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Comment by madspindel | Hacker News Reader

Why not just use PresharedKey in Wireguard?

Using a PSK alone doesn't make WireGuard quantum-safe. The security of the key exchange mechanism in WireGuard, which relies on the Diffie-Hellman protocol, is still vulnerable to quantum attacks.

If an attacker were to obtain the PSK and use a quantum computer to break the Diffie-Hellman key exchange, they would be able to decrypt the VPN traffic.

This is currently the thought-process and main reason behind why PQWG (Post Quantum Wireguard) are actively being researched [1].

[1] https://ieeexplore.ieee.org/document/9519445/

> Using a PSK alone doesn't make WireGuard quantum-safe.

Not sure what you're trying to say here. If you share the PSK out-of-band, securely, then wireguard is quantum resistant (I wouldn't say quantum-safe, because I'm not that optimistic).

> If an attacker were to obtain the PSK

Indeed if the attacker obtains the PSK then obviously the PSK isn't going to help you.

Wireguard explicitly mentions that mixing in a PSK provides post-quantum security [1].

1: https://www.wireguard.com/protocol/

Please be careful in your quoting. The page you linked says "post-quantum resistance", not "post-quantum security" (which would be a much stronger claim).

> If an attacker were to obtain the PSK

I believe it is traditional, in most threat models, to assume that the attacker doesn't have your private keys.

That's what they're doing, generating a key using post-quantum crypto and using it as the PSK - from TFA: "The tool establishes a symmetric key and provides it to WireGuard. Since it supplies WireGuard with key through the PSK feature using Rosenpass+WireGuard is cryptographically no less secure than using WireGuard on its own ("hybrid security"). Rosenpass refreshes the symmetric key every two minutes."

Author here;

We are :) Rosenpass is a fancy way of generating a PSK for WireGuard.

You still can. The problem arises when you don't actually wanna pre-share the key, and you still want post-quantum forward secrecy. Then you need a PQ KEM like McEliece or Kyber to run a PQ-secure key establishment.

That doesn't solve the key management problem, it just defines it as out-of-scope, since you still need to exchange that preshared key outside Wireguard.

Why not just use preshared keys in all VPNs like IPSEC?

Because key exchange and key rotation is a huge problem.

Is it any harder than exchanging and rotating asymmetric keys?

You can do that on top of a public/private keypair, too.

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