Comment by acmegeek | Hacker News Reader

Comment by acmegeek | Hacker News Reader

Well, compared to Bruce's Blowfish, it too is symmetric with a variable key length. What is different about ColorBlynd is that the block length can vary and the number of blocks within the key varies as well.

What this does is add a "meta key" beyond simply knowing the key. The meta key includes how the key is broken down into blocks. And the number of blocks is used during each round relative to the block length.

So if you know the exact key, but don't know how many blocks there are or how many bits per block, you wouldn't know that you had the entire key.

The whole color deal is a neat way to transport the key and the cipertext, but it isn't integral to the algorithm.

The actual algorithm can be succinctly described in 4 sentences.

I'd definitely like to have Bruce look at it, but I'm not sure how to convince him to check it out. If anybody here knows him personally and thinks this might be worth his time, please forward him this thread.

If I understand correctly, what you call the "meta key" is just a part of the key.

Well, yes, the "meta" part is just how the actual key is broken down. What may be different is that decryption involves more than just figuring out the values for the key, but also its breakdown.

For example, if the bit length breakdown of each key chunk was 17, 15, 23, 12, 20, 19, 22 you would have a 128 bit key. But its not as "simple" as determining the 128 bits. There are 7 key chunks, and the length of each key chunk and the order of their bit length is essential to decryption.

The same key might be guessed with 6 chunks of different bit lengths. This won't decrypt it and in fact it won't even come close or give any indication that it was the correct key sequence.

So, this is what I mean by a "meta" key. There is an additional "dimension" to the key, this dimension means that there are an additional few magnitudes in the keyspace than simply the bit length.

So, in a simpler scenario, a 32 bit key, which normally would be pretty easy to crack, is much harder if you also have to determine if it breaks down: 5-13-9-5 or 17-15 or 9-32 or 5-7-3-6-11 or... The number of permutations are staggering.

Is there another cryptosystem that uses something similar?

Just e-mail him. He actually reads and responds :)

Reply on news.ycombinator.com