And what about SSH?

Posted May 22, 2015 21:04 UTC (Fri) by wahern (subscriber, #37304)
In reply to: And what about SSH? by tialaramex
Parent article: Another crypto downgrade attack: Logjam

In retrospect we would have been better off randomly generating primes for DH rather than using fixed ones. Yes, you may generate a non-strong prime. But the likelihood is extraordinarily low as long as you generate what's called a safe prime. Fortunately, OpenSSL generates safe primes. (See crypto/dh/dh_gen.c.) It's why `openssl dhparam 1024` takes so much longer than `openssl genrsa 1024`.

In other words, just use OpenSSL to generate new DH parameters and move on to improving the rest of your software and infrastructure.

And what about SSH?

Posted May 24, 2015 9:35 UTC (Sun) by reubenhwk (guest, #75803) [Link] (1 responses)

generating a new DH* in OpenSSL can be very slow, especially 1024+ bits. It's not something you really want to do on startup. Better to read the p & g params from a file, then fork off a new process to generate new p & g in the background then write them out when done...

And what about SSH?

Posted May 27, 2015 17:40 UTC (Wed) by flussence (guest, #85566) [Link]

Something seems off here: `openssl dhparam 3072` takes 3-4 minutes for me on a fairly high end Intel server CPU, which is in line with what you said, but the gnutls equivalent `certtool --generate-dh-params --sec-param=high` takes 1-2 *seconds*.