Post-Quantum Cryptography (PQC) TLS readiness: network health, operator, and relay visibility

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Context

Alexander Færøy (ahf) posted a call to action on tor-relays asking operators to upgrade their systems to support post-quantum cryptography in Tor's TLS layer:

Mailing list thread: https://lists.torproject.org/mailman3/hyperkitty/list/tor-relays@lists.torproject.org/thread/MYP2MQDFTJUODF7SJNLJRWLXJK3KTUEU/

Background

• OpenSSL 3.5.0 (released 2025) enabled ML-KEM-768 hybrid key exchange support
• Tor ≥0.4.8.17 supports the x25519/ML-KEM-768 hybrid TLS handshake
• Tor Browser has supported PQC TLS since version 13.5.22 (September 2025)
• As of February 2026, only ~32% of relays (2,969 / 9,185) support X25519MLKEM768
• 5 of the Directory Authorities support it
• Scan results published at https://ahf.me/tor-tls-pqc/2026-02-26/ via the Margot scanner tool

This is a critical network-wide upgrade. Allium can help by surfacing PQC readiness data to make it easy for operators to see where they stand and what needs attention.

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Proposed Changes

1. Network Health Dashboard — new PQC Readiness card

Add a card to network-health.html (alongside the existing Version Compliance card) showing network-wide PQC adoption:

• Primary metric: % of relays supporting X25519MLKEM768
• Relay count: PQC-ready vs not ready (with/without Guard, Exit, Authority breakdown)
• Bandwidth-weighted PQC coverage (what fraction of network capacity is PQC-ready)
• Directory Authority PQC support count (e.g., "5/9 DAs support PQC")
• Trend context if historical scan data is available
• Link to the upstream scan results and mailing list thread for operator guidance

2. Relay Operator (Contact) Pages — PQC summary bullet

On each operator/contact page, add a PQC readiness summary:

• X of Y relays PQC-ready (count and percentage for this operator)
• Bandwidth-weighted PQC coverage for this operator's relays
• Which relays are missing PQC support (linking to their relay pages)
• Suggested action if any relays are not PQC-ready (upgrade OpenSSL to ≥3.5.0 or LibreSSL equivalent)

This gives operators a single place to see their fleet's PQC status.

3. Relay Detail Pages — PQC status indicator

On each individual relay page (likely in the Software and Version section, #software):

• PQC TLS status: Supported / Not Supported / Unknown (unreachable during scan)
• Negotiated key exchange group (e.g., X25519MLKEM768, X25519, secp256r1)
• Negotiated cipher suite (e.g., TLS13_AES_256_GCM_SHA384)
• Scan date (when this relay was last checked)
• If not supported: actionable guidance — "Upgrade to OpenSSL ≥3.5.0 or compatible LibreSSL"

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Data Source

The PQC scan data comes from the Margot scanner tool maintained by the Tor Network Health Team:

• Published at https://ahf.me/tor-tls-pqc/<date>/
• Contains per-relay results keyed by fingerprint: cipher suite, key exchange group, reachability
• Scans run semi-regularly; missing entries indicate unreachable relays (not necessarily lack of support)
• This is not currently in the Onionoo API — would need to be fetched as a separate data source

Data integration considerations

• Add a new API worker (similar to the existing uptime/bandwidth/exit-dns workers) to fetch and parse PQC scan results
• Cache/store results alongside relay data, keyed by fingerprint
• Handle missing relays gracefully (unreachable ≠ unsupported)
• Consider what format the Margot data is published in (HTML table? JSON? CSV?) and parse accordingly
• If the data format or URL structure changes, the integration should be easy to update
• Fall back gracefully if the PQC data source is unavailable

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Open Questions

• Is the Margot scan data available in a machine-readable format (JSON/CSV), or only as an HTML table?
• How frequently are scans published? Can we rely on a stable URL pattern?
• Should we request that this data be added to the Onionoo API for easier integration?
• What is the best heuristic to infer PQC support from Tor version alone (≥0.4.8.17 + OpenSSL ≥3.5.0) as a fallback when scan data is unavailable?

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References

• Mailing list thread: https://lists.torproject.org/mailman3/hyperkitty/list/tor-relays@lists.torproject.org/thread/MYP2MQDFTJUODF7SJNLJRWLXJK3KTUEU/
• PQC scan results: https://ahf.me/tor-tls-pqc/2026-02-26/
• OpenSSL 3.5.0 ML-KEM feature: https://openssl-foundation.org/post/2025-04-29-ml-kem
• Tor 0.4.8.18 / 0.4.9.3-alpha release: https://lists.torproject.org/mailman3/hyperkitty/list/tor-announce@lists.torproject.org/thread/GF6BTDSIL4CGTGQRWFPUJNRZZCLDZ3W3/