Causes and fixes

Every report has one cause code. It’s stable across versions, so scans, the GitHub Action and Flarebox’s history compare by it.

Post-quantum

Code	Meaning	In the study
pq-preferred	Negotiates X25519MLKEM768, and picks it even when the client’s first key share is classical	1,038
pq	Negotiates it when the client offers it first	139
pq-split-dropped	Post-quantum, but a PQ hello split across TCP segments goes unanswered	0
pq-other-group	0.2.0: post-quantum only with SecP256r1MLKEM768, SecP384r1MLKEM1024 or pure ML-KEM, not X25519MLKEM768. From the group survey	not measured (0.2.0)

Not post-quantum

Counts are out of the 3,439 origins in the study that answered TLS but weren’t post-quantum.

Code	Meaning	In the study	Fix shown in the fix lab?
no-mlkem	TLS 1.3, but no ML-KEM: the TLS library predates it, or the group list leaves it out	2,108 (61.3%)	Yes
tls12-only	No TLS 1.3 at all, so no hybrid key exchange	1,146 (33.3%)	Yes
pinned-nist	As no-mlkem, and it prefers NIST P-curves, a hand-written curve list	109 (3.2%)	Yes
no-tls	TLS alerts to every hello	41 (1.2%)	—
large-hello-dropped	A middlebox drops any ClientHello of PQ size split across segments	32 (0.9%)	Yes
pq-group-rejected	Something in the path breaks on the X25519MLKEM768 codepoint itself	2 (0.1%)	Yes
kyber-draft-only	Only the pre-standard X25519Kyber768Draft00	1	Unit tests only

No answer

Code	Meaning
no-reply	Only timeouts or resets: down, firewalled or rate-limiting
connect-failed	Couldn’t open a connection

In the study, 523 of 5,139 probed origins gave no TLS answer on port 443 and aren’t counted in any share.

SSH

The SSH check has its own codes: ssh-mlkem, ssh-sntrup-only, ssh-draft-only, ssh-kex-config, ssh-old-openssh, ssh-no-pq and connect-failed.

QUIC

The QUIC check (0.2.0): quic-pq-preferred, quic-pq, quic-no-mlkem, quic-hello-rejected, quic-no-reply, quic-version.

Fixes by server

The config lines for each server, and the Tunnel fallback, are on Fixes by server.