On Fri, Jul 31, 2015 at 11:31:08PM +0000, p...@securecottage.com wrote: > I have checked through the key generation code of the openssl ssl code.
Not carefully enough... > I > hacked it to report the greatest common divisor of p-1 and q-1. I then ran > 100 key generations. It only had greatest common divisors of 2, 4 , 8, and > 16. There were no other primes reported besides small powers of 2. The reason is that all the pseudo-primes generated for testing are sieved to avoid numbers that are congruent to either 0 or 1 mod p for each of the first 2048 primes other than 2 (2 is avoided by forcing the low bit to 1). Thus any odd factor of (p-1) or (q-1) is necessarily larger than the 2048th prime or 17863. To see an appreciable chance of such a common factor you need O(20000) trials. While a check to avoid gcd(p-1, q-1) > 2 is not too expensive, it is not clear that it is worth the trouble. Perhaps it should be done anyway, just because we can, but I am not convinced. -- Viktor. _______________________________________________ openssl-dev mailing list To unsubscribe: https://mta.openssl.org/mailman/listinfo/openssl-dev