by pepdar | 2026-02-19 12:26:02+00:00
I'm one of the draft authors. Several questions here touch real design tradeoffs — addressing the main threads:

Why account URI instead of a public key in the record? (micw, 9dev, csense)

Three reasons:

1. Key rotation without DNS changes. dns-persist-01 exists because DNS updates are expensive. Embedding a public key forces a DNS update on every key rotation — the exact problem this method solves. The account URI survives key rotation (RFC 8555 §7.3.5).

2. CAA alignment. The accounturi parameter matches CAA record syntax (RFC 8657 §3). Domain owners use the same identifier in validation and policy records.

3. Simplicity. Matching uses simple string comparison — no key encoding, no signature verification, no algorithm negotiation. The cryptographic binding between account URI and key pair happens inside ACME, where it belongs.

"Exposing account numbers" / privacy (csense, mmh0000, bflesch)

The account URI is opaque — a URL containing a database key, like https://acme-v02.api.letsencrypt.org/acme/acct/123456789. No email, no name. The privacy exposure is modest: it reveals which CA account controls the domain, similar to what CT logs already show about CA-domain relationships, but with explicit account-level grouping. If you want isolation between domains, use separate accounts.

The accounturi binds validation to a specific account so a stolen DNS record can't be used by a different subscriber. An open PR (#35) adds accounturi to the challenge object so clients can verify it before provisioning.

10-day reuse limit (agwa)

The 10-day maximum comes from the CA/Browser Forum ballot (SC-088), not the IETF draft. The draft defers reuse period to CA policy and caps it at the DNS TTL (see "Validation Data Reuse and TTL Handling" in the Security Considerations). Let's Encrypt is migrating to 7 hours. The TTL cap lets domain owners enforce shorter windows directly.

Mandatory DNSSEC (rmoriz)

Requiring DNSSEC would exclude most domains and block adoption. The current draft specifies DNSSEC validation as SHOULD. An open PR (#35) tightens this: if a CA performs DNSSEC validation and it fails — expired signatures, broken chain of trust — the CA MUST reject the record. This is stricter than general ACME guidance because dns-persist-01 records are long-lived. MPIC (multi-perspective validation) provides the primary defense against on-path attacks regardless of DNSSEC.

Unencrypted DNS queries (1vuio0pswjnm7)

Yes, standard DNS queries are unencrypted. The threat model relies on MPIC — querying from multiple vantage points — not transport encryption. DNSSEC adds an integrity layer where available.

CAA interaction (Ayesh)

Yes. A CAA record with validationmethods=dns-persist-01 combined with accounturi restricts who can validate using this method.

Name-constrained intermediate CAs (infogulch)

Separate problem. dns-persist-01 reduces operational cost of leaf cert issuance by eliminating per-issuance DNS interaction. Delegated intermediates shift the trust model. Both could coexist.

Draft: <https://github.com/ietf-wg-acme/draft-ietf-acme-dns-persist> (PR #35 is an open pull request on the draft with several of the improvements mentioned above.)