allow dictionary words. When using the dictionary-based attacks, Decrypto usually employs a number of techniques for dealing with words that do not appear in the dictionary, increasing the number of puzzles that Decrypto can solve. This option disables this behavior: only solutions containing only dictionary words will be reported.
Maximum Solutions. By default, Decrypto will track the 500 best-scoring solutions (based on their 4-gram probabilities). The number of retained solutions can be modified using this menu.
Testing Options. These options are where various debugging options are hidden. They are not intended for users; they may or may not do anything.
Cipher text: "PG XOYHLM XOYLY PZ GH TPUUYLYGRY EYXBYYG XOYHLM WGT JLWRXPRY. PG JLWRXPRY, XOYLY PZ." - MHIP EYLLW
Clues: X=T M=Y
The source code for this software is available from the Decrypto homepage:
http://www.blisstonia.com/software/Decrypto
It is distributed under the terms of the GPL version 2. I welcome patches and improvements!
Pete Wiedman did a great deal of work in preparing the excellent dictionaries which come with Decrypto 8.x, not to mention lots of invaluable testing. Also, thanks to John Gidusko for his part in preparing the dictionaries. Thanks!
Ken Cline made the helpful observation that--occasionally--it is more productive to search for a single letter at a time than to search for a whole word. This has made a significant performance improvement on a class of difficult puzzles.
Dictionary attack methods are the classic method of solving cryptograms, but the method used by Decrypto 8.x contains several critical refinements. These refinements are described in a paper published in the journal Cryptologia in 2007. You can download the paper here: http://edwinolson.org/papers/cryptologia2007/eolson_decrypto2007.pdf
The genetic algorithm idea is similar to work by [Spillman, et al 1993]. I have attempted to make it smarter in various ways, but the performance of this genetic algorithm--like other genetic approaches-- tends to be spotty. I have modified the searching in an attempt to make it less likely to get stuck in local minima. However, more research is required here.
This program has taken a lot of time to develop. If you would like to contribute a pizza+coke for one more night of hacking, please consider using PayPal (www.paypal.com). I am registered on PayPal as "eolson@mit.edu". If you do not use paypal, please contact me for a mailing address!
Thanks to those who have already contributed!