Why not “Why not WireGuard?”

https://tailscale.com/blog/why-not-why-not-wireguard/

by Foxboron • 6 years ago

174 41 6 years ago

brobinson3• 6 years ago

Glad someone did a rebuttal of that article. I came across it a few days ago and was shocked to discover it was by the guy behind ipfire, which I had previously heard good things about.

wmf• 6 years ago

When somebody absolutely positively cannot give up their hardware VPN box yet gets inundated with "WireGuard or die", that's the kind of bitter defensiveness that results. It's just human nature.

willis936• 6 years ago

Who is giving “WireGuard or die” to people with hardware VPNs right now? It isn’t in any LTS releases right now and won’t be for another year.

geofft3• 6 years ago

Yes, agree - the original article displays such a bad understanding of security that customers should avoid taking any operational advice, security-related or not, from the person who wrote it.

The author of the original article seems to be making the following assumptions:

- "Secure" is only about what protocols you support, and not about the quality of implementation, whether the protocols are implemented accurately, etc. In the author's world, Heartbleed (which was introduced as part of DTLS, part of Cisco's VPN implementation) doesn't exist, the Pulse Secure vulnerability that left Travelex completely non-operational doesn't exist, etc.

- That said, "3DES with MD5" is a good cryptographic protocol to use, and you should avoid fancier things like "AES-256 with SHA1."

- You should only consider using black boxes from companies like Cisco and Juniper (authors of Pulse Secure). If it's not compatible with those appliances, it's not worth using.

- You can't ever upgrade software in a reliable fashion. Everyone is running old, unpatched versions of software, and it's better for that unpatched software with all the well-known zero-days to connect to your corporate network than to be blocked from connecting.

- You should directly connect your internal network to "third parties that you do not control," and you should let those third parties dictate your software choices instead of vice versa.

In this world, you have nothing other than constant disasters. I guess it's good for job security, especially for someone whose job is professional support for IPsec.

It's a shame it needed debunking, but I'm glad someone did.

Spivak4• 6 years ago

I agree with his point about software upgrades. Everyone is running old unpatched versions of software! WireGuard just externalities the messy upgrade process that will accumulate over time when you have to support devices and services that only support specific versions of the protocol. You’ll end up having to run multiple WG instances in the “transition period” that never actually ends rather than just negotiating the most secure thing you both support. And you can still cut people off from broken algos.

Having compatibility with the major vendors in the space is a real advantage because it’s a de facto standard I can get other companies and partners to agree on because they’re probably running one of those black boxes. You don’t have actually use any of them, but you will get a call down the road to interface with one of them.

I think the main thing is that WireGuard is a beautiful clean protocol that is about to get buried under piles of shoddy middleware to deal with the messy real world.

Spooky23• 6 years ago

I agree the original article was really dumb, and sounded like it was written by an enterprise network guy who has only worked with and been trained by big vendors.

That said, the fatal flaw of Wireguard is the crypto model. Nobody who interacts with the US government, regulated US industries, or some F500 will be able to use it because of the fixed algorithm choice, which isn’t possibly FIPS 140-2 validatable. You’ll always need that Cisco/Pulse/whatever box.

That may be a feature for some, but it kneecaps the possibility of it being as ubiquitous as it might be otherwise.

thoraway10102• 6 years ago

I just wish the wireguard folks did IP6v2 :)

Kidding (kind of)!

jabl• 6 years ago

I recall skimming some recent(-ish) IPv6 overview RFC which was an update to an older RFC, ("IPv6 architecture", or something like that, maybe?) and IPSec has been demoted from necessary to optional.

So it's not entirely impossible IPSec will eventually fade into obscurity.

MayeulC• 6 years ago

I quite like Yggdrasil's [1] approach, and there are other alternatives. Of course, it doesn't fix everything, but with many project working on different aspects of networking, we might get back to an "internet" that's closer to a mesh between non-interoperable networks (GNU net, cjdns, private VPN-backed LANs, zigbee, etc).

Because, on your local network, you can run whatever you want (but it better be ipv6-aware software using DNS, it's easier to fool like NAT64 or yggdrasil do).

[1] https://yggdrasil-network.github.io/

thoraway10102• 6 years ago

Thanks for this - I'm not an expert at all in the networking space side of things, but even dabbling with ipsec / ipv6 combos made my head spin coming from an ipv4 background.

Basically I was left with the idea - how in the world is the gigantic set of interlocking RFCs (at least to me IPv6 seems to involve a lot of complex stuff) the best way to network these days.

brunoqc• 6 years ago

I can't wait for the tailscale app for Android.

If I die from covid before I get it I'll be very upset.

dfcarney• 6 years ago

(Co-founder here). It's coming, I promise. I'm as excited as you are. We wanted to iron out the kinks on mobile (i.e. iOS) before duplicating them on another platform. Thankfully, we're past that point now.

XelNika5• 6 years ago

This section of the article is confusing at first because it talks about “road warrior” users (who generally have dynamic IP addresses) not being supported by WireGuard. But this is not true; standard WireGuard happily works as long as as least one end (usually the central VPN concentrator) has a static IP address.

Maybe I don't understand the issue to be solved (I was unfamiliar with the 'road warrior' term so I looked it up [1]), but I think both Avery Pennarun and Michael Tremer misunderstood what WireGuard is capable of. WireGuard works just fine when the physical network interfaces have dynamic IPs (on both ends even). You can use the basic wg or wg-quick tools to create a VPN server on a server with a dynamic IP and have clients connect from dynamic IPs. However, all the tunnel IPs must be static unlike e.g. OpenVPN where the server gives the client a tunnel IP during authentication.

(for example, so you can get to an office network whose home connection uses dynamic DNS). It’s true that plain WireGuard does not support this configuration out of the box.

I have done literally that for over a year now. I cannot think of a way to interpret this that would make Avery's claims true.

Someday, WireGuard will need to be upgraded to support a second cipher suite. When this happens, users will be able to configure it peer-by-peer to allow one cipher suite or the other, or both, exactly as they would with any other VPN.

That is not how I interpret what Donenfeld has said [2] about the future of WireGuard. I believe the software will get a v2 without backwards compatibility. However, even that is a non-issue because sysadmins can run both protocols in parallel during the transition.

[1] https://en.wikipedia.org/wiki/Road_warrior_%28computing%29

[2] Page 3 of https://www.wireguard.com/papers/wireguard.pdf

CalChris3• 6 years ago

Yes, it seemed to me that Donenfeld was pretty opinionated about 'updating breaks compatibility'. Donenfeld is the anti-Torvalds: we will break user space. This is the closest quote I could find.

  If holes are found in the underlying primitives,
  all endpoints will be required to update.

Unlike IP packets, struct message_header doesn't even have a version number. I suppose type could be used for that since it's 32b.

An interesting question is how will this play out with Wireguard going into the Linux kernel itself.

XelNika5• 6 years ago

Breaking user space might not be popular with users, but it makes sense for security. Besides, anyone could build protocol negotiation on top of WireGuard v1/v2 if they wanted to.

I'm not a kernel dev, but WireGuard v2 will probably be implemented as a separate kernel module so they can coexist. It makes sense to do it that way since they're practically entirely separate protocols.

nickodell2• 6 years ago

In contrast, a hypothetical WireGuard protocol v2 can offer just two suites, the old one and the new one, with simple advice: use the new one if you can, and allow the old one for old nodes until they’re upgraded. There’s nothing unusual about this, except you don’t need to be a cryptography expert to configure it.

I don't think this is going to be as simple as the author thinks. Look at Git's migration away from SHA1. There was no designed mechanism for switching hash functions, and lots of code assumed 20-byte hashes. Three years after the first SHA1 collision was discovered, Git has not switched to a new hash function. I don't mean to be alarmist - no one has created a practical attack on Git objects, but the time to switch cryptographic primitives is when they start showing weakness, not after they are definitely broken.

IPSec has a standard method for supporting multiple cipher suites, and negotiating a common suite. It might be very complicated, but we have no way of comparing it to WireGuard, because WireGuard doesn't implement the same feature.

apenwarr2• 6 years ago

Persistent data structures (like git) are way harder to update than non-persistent structures (like ephemeral network packets).

Hypothetical WireGuard v2 packets will simply not parse as WireGuard v1 packets; they can't be decrypted as WireGuard v1. And vice versa. It's therefore trivial to have both protocols coexist, even on the same UDP port, without any negotiation whatsoever. You simply need to discard packets that don't decrypt, which is what WireGuard already does.

It's dangerous to include a downgrade-capable negotiation in your VPN protocol. I'm glad they left that out of WireGuard.

nickodell2• 6 years ago

It's therefore trivial to have both protocols coexist, even on the same UDP port, without any negotiation whatsoever. You simply need to discard packets that don't decrypt, which is what WireGuard already does.

If both ends will automatically fall back to v1, how do you prevent protocol downgrade attacks? An adversary dropping v2 packets looks exactly like the other end not supporting v2 packets.

It's dangerous to include a downgrade-capable negotiation in your VPN protocol.

I agree. It's a hard problem to solve. But it's going to have to be solved eventually.

AgentME2• 6 years ago

SHA1 was already found to be weak when git was made. Linus would have done better to use a strong hashing algorithm to begin with than to try to incorporate cryptographic agility. It was only found to be weak a few months before git's release though.

Regardless, I think cryptographic agility makes a lot more sense for a storage format like git than it does for a wire format. A shared repo being upgraded from gitv1 to an incompatible gitv2 would need everyone to switch versions at once. With WireGuard, a server could offer support for both v1 and v2 clients, then both v1 and v2 clients can connect to it at the same time, and clients can upgrade on their own schedule. The protocol doesn't have to make any special allowances, like making any data structures interpretable by both, besides to have both v1 and v2 on different ports or have different initial connection messages.

WireGuard was developed in response to protocols like IPSec, OpenVPN, and TLS, which emphasized configurability and cryptographic agility to a fault. Not only were they hard to use and easy to misconfigure, but each one of them were at times vulnerable to downgrade attacks because of subtle bugs in their ability to be configured. It's better to be able to have few code paths and verify they all work as expected, than it is to have many code paths, only verify the happy path, and hope that there's no way for users to fall down an unstudied insecure path by their own fault or because of attackers.

tptacek3• 6 years ago

Doesn't agility make even less sense in a file format? Browsers, for instance, don't need format agility to tell a PNG from a JPG. Meanwhile, PDF tried to provide exactly that capability, and it is a world-historic security disaster. The cryptographic equivalent is PGP, and... I rest my case.

hncensorsnonpc• 6 years ago

In his "L.T. on git" talk at google Torvalds said he used SHA1 not for security, that that would be elsewhere but he called sha1 the best (I think even most secure) hash out there. The serious most well know sha1 flaw was not discovered at that time AFAIK so not sure what you mean by already known as weak. And the fact that 3 years later git has not been broken proves its security does not rely on sha1 alone. I did not even know they are working on a change but good and makes sense of course.

nikisweeting• 6 years ago

Finally, I've been waiting for someone to write a proper response debunking that original article. I was surprised when it got as much attention as it did, since it clearly seemed out of date.

Why not “Why not WireGuard?”

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