# Computer cipher solving – Lesson 6: interactive solvers

I’ve had a fun three days at the ACA convention in Dallas but I’m back and ready to finish up this topic. There is way too much involved in computer solving to cover it all in my blog, so this is going to be my last post on the subject for now. I just hope that I’ve given you enough inspiration and maybe some clear understanding of how you can solve ciphers with computers.

Perhaps the most valuable and easiest computer solving program you can write is an interactive solver that mimics what you would do to solve it on paper. For example, with a simple cryptogram, a good interactive solver will allow you to input the ciphertext, display it in a handy way and have a way to input a letter you want to substitute for another, such as typing the letters in text fields or by clicking a mouse on an alphabet, etc. When you tell it that G=A it will go through the program and display above (or below if you prefer) an A over every G. It will also display a key alphabet equivalence. The advantage of using a computer program is that it makes all the substitutions or transpositions immediately and error-free . It should allow you to delete or undo some action you’ve tried. Such a program avoids all the transcription errors and messy erasures and can provide some useful statistics such as the frequency count. Even if you have an automatic solver (like a hillclimber) for a cipher type, you should probably also have an interactive solver since the automatic ones aren’t always so automatic.

I include in this class programs that perform a single useful task. A good example would be a crib placer. Many puzzlers provide a crib (short plaintext segment) along with the cipher, but usually the location is not known. A crib placer can tell you all the places it can fit. Another example would be a program that computes useful statistics such as letter frequency count, index of coincidence, Normor score, and so forth.

Many serious programmers are used to working in a command-line environment. That’s fine if that’s what you like, but I really like graphic user interfaces (GUIs). A decent GUI will allow you to see plaintext in one color and ciphertext in another. It will allow a large or small font. It provides nicely labeled input and output boxes. It will allow you to interrupt or pause execution when things look promising. It will display everything in nice neat rows or columns. It can highlight things of interest such as a possible placement for a crib, or a count of the number of trial decrypts it has done. As I mentioned earlier, I’m not much of a programmer. I’ve never worked as one and I don’t know the languages that are now popular, but I know that I solve ciphers better when I can see things displayed in the way I want them displayed. Cut, paste, click the button, and watch it go. I’ve learned enough to do that.

So how do you write one? For each cipher it will be different, but most programmers will not have trouble figuring out how to do that. For non-programmers, though, you can get much of this functionality with programs you already have available such as spreadsheets, word processors, and, of course, an Internet full of interactive solvers.

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