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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."
For example, if you create a VPN with this latest OpenSSH, a lossy network will hold up your traffic. Despite the fact that TCP/IP will try to continue operating with dropped packets, with OpenSSH if you miss one packet the loss cascades into succeeding packets until the client and server are able to resync or the packet is delivered. This accumulation of tolerances is not a problem with IPsec, which is designed cipherwise to work around occasional packet loss.
Most experts agree the product of the best cryptography will be indistinguishable from random noise. This means that it is difficult to share the benefits of compression with file encryption because random noise compresses very poorly, as anyone who attempts to archive their MP3s of today's artists will attest. Additionally, if you accidentally store your encrypted files amongst files containing random noise you run the risk of generating new data during decryption.
The secret is to understand the technology before you use the technology. The problem with encryption is twofold -- some people are overconfident in what they're using and either lose data or risk more than they would if they were fully informed, and others think it's too difficult a topic to broach and leave themselves open to exploitation by network explorers. Certainly when I was in the second category I became convinced of the problem once I saw tools like 'tcpdump' and 'ethereal'.
Try not. Do or do not, there is no try.
-- Dr. Spock, stardate 2822-3.
OpenSSH just keeps getting better. Not just a great shell client and server, but support for multiple streams, secure tunnels, SCP, SFTP, every authentication method you could want, and finally VPN (the next logical extension). OpenSSH ships with every Linux distribution I can name (well, except embedded ones), the BSDs, and MacOS, and is available for Windows (under Cygwin) and every other major UNIX and UNIX-like OS out there. The code is all available to anyone for any purpose with no real restrictions (other than giving some credit to the developers), so you could include it in any app you make, regardless of license (GPL included). Thanks, everyone who works on this valuable tool. I think I'll go buy a T-shirt
Thank you devs! I've been waiting forever for the ability to do VPN like that. /me builds shrine
Silence is golden... and duct tape is silver.
For those hackers who are already familiar with the forwarding features of ssh (-L, -R and -d options), and who are wondering what the hell is this new "support for tunneling", here is a hacker summary. Quoting TFA:
Tun(4) interfaces are indeed very convenient. That's all folks !
$ telnet 293.myremotepc.com
login: mr_moo
password: moowoo
> lynx slashdot.org
ssh is great and all but telnet is secure enough for me as far as __ALL_YOUR_BASE_ARE_BELONG_TO_US__ wha? who typed that? what's __H4X0RZ_4EVA!__
CONNECTION TERMINATED.
Anons need not reply. Questions end with a question mark.
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.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
Blacklisting will at least make it harder for stupid bots.
If builders built buildings the way programmers wrote programs, then the first woodpecker would destroy civilization.
Anyone seen this before?:
http://www.hamachi.cc/
Loos like a better way of doing VPN.. though ssh with in built vpn is going to be nice...
"Consider how lucky you are that life has been good to you so far. Alternatively, if life hasn't been good to you so far
SSH tunnels and VPN can already today be done using ssh and pppd. i have used it for many years. It is still a stupid idea and useless for other things than toy networks.
SSH uses TCP as transport. You should NOT transport TCP/ip ontop of TCP. TCP over TCP has well known and well documented poor performance characteristics.
Google for TCP over TCP to find any number of researchpapers on why this just doesnt work, or try running IP traffic yourself across an SSH tunnel and find out first hand why TCP over TCP just dont work well.
Maybe, I hope, they plan to add a new SSH mode that uses UDP and will use UDP-SSH as basis for the tunnel. That would work. But you can neveruse more than one single TCP layer in any stack. If not (i.e. they plan to tunnel traffic atop a TCP ssh session) it will fail and they will learn.
Another statistic suggests that more than 80% of the SSH servers on the Internet run OpenSSH. I'm wondering if you have ever verified which version they are running, and what is the average behaviour of an OpenSSH administrator. Does people update the server as soon as a new release is available?
Damien Miller: Funny you mention this, we just completed another version survey with the assistance of Mark Uemura from OpenBSD Support Japan. The results of this should be going up on OpenSSH.com soon.
I don't have detailed OpenSSH version histories for usage surveys before last year's. Certainly the use of paleolithic versions (such as 2.x) is very infrequent, but beyond this it is difficult to tell how quickly users update - many vendors will keep relatively ancient versions (such as 3.1p1) on life-support with spot security fixes. This will avoid known security problems, but it doesn't give their users the benefit of any of the proactive work that we do, nor any of the new features.
It is worth noting that OpenBSD, which has a very conservative policy on its stable trees, typically updates supported OpenBSD releases to the latest OpenSSH version when it is released.
Being very popular means also being a good platform for a worm. Did you adopt any specific measures to fight automated attacks?
Damien Miller: Privilege separation alone probably makes a worm targeting a bug in sshd impractical. An attacker would need to break into the unprivileged sshd process that deals with network communications and, because this just gives them access to an unprivileged and chrooted account, then exploit a second vulnerability to either break the privileged monitor sshd or escalate privilege via a kernel bug. This would add a fair amount of complexity, fragility and size to a worm - it would probably need to implement a fair chunk of the SSH protocol just to propagate.
We also implemented self re-execution at the c2k4 Hackathon. This changes sshd so that instead of forking to accept a new connection, it executes a separate sshd process to handle it. This ensures that any run-time randomizations are reapplied to each new connection, including ProPolice/SSP stack canary values, shared library randomizations, malloc randomizations, stack gap randomizations, etc.
Without re-exec, all sshd child processes would share the same randomizations. This would allow an attacker to exhaustively search for the right offsets and values for their exploit by making many connections (millions probably) to the server. With re-exec, each time they connect the values will all be different so there is no guarantee that they will ever stumble upon the right combination.
Another security improvement, just introduced in openssh-4.2 was the "zlib@openssh.com" compression method. This was an idea that Markus Friedl had after the last zlib vulnerability was published.
The SSH protocol has supported zlib compression for a long time, but the standard "zlib" protocol method requires this to be started early in the protocol: after key exchange, but (critically) before user authentication successfully completed. This exposes the compression code to unauthenticated users.
Our solution is to define a new compression method that still performs zlib compression, but delays its start until after user authentication has finished, so only authenticated users get to see it. This is another significant reduction in attack surface with effectively zero performance impact. This also makes the writing of a worm that targets the zlib code in OpenSSH impossible.
Did you develop any measure to fight timing based attacks?
Damien Miller: There are two classes of timing attacks, one of which matters and the other is not so important.
The not so important timing attacks allow active detection of which usernames are valid by differing timings i
>>You just can not run TCP over TCP. It just doesnt work. Actually this is not true. TCP over TCP is a problem when you have packet delay and the back off times on the redundant layers cause a meltdown and stop your connection. When congestion is at a reasonable level, this will not happen. So TCP over TCP works fairly well if you don't have a near capacity link.
Damien, do you think that catchers will start using the inside protector any time soon?
When the code is good, clean, free and something the developers want.
I'm sick of following my dreams - I'm just going to ask them where they're going and hook up with them later.
You're spouting complete nonsense. A secure block cipher in a secure mode of operation revelals nothing about the similarities between files. Loock up CBC mode on Google - a large random initialization vector is used to ensure that identical (or similar) plaintext blocks encrypt completely differently. I also suggest a thorough reading of Applied Cryptography by Bruce Schneier.
OpenPGP, for example, uses gzip compression before encryption with every file. Yet PGP is widely considered very secure. Why? Because a secure mode of operation for the cipher (AES, 3DES, whatever) is used, with a random IV that ensures even identical files produce completely different ciphertext.