I have found an encrypted letter/postcard/diary/telegram/note somewhere, will you crack it for me?

Please send it to Klaus (klaus-codebreaking@gmail.com) and provide the following information, if possible:

  • Where did you find the document? Who created it? When was it created? Who was the recipient? Which languages did this person speak? Information of this kind can be extremely helpful for a codebreaker.
  • Tell us if we may publish this cryptogram (such as on the internet or in a book like this) or if you want to keep it confidential. We won’t publish anything without the consent of the sender.
  • In case you allow us to publish a cryptogram, tell us if you would like credit for it, and/or if we may mention your name.

Since Klaus is from Germany, will there be a German version of the book?
Sorry, no translations are planned at this time. Most of the encrypted messages in the book are English, and most of the codebreaking techniques are based on properties of the English language, so a one-to-one translation to German doesn’t make sense.

Who drew the cartoons? Are there more?
All were drawn by Klaus, with some input from Elonka. Klaus has published a book of cartoons (in German), called Chief Security Officer. A few episodes have been translated, such as the following:

Have you written anything else?

Yes, you can see a list of our books here.

Who contributed to the book?

We had many excellent proofreaders, and people who provided us information, encrypted items, pictures, and other assistance. Please see the acknowledgements page for a full list.

What is a good beginner book about cryptography?

Of course, we recommend ours, which is perfectly suited for both beginners and experts. We also recommend Simon Singh’s The Codebook. For a detailed overview see the reading list, which includes cryptography books for kids.

What is your opinion about Kryptos?

The fourth part of Kryptos is still unsolved. Nevertheless, Elonka, who is the world’s leading Krypto expert, believes that one day the solution will be found.

What is your opinion about the Voynich Manuscript?

Though numerous alleged solutions of the Voynich Manuscript have been published, we believe that this “book noone can read” is still unsolved. The Voynich Manuscript is, of course, covered in our book.

What is your opinion about the Zodiac Killer Ciphers?

Only the first of four Zodiac Killer cryptograms has been solved. In our book, you can read how this happened. The other three, along with some background information, are covered in our book as unsolved cryptograms.

I have designed a new code system, will you look at it?

Probably not. See Schneier’s paper Memo to the Amateur Cipher Designer.

I have solved a famous cryptogram but no one believes me, can you look at my solution?

There are generally mailing lists for each major unsolved code, we recommend posting your thoughts there. For example, the Kryptos sculpture is discussed at (groups.io), the Voynich Manuscript is discussed at (voynich.nu), etc. You may also wish to post your thoughts at the Cryptograms and Classical Ciphers group on Facebook. There is also a thread on Reddit.

Do you also cover modern cryptology, like AES, RSA, Diffie-Hellman, PGP, etc?

We mention them in passing because of how important they are, but really don’t cover them in this book. Our main focus is on classical ciphers. To learn more about modern cryptology, please see the reading list at .

Will you come speak at our event / school / organization? Or, Can I interview you for something?

Sure. Please send us an email (see the contact page).

How did get into cryptography?


Klaus: When I was a computer science student at the University of Karlsruhe, Germany, in the 1990s, I had to attend a programming class. After the classes “Operating Systems”, “Graphical Data Processing”, “Formal Systems”, and “Algorithms and Data Structures” were either fully booked or didn’t take place in this semester, I willy-nilly took “Cryptography”, though I didn’t know what this was. After the third lesson, I changed my study and career plans.

What is new in cryptography?

Post quantum, user-centred

What is your favorite cipher?

How can I encrypt my files and e-mails?

I want to do what you do. What shall I study?

If I want to work for the NSA. What shall I study?

In your book you said that there is much more than you could cover. What else would you have included if you could?

At one point we realized that our book had 25 percent more content than was contracted. So, we hard to start cutting things. We cut:

  • Enigma
  • Cipher machines
  • Stager cipher
  • Hill climbing examples
  • Success stories
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