Mailinglist Archive: opensuse-security (757 mails)

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Re: [suse-security] which cipher for ssh2
  • From: "Kurt Seifried" <listuser@xxxxxxxxxxxx>
  • Date: Fri, 25 Jan 2002 02:44:39 -0700
  • Message-id: <001f01c1a584$e85168c0$6400030a@xxxxxxxxxxxx>
> I'm not out for an argument and, as I said, the 80/90 bits figure isn't
from
> me and it's from memory. If you want, I can forward your mail to my
> colleague as a question.

Wasn't arguing, was just making sure people understand that an 80 bit key, a
90 bit key and a 112 bit key are _SIGNIFICANTLY_ different (i.e. not just 10
times harder), something many people have getting a grasp on (2^10 is easy,
1024, but a difference of 3^32 which is 4billion+? 4billion is a beeeeeg
number, I can't imagine 4 billion of anything in a concrete manner). As well
any reasonably fast keybreaking typically requires absurdly (for now
anyways) fast key factoring systems to brute force it. We're just getting
seriously into terraflops, let alone a machine capable of terra-operations
that would require many many flops =).

> Don't confuse asymettric and symmetric key lengths, though. The latter are
> currently no higher than 320 bits, while those of the main proponents of
the
> former, namely RSA or DH/DSA, aren't lower than 512 bits and should be
> 1024+. RSA is worthless unless the primes are large enough.

Dah. But then you can do things like 3des which is usually 2 keys for an
effective length of 112, but the attacker has to do 3 crypto operations, so
an attack becomes expensive. Imagine the keyscape of 3pgp (yes I know pgp is
a program and not the algorithm used for crypto, but you get the idea ;).

99 times out of 100 with modern crypto it's weak passphase/mistake in key
recovery/creation/etc that does it in, the math is rarely wrong, unless it's
a closed system or amateur system (something to be learned from that I
think).

> Cheers
> Tobias

-Kurt


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