Warning from OpenSSH Client when connecting to Dropbear SSH Server in OpenWrt: connection is not using a post-quantum key exchange algorithm

Installing and Using OpenWrt
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SSH Server :

dropbear - 2024.86-r1 (opkg pkg)
OpenWrt 24.10.3, r28872-daca7c049b

SSH Client :

OpenSSH_10.2p1, OpenSSL 3.6.0
Arch Linux x86_64

I am currently using ed25519 keys.

Warning Message:

** WARNING: connection is not using a post-quantum key exchange algorithm.
** This session may be vulnerable to "store now, decrypt later" attacks.
** The server may need to be upgraded. See https://openssh.com/pq.html

I connect to some remote OpenWrt devices over their WAN (non standard ports).
Should I be worried ?

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did you see ^ ?

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I am not, quantum computers are not here yet besides why would any one store my traffic for future analysis?
If I was an enemy of state that might change and I would use something like https://datatracker.ietf.org/doc/draft-ietf-sshm-mlkem-hybrid-kex/ :slight_smile:

But Dropbear does not support that yet so you need to install the full SSH server if you are worried and want to use such a key

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If you are not opening SSH to the internet you definitely can ignore that.

If you have SSH open to the internet, ypu probably can ignore the warning unless you think you are a high value target :slight_smile:

You can ways follow the link and generate the new post-quantum keys

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IRL you still need RSA for what is called “network infrastructure”

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I just had a quick look at it seems that Main/Snapshot build has Dropbear 2025.88 with:
CONFIG_DROPBEAR_MLKEM768 CONFIG_DROPBEAR_SNTRUP761
So that should have post quantum keys enabled

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They are.

These are the ones that you do hear about. We cannot tell if there are others (possibly with more qubits) being developed secretly by - whoever.

About storing your traffic: That depends on who “they” are. Governments? Businesses? Criminals who happen to get access to quantum computers? Who knows? Thinking one is “safe because I’m doing nothing wrong” is a fallacy.

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Before people start debating this and getting tin-foil hats... consider that:

  1. Yes, quantum computers do exist, but they are not widely available. The work they do is largely experimental in nature and/or of very high value (i.e. if there are 'secret' ones that are fully operational and owned by governments, they would be cracking the codes of hostile nations and/or very high value targets, not the average person).
  2. The ssh traffic to/from OpenWrt is typically for configuration of the router itself or other ancillary purposes. This is especially true if ssh is only available on your lan (some people will use ssh tunneling as a VPN method, but this is less common).
  3. If ssh is open on your lan only (i.e. the default state), you've got bigger issues if some entity is able to intercept/store your lan traffic, plus the above point really was intended to communicate that the ssh connections to OpenWrt are not usually going to contain much in the way of secrets.
  4. If you are using ssh via the wan (and/or using this for ssh tunneling), this is again likely only an issue if you are a very high value target. But you could change to other encryption methods if you want to be more secure.

I worry more about the general internet activity exposure and surveillance much more than I do about the ssh connection between one of my lan devices and my router. At the time that Snowden revealed the extent of government surveillance capabilities, I didn't worry too much about random individuals because it was too much data for anyone to reasonably sift through unless there was a specific person of interest. With AI, that calculus has changed considerably.

But... because quantum isn't ubiquitous (i.e. it is still mostly research and maybe reserved for very high value workloads) it should be noted that breaking encryption (at the quantum level) is still going to be limited to very special circumstances. This will, of course, change over time (just as my point above about AI), but in late 2025, if your ssh connections to your router (especially over your lan) are being recorded and cryptographically broken, you've got bigger problems on your hands.

All that said, as @egc stated, it should be possible to mitigate this issue with the newest dropbear versions on Main/snapshot and eventually stable releases of OpenWrt.

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