msquic — Post-quantum certificate chain, compressed per RFC 8879

Inconclusive

The run did not exercise this test: the client's signature_algorithms named nothing that can verify an ML-DSA-87 chain, so this endpoint refused before sending one. Post-quantum certificates are not reachable for this client at all, which is a fact about it rather than a gap in the run.

The run did not establish what this client does here — either it was never put in the situation, or its answer admits more than one reading. Not a failure, and never counted as one.

What was measured

Client

msquic — .NET HttpClient + msquic, 2.7.0

Test

Post-quantum certificate chain, compressed per RFC 8879 — t-cert-compression-pq

Clause

RFC 8879 §4, RFC 8446 §4.4.2 (MAY)

Class

discretionary — The RFC permits either behaviour; the report says which was chosen.

Required behaviour

Decompress and parse a 55 KB ML-DSA-87 chain, then judge it on its merits. Nothing here is graded: RFC 8879 is optional, no RFC requires support for ML-DSA certificates, and §4 expressly lets a receiver cap the decompressed size and abort. What the port reports is which of those a client does. The chain is deliberately issued by a private CA nobody trusts, and that is what makes the measurement work rather than spoiling it. A client that rejects it for its *trust anchor* — unknown_ca, or bad_certificate — has already decompressed a 55 KB certificate message, parsed ML-DSA-87 structures it may never have seen and got as far as chain building. That is the whole capability under test, and the rejection that follows is correct behaviour, not a failure. A client that cannot get that far answers differently: decode_error or a record-size abort says the compressed chain itself defeated it, which is the outcome the post-quantum migration needs to know about. Certificate sizes are the half of that migration nobody can configure their way out of — ML-DSA-87 signatures are 4,627 bytes each and every chain carries several.

Measured

2026-09-18

Reproduce it

The suite is the judge, so the reproduction is to point the same client at the same test and let the server report what it saw.

SESSION=$(curl -sX POST https://conformance.pqcrypta.com/session | jq -r .id)
# then drive msquic at the test URL and read the verdict:
curl -s https://conformance.pqcrypta.com/report/$SESSION.json | jq '.results["t-cert-compression-pq"]'