Hacker News Reader

Comment by daveloyall | Hacker News Reader

I also assume it is a good reason. I'm curious, what is that reason?

From the article...

    > Unlike prime numbers in RSA keys, which are always
    > supposed to be unique, certain Diffie-Hellman primes
    > are extremely common.

Does anyone know why?

View on HN

Basically, because people thought it was safe. It didn't seem significant to use the same prime since the key exchange process involves both Alice and Bob generating a secret. Solving the discrete logarithm of g^a mod p was still thought to be intractable given a large enough (1024bits) p.

As to the technical reason why the DH parameters were reused - speed and efficiency. A DH key exchange would take longer if you had to generate those parameters each time.

I agree with your comment, but I'd like to add that if you speedily/efficiently do the wrong thing, it's no good. The first step of optimization is correctness.

Reply on news.ycombinator.com