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<tt>We should definitely change to per peer PSKs.<br>
Following </tt><tt><tt>Storömberg's observations, the following </tt>points
may also be worth considering:<br>
</tt><tt><br>
1. Partial deployment<br>
<br>
Per peer PSK allows organization to deploy PSK to a subset of
peers and have a smooth transition should they wish to implement
it later.<br>
<br>
2. Compromise of endpoints<br>
<br>
All it takes is one compromised endpoint and PQ secrecy fails
completely.<br>
If an employee ever leaves his laptop unencrypted and unattended,
the PQ secrecy of all the </tt><tt><tt>corporations</tt> VPN
connections could be lost.<br>
<br>
Furthermore, if an administrator suspects this may be the case,<br>
he has to deploy new keys to all endpoints in a PQ secure manner
(e.g sending them over HTTPS is meaningless);<br>
he most likely has to physically install the new PSK on every
client!<br>
<br>
In case of compromise, the peers public key must be updated
regardless and updating the per peer PSK along with it seems a
manageable task.<br>
<br>
3. Disclosure of data under a warrant<br>
<br>
Suppose the </tt><tt><tt>organization</tt> deploying Wireguard is
forced to decrypt the data to/from a single peer.<br>
Currently this is not possible, because of forward secrecy,
however in a post-quantum setting it would be.<br>
Limiting the disclosure to a single peer is substantially harder
with a globally shared PSK.<br>
<b><br>
</b>Periodically rotating the PSKs and completely avoiding the
case above is much easier if the PSK is per peer.<br>
</tt><tt><b><br>
</b>4. Public VPN<b><br>
<br>
</b>If Wireguard is deployed as a public VPN, there is no hope of
PQ security with a global PSK.<br>
In the case of a per peer PSK, this may be achieved by meeting in
person or exchanging the PSK with PQ crypto, e.g<br>
the overhead of McEliece may be acceptable, since the PSK is only
transfered once.<br>
<br>
5. Users and secrets<b><br>
</b><br>
Since the key is shared, you can count on Alice asking Bob for his
VPN configuration, <br>
you can also count on Bob sending said configuration over email.<br>
Again the PQ security for the entire organization is lost.<br>
<br>
As the organization grows, the probability of such an event goes
to 1.<br>
<br>
Regards,<br>
Mathias<br>
</tt>
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