# The D’Agapeyeff Cipher, Unsolved for 80 Years!

[Image courtesy of Derek Bruff.org.]

One of my all-time favorite cryptography stories comes from the book The Spy That Couldn’t Spell, a true-life espionage story about a dyslexic man who hid, then encrypted the locations of, thousands of pages of sensitive documents he had stolen from the U.S government.

Why is it one of my favorite stories? Well, because the man in question FORGOT one of the cipher words he used to encrypt the location of his caches.

And it sort of unravels your master plan when you can’t remember a key element of it.

Amazingly enough, this isn’t the only example of a self-trained cryptographer who forgot how to solve his own creation. In fact, one example of this very dilemma remains one of the most famous unsolved codes and ciphers in the world:

The D’Agapeyeff Cipher.

This is the D’Agapeyeff Cipher. This seemingly simple list of numbers contains a secret message. The only problem is… the creator, Alexander D’Agapeyeff, can’t remember how to decrypt it.

When he published a starter book on cryptography — Codes and Ciphers, first edition — D’Agapeyeff included this chain of 5-digit number bundles as a final challenge for the readers to unravel.

One of the first steps many aspiring cryptographers take is to break the numbers down into pairs instead of groups of five:

One result of this is the pattern that every pair has 6, 7, 8, 9, or 0 in the tens column and 1, 2, 3, 4, or 5 in the ones column, which doesn’t seem like a coincidence.

And see those sequences where the same number appears three times in a row? Some cryptographers believe that is also not a coincidence.

Then, they cut off the two double-zero pairings at the end — because they believe they were nulls, empty space-filling characters simply designed to fit the 5-letter groupings pattern of the original code as a way to throw off codecrackers. (And, to be fair, D’Agapeyeff himself wrote about null entries in the book Codes and Ciphers.)

If you remove those double-zero pairings, you can arrange the numbers into a 14×14 pairing grid, like so:

See those sequences where the same number appears three times in a row? More of them now.

Many cryptographers consider this to be the true starting point of cracking the D’Agapeyeff Cipher.

But then what?

Some believe that the key to solving the grid lies in the Polybius Square, another encryption device mentioned by D’Agapeyeff.

Essentially, you place the alphabet into a 5×5 grid, and use those numbers to encrypt the letters. Here’s a straightforward example:

In this case, the word PUZZLE would be 35 45 55 55 31 15.

Another way to use the cipher is to pick a keyword to start it. For instance, if you chose POLYBIUS as the key word, then you go across, then down, writing POLYBIUS and then the rest of the unused letters of the alphabet in order, like so:

Instead of 1-5 both across and down, you could do 1-5 across the top and 6-0 across the side, reflecting the pairings in the D’Agapeyeff Cipher.

Or, as someone pointed out, perhaps we’re thinking in the wrong language. Triple-letters are uncommon in English words, but more common in Russian words, and D’Agapeyeff was Russian born.

Overlooking simple things like that can make you miss crucial ways into an encrypted message.

So, do you have any thoughts on how to solve this 80-year-old encrypted challenge, fellow puzzlers? Let us know in the comments section below! We’d love to hear from you.

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