[tor-relays] Re: Post-Quantum Cryptography in Tor's TLS Layer: Help needed!

[Alexander Hansen Færøy via tor-relays <tor-relays@xxxxxxxxxxxxxxxxxxxx>]

Hey Felix,

On 01/03/2026 11.12, Felix via tor-relays wrote:
> Hey
>
> Thanks for the excellent work.
>
> > Out of 9476 scanned relays, ... , 291 were unreachable.
>
> An interesting number for two reasons:
>
> i. Mine are in that group of unreachable relays, still :( Going to bump
> to Libressl 4.3.0 as soon as it is available :) - and functional.
>
> ii. Is it fair to suggest that a max of 291 relays use Libressl out
> of the 9476 being scanned? Besides Libressl is later than Openssl, how
> do we look at this proportion, is it worth to increase the slice?

Yesterday, when I tried to reply to your email, I wrote a longer message about 
how the 291 number roughly matches what I saw in my earlier scan in January 
(~198 relays that were unreachable). While writing the mail, I tried to 
reproduce the result by only scanning George's Serge Bridge Authority relay, 
which I know is OpenBSD with LibreSSL, but I was unable to reach it at all.

It turns out you likely found a bug in our new PQC handshake code! When I use 
the initial version of the scanner, which uses another crypto provider for the 
PQC, it works! We'll get this fixed, but this issue also made me run a new full 
network scan with the old crypto provider here. This scan had no errors from the 
TLS layer. The results are available at https://ahf.me/tor-tls-pqc/2026-03-01/

Good catch here, Felix!

With regard to whether it's a good idea to have a larger proportion of the 
network based on LibreSSL, I will fall back on my usual thought on the network 
diversity question, which is that operators should use what they are most 
comfortable with :-)

The summary of yesterday's scan is as follows:

Scan Stats:
  - 9562 relays were reachable.
  - 158 relays were unreachable.

Cipher Suites:
  - `TLS13_AES_256_GCM_SHA384`: 9352.
  - `TLS13_CHACHA20_POLY1305_SHA256`: 165.
  - `TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384`: 39.
  - `TLS13_AES_128_GCM_SHA256`: 6.

Key Exchange Groups:
  - `X25519`: 5350.
  - `X25519MLKEM768`: 3313.
  - `secp256r1`: 899.

Directory Authorities:
  - 10 out of 10 were reachable.
  - `TLS13_AES_256_GCM_SHA384` was used by all 10.
  - `X25519` was used by 5, and `X25519MLKEM768` was used by 5.

3313 / 9562 * 100.0 = 34.65% of relays are supporting the `X25519MLKEM768` PQC 
handshake in the network right now.

Again, thanks for catching this, Felix!

Cheers,
Alex

--
Alexander Hansen Færøy
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