Security Focus Interviews Damien Miller

An anonymous reader writes "The upcoming version 4.3 of OpenSSH will add support for tunneling allowing you to make a real VPN using OpenSSH without the need for any additional software. This is one of the features discussed in SecurityFocus' interview of OpenSSH developer Damien Miller. The interview touches on, among other things, public key crypto protocols details, timing based attacks and anti-worm measures."

Comments

Yes and no.

[jd]

You are correct, but only as far as you go. It is possible to compress first and then encrypt. Indeed, this is generally regarded as the superior method, precisely because the compression will disguise a lot of the information that cryptography will leave behind.

Secondly, cryptography is generally expensive on the CPU but cryptographic processors exist. Motorola's processor unit (before they spun it off) had a very nice unit called the S1, which could encrypt or decrypt four streams in parallel. They had a very nice manual, describing the complete protocol to communicate with it. Despite this, I never have yet seen a Linux driver for it. A pity, regardless of what you think of the S1, simply because it would have been a good opportunity to win over those who do use such chips.

TCP offload engines are also beginning to come into the picture. When TCP stacks didn't do a whole lot, it cost more to offload than you'd gain by having a co-processor. These days, a glance at the multitude of QoS protocols defined in papers, the staggering range of TCP algorithms in Linux, and the complex interleaving of the Netfilter layers -- it almost has to be better to have all that shoved onto a network processor.

(Notice that I'm including more than just the basic operations here. It's the ENTIRE multitude of layers that is expensive. Linux supports Layer 7 filtering, virtual servers, DCCP. There's even an MPLS patch, if anyone cares to forward-port it to a recent kernel. IGMPv3 isn't cheap, cycle-wise. Nor is IPSec.)

There is also the crypto method to consider, too. RSA is expensive but ECC and NTRU are considerably cheaper. SHA-1 is much slower than TIGER and is not clearly better. Whirlpool is also better than SHA-1 on speed and strength.

I'll also mention that OpenSSH is sub-optimal on the implementation, that there are patches out there to make it faster. I mentioned those the last time OpenSSH became a hot topic. Even if the patches themselves aren't "good enough", they must surely be evidence that it is possible to tighten the code a great deal in places. If nothing else, slow code is more vulnerable to DoS attacks.

I disagree on one point.

[Z00L00K]

There is actually a point in locking out (blacklisting) IP addresses from where a brute force is attempted. This since those bots often try one site at a time and scans for known login/passwords. It isn't that common that an attacker uses several different sources at the same time when attacking a site unless it's a DOS attack.

Blacklisting will at least make it harder for stupid bots.