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Flaw found in online encryption method

nytimes.com

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Re: Flaw found in online encryption method

#8
As far as I can tell, the researchers are describing features of particular Key Pairs that have been generated by Users of the RSA algorithm. The 'garbage-in, garbage-out' rule applies. If your RNG sucks, you're going to get weak keys out of it.

Is it harder to generate weak Diffie Hellman parameters using a bad RNG?

Update: Yes, apparently. From the paper: "Cryptosystems such as RSA that require, during key-setup, multiple secrets are more affected by the apparent difficulty to generate proper random values than systems such as Diffie- Hellman (cf. [8]), ElGamal, and (EC)DSA that require a single secret."

That's (mercifully) pretty intuitive.

Re: Flaw found in online encryption method

#9
post #2

interesting that they were able to identify that there was bug without being able to say what it was or how it happened.

Yeah, and I think they did not do a very good job explaining it in the paper. Perhaps they assume more familiarity than I have.

But as far as I can tell, the result is that, of public keys collected "in the wild" show more duplication than should be expected, so the random number generation schemes used are not "random" enough. Is that it, or is there more to the story?

(Edit) No, there's more. I don't quite understand (and don't think they really explain), but somehow they use the fact that there's lots of keys to find ones with common factors, which allows you to factor both of them. This sounds basically like the Euclidean algorithm but I couldn't tell what method they're using to find them.

Re: Flaw found in online encryption method

#10
So out of 6.4M RSA keys they found 12K where for the modulus n = pq, p or q (or both) were used for creating modulus for other key.

So when I give them my public key, they can just scan their database and with chance 0.2% find a key with a modulo that is divisible by mine p or q? Is that how it works?

edit: The K9 business looks very dodgy. When analysing the keys they found "9 primes each of whose 36 pairwise products appears as n". So next time you're factoring an RSA key your best bet is to start with primes from this K9...

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