Leonardo invented rudimentary public key encryption?

Of course this is referring to Dan Brown’s latest best selling novel, The Da Vinci Code. Since this is GQ, I’m not going to review the book but rather ask a question which I think is sufficiently “factual” for placing it here.

Brown states that Leonardo da Vinci invented a rudimentary form of public jey encryption centuries ago. Apparently he’s referring to a device called “cryptex,” basically a combination-lock container where you can store documents that get destroyed if someone attempts to open it without knowing the proper number.

Now I’m not a cryptologist, but AFAIK public key encryption means you have separate keys for encrypting and decrypting your message, so you can publish the former and keep the latter secret. Unlike in symmetric encryption, this means everybody can send you a coded message that only you and nobody else will be able to read.

I don’t see how the cryptexes, that play a vital role in the novel, can properly described as any form of public key encryption. So there are three possibilities:
(1) With the statement about Leonardo’s invention, Brown is not referring to the cryptex but to some other good idea LDV had;
(2) the statement is crap;
(3) my understanding of public key encryption is wrong.

What’s up?

The Da Vinci Code was a fast entertain read but as far as the encryption stuff in it goes Brown is talking out his ass.

Unsurprisingly, it’s statement 2.

Encrpytion is, well, encryption.

Locking a piece of paper in a boby trapped box is not.

NB if you placed the cryptex in a freezer for a few hours, you could easily open it with a hammer :rolleyes:

So, was there anything before the 20th century that could adequately described as “a rudimentary form of public key encryption?”

As far as physical devices are concerned, Brown’s cryptex or any other self-locking box might be analogous to public-key encryption. The point of public-key encryption is that anyone can encrypt a message using your public key, but only the owner of that key (who has the other half of the key pair) can decrypt. Any self-locking box functions the same way. If you have a strongbox and an open padlock, anyone can lock something up and only the one with the key can unlock it. It’s kind of a pointless analogy to compare that to public-key crypto, but this is a novel you’re talking about.

As far as actual ciphers are concerned and AFAIK, there is no historical public-key encryption. Asymmetric encryption was invented in the 70’s by Diffie and Hellman, and independently by Merkle. The very concept that you could have key pairs that worked this way was their major contribution.