After Weeks of Trying, UK Cryptographers Fail To Crack WWII Code

An anonymous reader writes "A dead pigeon discovered a few weeks ago in a UK chimney may be able to provide new answers to the secrets of World War II. Unfortunately, British cryptographers at the country's Government Communications Headquarters (GCHQ) have been unable to crack the code encrypting a message the bird was tasked with sending and say they are confident it cannot be decoded 'without access to the original cryptographic material.'"

Comments

No surprise there

[Anonymous Coward]

Given that the original message looks supiciously like it was encoded with a one time pad, it's really not at all surprising that they can't crack it without the relevant pad. Which was probably destroyed a long time ago.

Re:No surprise there

[BitterOak]

Your citation is incomplete. Key reuse is one way to weaken the encoding without forking over the key itself, though this needs multiple messages encoded with the same key.

If you've re-used a key, you're no longer using a one time pad. (Hint: Why do you think it's called a one time pad? [emphasis mine])

Re:No surprise there

[v1]

Your citation is incomplete. Key reuse is one way to weaken the encoding

Please re-read the entire cited text. Pay special attention to "never reused in whole or part"

(also, even a single re-use can completely compromise all other messages that used a given pad, if the plaintext of a single message encoded with that pad is discovered by other means)

I'm not a cryptoanalyst, but I play one on TV

Re:No surprise there

[0123456]

You still don't get it.

You might know that the message is 'The Commies have XXX tanks' where XXX is a number, but if the pad is correctly generated and used, the XXX can decode to any three digit number whatsoever, so that knowledge gives you no information at all.

Re:No surprise there

[hawguy]

While that is true, you will note that i said probable content. Yes there are any number of equally valid decodings. However few will make sense in the context in which they were sent.

The assertion that there are any number of possible decodings only works when you have zero knowledge of expected content, and as such its a tired and juvenile objection.

It's not that there are "any number of equally valid decodings", but there is every possible decoding. If the word "APPLE" is encypted with a one-time pad into "XYZZY", there are potential one-time pads that will decrypt that string into "APPLE", "IPHONE", "STEVE", "WINMO", "GOOGL", "ANDRD", "SBRIN", "LPAGE", "BILLG", etc.

How do you know which of those is the "valid decoding"? How does your knowledge of expected content help you?

Re:No surprise there

[ceoyoyo]

He's right, you clearly don't understand how one time pads work.

With a properly used one time pad, ANY message (of the same length) is equally valid. Typically you salt the message with some nonsense or whitespaces too, so any message of length = the length of the encrypted message is possible.

So you can make up any message you want, gibberish or real words, and you have no idea if it's the real message or not. You cannot use frequency analysis, dictionary attacks, content hints, or anything else against a properly used one time pad.

You're thinking of simpler encryption algorithms that DON'T use completely random pads. Things like Enigma. If you know something of the content of the message that can help immensely in decrypting those messages, but again, prior knowledge, guesses or whatever have no effect on the security of a properly used OTP.