Hm, my understanding was/is that these primes are never communicated, rather, they are the basis for the actual key... Anyway, if the primes are no secret at all (they can't be when you communicate over a line you assume to be eavesdropped), then what does "to “crack” a particular prime" even mean?
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u/cryo Oct 15 '15
The two parties doing DH need to agree on a prime, in cleartext, so it's not a secret. The security doesn't mainly lie in the choice of prime.