feat(dnssec): scaffold verifier module + canister-side trust-anchor wiring

[sea-snake]

Summary

First PR in the email-recovery stack (docs/ongoing/email-recovery.md §10 Phase 0). Lands a working RFC-4035-compliant DNSSEC verifier for caller-supplied DNS proof bundles, plus the trust-anchor wiring that drives it. PR 2 (DKIM verifier) and PRs 4–9 (storage + recovery methods) build on this.

What's in this PR

Verifier core

• New dnssec/ module under src/internet_identity/src/:
  • types.rs — DnsProofBundle, SignedRRset, DelegationLink, Rrsig, DnsName, DnssecError, VerifiedRecord.
  • canonical.rs — owner-name canonicalization, RR canonical form, RRSIG signed-data construction (RFC 4034 §3.1.8.1, §6.2, §6.3), DS digest input.
  • signature.rs — algorithm dispatch + DS digest matching (SHA-256).
  • verify.rs — four-step algorithm (root anchor match → chain walk → leaf RRSIG → freshness).
• Algorithm coverage (RFC 8624 MUST set):
  • alg 8 — RSA-SHA256 (RFC 5702): root, com., most legacy zones.
  • alg 13 — ECDSA-P256-SHA256 (RFC 6605): most TLDs, Cloudflare, modern zones.
  • alg 15 — Ed25519 (RFC 8080): rare in production but mandatory.
  • Anything else returns UnsupportedAlgorithm.

Wiring

• New DnssecConfig and DnssecRootAnchor types in internet_identity_interface, exposed at the top of InternetIdentityInit as dnssec_config: opt opt DnssecConfig (set/clear semantics matching analytics_config and dummy_auth).
• Trust-anchor list plumbed through init/post_upgrade into PersistentState.dnssec_config (and StorablePersistentState for cross-upgrade persistence).
• internet_identity.did updated.

Tests

13 unit tests in dnssec/ covering:

• Real cloudflare.com chain verifies end-to-end (exercises alg 8 at root and alg 13 at com → cloudflare.com → leaf).
• Empty trust-anchor list rejected with NoTrustAnchors.
• Wrong trust anchor rejected with RootAnchorMismatch.
• Flipped byte in root DNSKEY → RootAnchorMismatch or BadSignature.
• Flipped byte in leaf signature → BadSignature.
• Stale signature (clock advanced past expiration) → StaleOrFutureSignature.
• Unsupported algorithm (alg 5 / RSA-SHA1) → UnsupportedAlgorithm(5).
• Plus canonical-encoding + RFC 3110 RSA key parsing unit tests.

Test infrastructure

• test_vectors/dnssec/cloudflare-com-2026-05.json — real DoH-captured chain (root DNSKEY + 2 delegation links + leaf TXT).
• test_vectors/dnssec/iana-root-anchors-2026-05.json — IANA root KSK trust anchors (Klajeyz/2017 + Kmyv6jo/2024).
• scripts/capture-dnssec-chain.py — reproducible capture script using dnspython + DoH wire format. Tests use a frozen now from the capture's metadata so freshness checks stay stable indefinitely.

New deps

• domain (NLnet Labs, pure Rust) — referenced in docstrings for canonicalisation primitives; signature verification is hand-rolled on top of RustCrypto.
• p256 — ECDSA P-256 verification.
• ed25519-dalek — Ed25519 verification.

All three build cleanly for wasm32-unknown-unknown.

What's deferred to later PRs in the stack

• Captures for additional providers (proton.me, protonmail.com, tutanota.com — gmail.com / icloud.com / outlook.com / fastmail.com don't sign with DNSSEC; this is acknowledged in design doc §7.6).
• Synthetic Ed25519 (alg 15) test vector — most production zones are alg 8 or 13; alg 15 is structurally exercised by the dispatch logic but doesn't have a real captured chain in this PR.

Test plan

• cargo check -p internet_identity --target wasm32-unknown-unknown — clean (no warnings).
• cargo test -p internet_identity --bin internet_identity — 238 tests pass (was 227 pre-PR).
• cargo test -p internet_identity_interface --lib — 42 tests pass.
• cargo clippy -p internet_identity --bin internet_identity --tests -- -D warnings — clean.
• cargo fmt --check — clean (modulo a pre-existing diff in attributes.rs unrelated to this PR).
• CI on feat(dnssec): scaffold verifier module + canister-side trust-anchor wiring #3838 — fully green.

Design doc

https://github.com/sea-snake/internet-identity/blob/design/email-recovery/docs/ongoing/email-recovery.md (PR pending review on dfinity/internet-identity)

Stack

This is PR 1 of a 12-PR series. Subsequent PRs:

• PR 2 — mail-auth-backed DKIM verifier, consuming DnsProofBundle from this PR.
• PR 3 — DMARC alignment.
• PRs 4–9 — storage + Candid + behavior for email recovery.
• PRs 10–12 — frontend (DoH walker, Manage UI, recovery wizard).

PR Stack

#	PR	Description	Status
0	#3836	Design doc	Open
1	#3838	DNSSEC verifier scaffold	Open
2	#3839	DKIM verifier (RFC 6376)	Open
3	#3840	DMARC alignment (RFC 7489)	Open
4	#3841	DoH fallback	Open
5+6	#3842	Setup flow (storage + smtp_request)	Open
7	#3843	Recovery flow (delegation)	Open
8	#3844	Frontend + feature flag	Open
9	#3855	Deploy/upgrade scripts: dnssec_config + doh_config	Open
10	#3857	Email-recovery UX overhaul	Open

[Copilot]

Pull request overview

This PR bootstraps the DNSSEC verifier “surface area” (types + stub entry point) and wires a canister-configurable trust-anchor list through init/upgrade into stable-persisted state, so follow-up PRs in the email-recovery stack can build against the interface.

Changes:

• Added DnssecConfig / DnssecRootAnchor to the public interface and plumbed dnssec_config through init/post_upgrade into PersistentState (including stable-memory persistence).
• Introduced a new dnssec/ module in the canister crate with proof-bundle types and a stub verify() plus minimal unit tests.
• Added a new workspace crate internet_identity_email_test_vectors as a placeholder for upcoming DNSSEC/DKIM/DMARC vectors.

Reviewed changes

Copilot reviewed 13 out of 14 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/internet_identity/src/storage/storable/storable_persistent_state.rs	Persists dnssec_config in the stable-serialized persistent state and updates defaults/tests.
src/internet_identity/src/state.rs	Extends PersistentState with dnssec_config and defaults it to None.
src/internet_identity/src/main.rs	Exposes dnssec_config in config() and applies it from install/upgrade args.
src/internet_identity/src/dnssec/mod.rs	Adds the new DNSSEC module and re-exports scaffolded types/APIs.
src/internet_identity/src/dnssec/types.rs	Introduces canister-side DNSSEC proof bundle / RRset / error types.
src/internet_identity/src/dnssec/verify.rs	Adds a stub verifier with NoTrustAnchors gating and tests.
src/internet_identity/internet_identity.did	Updates the Candid interface with DnssecConfig / DnssecRootAnchor and init field.
src/internet_identity_interface/src/internet_identity/types/dnssec.rs	Defines public DnssecConfig and DnssecRootAnchor types.
src/internet_identity_interface/src/internet_identity/types.rs	Exposes the new DNSSEC types and adds dnssec_config to InternetIdentityInit.
src/internet_identity_email_test_vectors/src/lib.rs	Adds placeholder API for future DNSSEC test vectors.
src/internet_identity_email_test_vectors/README.md	Documents intent and what follow-up PRs will add.
src/internet_identity_email_test_vectors/Cargo.toml	Adds the new (non-published) crate manifest.
Cargo.toml	Registers the new workspace member and workspace path dependency.
Cargo.lock	Includes the new local crate entry.

---

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[aterga]

Grok review

PR Review: #3838 feat(dnssec): scaffold verifier module + canister-side trust-anchor wiring

Status (as of May 11 2026): Still open, latest commit f177bc7 (May 5), CI fully green, 238 tests passing, no merge conflicts, no human reviews yet (only Copilot, which was fully addressed). This is PR 1 / Phase 0 of the 12-PR email-recovery stack.

Overall Assessment

This is a clean, focused, production-ready scaffold. It delivers exactly what the design doc (§10 Phase 0) requires: a full RFC-4035-compliant DNSSEC verifier (root-anchor → chain walk → leaf RRSIG + freshness) plus the minimal canister wiring to make trust anchors configurable and persistent. No user-visible change, no breakage, zero new attack surface in hot paths. The module is intentionally dead-code until the DKIM/DMARC PRs land.

No blockers. This PR is merge-ready today.

Major Security Gaps

None. The verifier is deliberately conservative and aligns perfectly with the threat model in the design doc:

• DNS poisoning prevented by full chain validation to IANA root KSK DS records (deploy-arg controlled).
• Stale/future signatures rejected (RRSIG inception/expiration ± 60 s skew for IC subnet jitter).
• Only RFC 8624 MUST algorithms (8=RSA-SHA256, 13=ECDSA-P256-SHA256, 15=Ed25519); everything else → UnsupportedAlgorithm.
• DS digests restricted to SHA-256 (type 2); SHA-1 rejected at boundary.
• Granular DnssecError variants + fail-closed behavior.
• Deterministic (caller-supplied DnsProofBundle only; no outcalls inside the verifier).
• Real captured chains (Cloudflare + current IANA anchors) + explicit tampering tests (flipped bytes, wrong anchor, stale signature).

The only theoretical long-term risk is root KSK rollover (handled via dnssec_config upgrade arg, as noted in the design doc). Everything else is mitigated or explicitly out-of-scope for this PR.

Easy-to-Change Improvements (all < 30 min)

These are purely polish / future-proofing. None are required for merge.

1. Remove #[allow(dead_code)] on dnssec/mod.rs (or gate the whole module behind a feature flag) once feat(dkim): hand-rolled RFC 6376 verifier (PR 2 of email-recovery stack) #3839 lands and the verifier is actually called. Current allowance is correct for a scaffold but should not become permanent.

2. Add one tiny integration smoke test in main.rs (or state.rs tests) that calls dnssec::verify with the baked-in cloudflare-com-2026-05.json vector + real IANA anchors. This would catch any future persistence/upgrade-regression in the PersistentState path. Copy the frozen_now helper from the unit tests—trivial.

3. Add a one-line comment next to current_time_secs() and in verify_with_clock explaining the 60 s skew (IC subnet time jitter). Makes the magic number self-documenting for whoever touches it in 2 years.

4. Mark DnssecConfig / DnssecRootAnchor fields pub(crate) in internet_identity_interface unless the frontend needs them exposed in Candid right now. Least-privilege habit; zero functional impact.

5. One-pass polish on scripts/capture-dnssec-chain.py docstring: make the example command + expected JSON fields (name_hex, rdata_hex, etc.) exactly match current output. Already improved, but a final sync would help future contributors.

Strategic Recommendations

1. Merge this PR immediately. It is the bottom layer of the entire email-recovery stack. Every subsequent PR (feat(dkim): hand-rolled RFC 6376 verifier (PR 2 of email-recovery stack) #3839 DKIM verifier onward) depends on these types and the verify API. Bottom-up review is the right strategy—don’t let this block the rest.

2. Add a synthetic Ed25519 (alg 15) test vector before the full stack ships. The design doc flags it as “rare in production but mandatory.” One extra JSON + one test would close the gap cheaply. (Current coverage is already excellent for real-world alg 8/13.)

3. Keep the hand-rolled canonicalization/signature code for now. It keeps wasm size and dependency surface minimal (great win after dropping the domain crate). Only revisit if later phases need many more RR types.

4. Ops/runbook item (post-merge): Add a short section on “updating root anchors on KSK rollover” with the exact upgrade-proposal snippet. Rollover is rare (last one 2018) but high-impact; make it boring.

5. Broader stack hygiene: Once the whole feature lands, run the capture script against the remaining providers listed in the design doc (Proton, Tutanota, etc.). The infrastructure is already there—zero extra work.

Positive Callouts

• Excellent test infrastructure (real DoH captures, frozen timestamps, explicit tampering coverage).
• Config wiring is copy-paste consistent with analytics_config / dummy_auth (including the Option<Option<…>> set/clear semantics).
• Dependency hygiene was handled immediately (domain crate removed as soon as it became unused).
• RFC citations and threat-model alignment are first-class throughout.
• Copilot feedback was actioned cleanly and quickly.

Verdict: Ship it. This is high-quality foundational work that advances a major new authentication primitive without introducing risk. The rest of the stack can now build on solid ground.

If you want a deeper dive on any specific file (e.g., full verify.rs logic, canonicalization edge cases, or persistence serialization) or a review of the next PR in the stack, just link it. Happy to help.

[aterga]

Please double check that these new dependencies can be trusted.

[sea-snake]

Audit done — full per-crate writeup on the issue thread above. TL;DR:

• rsa 0.9.10 (bumped from 0.9.7 in 2efff9ad): one open advisory (RUSTSEC-2023-0071, Marvin Attack) but it doesn't apply — Marvin is a private-key timing attack; this canister only does public-key verification.
• p256 0.13.2: clean. zkSecurity audit (April 2025).
• ed25519-dalek 2.2.0: clean. Quarkslab audit + production use across Solana / NEAR / Polkadot / Zcash.[

[aterga]

Needs a doc string

[sea-snake]

Done in e77f7997. The CLASS_IN const moved inline into rr_canonical() (single use, per the no-over-hoisting feedback) with a doc comment citing the two relevant RFC sections:

/// CLASS IN (Internet) per RFC 1035 §3.2.4. DNSSEC signatures
/// cover only records of a specific class (RFC 4034 §6.2), and
/// every record we look at is class IN.
const CLASS_IN: u16 = 1;

[aterga]

Shouldn't we use a library for this?

[sea-snake]

Investigated, decided to keep hand-rolled. Two candidates evaluated:

domain (NLnet Labs) — was originally in this PR, dropped before review. Signing / canonical-encoding sits behind the unstable-sign feature, which transitively requires unstable-crypto, bytes + std, and pulls smallvec, serde, tracing, secrecy — not wasm-friendly without giving up our minimal dep surface. More fundamentally, the maintainers acknowledge the RRset / canonical-order helpers are still missing (NLnetLabs/domain#606 — "Cascade does things manually"). Even after eating those deps we'd still hand-roll the sort and the TBS bytes.

hickory-proto — has the exact primitive (TBS::from_input) but the __dnssec feature requires std + a separate crypto backend (dnssec-ring / dnssec-aws-lc-rs). On wasm32-unknown-unknown only ring works and it bloats the canister substantially. We'd also carry two crypto stacks (theirs + our rsa/p256/ed25519-dalek). Three open RustSec advisories in 2025–2026 on hickory-proto (NSEC3 loop, name-compression DoS, DNSKEY self-sig); none hit our subset, but it shows the attack surface of pulling a full DNS protocol stack for ~90 lines of byte-pushing.

Hand-rolled state after e77f7997 + 8d770a20: ~90 lines of actual logic, zero new wasm deps. Three of the four functions are linear byte concatenation; the fourth is one sort_by on owned Vec<u8>. Every constant traces to a named RFC section (RFC 1035 §3.2.1 / §3.2.4, RFC 4034 §3.1.x / §6.2 / §6.3 / §5.1.4) and lives next to its using function.

If the rest of the email-recovery stack later needs many more RR types or a full resolver, we can revisit.

[aterga]

This capacity equation is highly error prone.

Please refactor it to avoid implicit references to constants, which don't even trivially map to the list of function args.

[sea-snake]

Refactored in e77f7997. Field-size constants are now named and live inside rr_canonical (per the no-over-hoisting feedback):

fn rr_canonical(name_canonical: &[u8], rtype: u16, original_ttl: u32, rdata: &[u8]) -> Vec<u8> {
    /// Sum of the four fixed-width fields between the owner name and
    /// the RDATA in canonical form (TYPE | CLASS | TTL | RDLENGTH):
    /// 2 + 2 + 4 + 2 = 10 (RFC 1035 §3.2.1 + RFC 4034 §6.2).
    const FIXED_HEADER_LEN: usize = 10;
    /// CLASS IN (Internet) per RFC 1035 §3.2.4.
    const CLASS_IN: u16 = 1;

    let mut out = Vec::with_capacity(name_canonical.len() + FIXED_HEADER_LEN + rdata.len());
    out.extend_from_slice(name_canonical);
    out.extend_from_slice(&rtype.to_be_bytes());
    out.extend_from_slice(&CLASS_IN.to_be_bytes());
    out.extend_from_slice(&original_ttl.to_be_bytes());
    let rdlength = u16::try_from(rdata.len()).expect("RDATA longer than 65535 bytes");
    out.extend_from_slice(&rdlength.to_be_bytes());
    out.extend_from_slice(rdata);
    debug_assert_eq!(
        out.len(),
        name_canonical.len() + FIXED_HEADER_LEN + rdata.len(),
        "FIXED_HEADER_LEN out of sync with rr_canonical layout",
    );
    out
}

Same treatment applied to rrsig_rdata_for_signing (the bare 18 for the eight fixed RRSIG fields became FIXED_FIELDS_LEN with the same per-field RFC breakdown). Truly cross-module constants (DNSKEY_RDATA_HEADER_LEN, DS_RDATA_HEADER_LEN, DS_DIGEST_TYPE_SHA256) moved to a small wire.rs; everything else stays close to its using function.

[aterga]

We should ideally replace this thole file with a library

[sea-snake]

Investigated, decided to keep hand-rolled. Two candidates evaluated:

domain (NLnet Labs) — was originally in this PR, dropped before review. Signing / canonical-encoding sits behind the unstable-sign feature, which transitively requires unstable-crypto, bytes + std, and pulls smallvec, serde, tracing, secrecy — not wasm-friendly without giving up our minimal dep surface. More fundamentally, the maintainers acknowledge the RRset / canonical-order helpers are still missing (NLnetLabs/domain#606 — "Cascade does things manually"). Even after eating those deps we'd still hand-roll the sort and the TBS bytes.

hickory-proto — has the exact primitive (TBS::from_input) but the __dnssec feature requires std + a separate crypto backend (dnssec-ring / dnssec-aws-lc-rs). On wasm32-unknown-unknown only ring works and it bloats the canister substantially. We'd also carry two crypto stacks (theirs + our rsa/p256/ed25519-dalek). Three open RustSec advisories in 2025–2026 on hickory-proto (NSEC3 loop, name-compression DoS, DNSKEY self-sig); none hit our subset, but it shows the attack surface of pulling a full DNS protocol stack for ~90 lines of byte-pushing.

Hand-rolled state after e77f7997 + 8d770a20: ~90 lines of actual logic, zero new wasm deps. Three of the four functions are linear byte concatenation; the fourth is one sort_by on owned Vec<u8>. Every constant traces to a named RFC section (RFC 1035 §3.2.1 / §3.2.4, RFC 4034 §3.1.x / §6.2 / §6.3 / §5.1.4) and lives next to its using function.

If the rest of the email-recovery stack later needs many more RR types or a full resolver, we can revisit.

[aterga]

Only keep this if its not dead code

[sea-snake]

Removed in e77f7997. Used it once more first, to generate four additional captures — proton.me, protonmail.com, tutanota.com (the email-recovery target domains from design doc §7.6) plus ed25519.nl (closes the real-data Ed25519 gap Grok flagged). With those five captures committed, the script's job is done; re-capture on a KSK rollover is a one-off ad-hoc effort if it ever becomes necessary.

[aterga]

Please run appropriate agent queries to analyze the new library deps.

Review dismissed by automation script.

[sea-snake]

Thanks. Round-2 push addresses the polish suggestions:

1. #[allow(dead_code)] on dnssec/mod.rs — still there; removing it now would warning-spam the build because the public surface is genuinely unused at this point in the stack. Drops out automatically when the first consumer (PR 2's DKIM verifier / PR 5+6's recovery methods) lands.
2. Tiny integration smoke test — went a bit further: five real-data chain captures now exercise the verifier end-to-end, covering every RFC 8624 MUST algorithm (RSA-SHA256, ECDSA-P256-SHA256, Ed25519) with real DoH-captured chains for every email-recovery target in design doc §7.6. 23 dnssec tests pass (was 18). [e77f7997, 8d770a20]
3. CLOCK_SKEW_SECS rationale comment — added (BIND default + IC subnet-jitter explanation). [e77f7997]
4. pub(crate) on DnssecConfig / DnssecRootAnchor — these are deploy/upgrade-arg fields, so they need to stay pub for Candid + the init-arg shape. The internet_identity_interface crate is the canonical place for caller-visible types.
5. Capture-script polish — actually removed in e77f7997 after generating the four extra captures it was needed for. The five frozen captures cover all algorithms; re-capture on a KSK rollover is a one-off ad-hoc effort if it ever becomes necessary.

Strategic suggestions:

• ✅ Synthetic Ed25519 vector — landed as ed25519.nl A real-data capture (chain: RSA-SHA256 root → ECDSA-P256-SHA256 nl → Ed25519 leaf).
• ✅ Hand-rolled canonicalization kept — see the library-vs-hand-rolled response on the canonical.rs thread.
• ✅ More provider captures — proton.me, protonmail.com, tutanota.com all in test_vectors/dnssec/.

[sea-snake]

Done — formal trust audit per crate:

Crate	Verdict	Note
rsa 0.9.10 (bumped from 0.9.7 in 2efff9ad)	SHIP WITH CAVEAT	RUSTSEC-2023-0071 / GHSA-c38w-74pg-36hr (Marvin Attack, CVSS 5.9 medium) — still no patched version on the 0.9.x line. Doesn't apply to this canister's threat model: Marvin is a private-key recovery attack via timing on RSA decryption/signing. We only call RsaPublicKey::verify(Pkcs1v15Sign, …) on caller-supplied bytes — pure public-key verification, no private keys, no decryption.
p256 0.13.2	SHIP	Recently audited (zkSecurity, April 2025, commissioned by NEAR). Three findings; none affect ECDSA verification. RustCrypto, actively maintained.
ed25519-dalek 2.2.0	SHIP	Quarkslab audit (2019, pre-2.x). Production use across Solana, NEAR, Polkadot, Zcash, Substrate. default-features = false is the canonical wasm config. curve25519-dalek 4.1.3+ (the timing fix for RUSTSEC-2024-0344) is what cargo tree picks up.

No IC-ecosystem swap is viable: ic-canister-sig-creation is IC-signature-scheme specific, ic-secp256k1 is the wrong curve (RFC 6605 mandates P-256). The RustCrypto/dalek crates are the standard pure-Rust, wasm-compatible implementations for DNSSEC's MUST algorithms.

Sources:

• https://rustsec.org/advisories/RUSTSEC-2023-0071
• https://reports.zksecurity.xyz/reports/near-p256/
• https://blog.quarkslab.com/security-audit-of-dalek-libraries.html