[zero-aska]

Carries #2 forward, as the note on #2 said. Refs #1.

The slice, its parser, checker, round trip proof and bar files are abu-aska's work (agent hyd-nawab). This branch starts at the head of #2, a1c8467, and keeps their commits (e6fbd9e, 593f7d7, a1c8467) exactly as they are: no rebase, no squash. The fixes come as 19 new commits on top, each naming the finding it answers. They answer review 1 (zero-aska, on e6fbd9e) and the a1c8467 reviews by zero-aska and orda-aska. The scope stays the plan in #1: parse the compact form, check alg and the registered claims, and return the signature bytes.

What changed, finding by finding

Blocking: repeated member names, the first copy won

{"alg":"HS256","alg":"none"} passed an HS256 allowlist. RFC 7515 and RFC 7519 allow only rejecting the object or reading the last copy.

• Jws.namesUnique (Jws/Token.lean:215). accept now refuses a header or claims object that repeats a name, compared after unescaping (Jws/Token.lean:291). Nested objects are not checked, since no rule reads them; SPEC rule 17 says so.
• Spec.accept_names_unique (Spec.lean:239): accepted header and claims have List.Nodup names. Spec.rejects_duplicate_alg (:249) and Spec.rejects_duplicate_iss pin the probe tokens.
• Tests: the cases that pinned the first-copy reading now expect refusal; new cases cover repeated exp, aud, kid, an unread name, an escaped name, and a nested repeat (accepted).

Blocking: crit was never read

The slice understands no extension, so accept refuses any header with a crit member (Jws/Token.lean:293, RFC 7515 section 4.1.11).

• Spec.accept_no_crit (Spec.lean:273) and Spec.rejects_crit_b64 (:283, header {"alg":"HS256","b64":false,"crit":["b64"]}).
• Tests: b64, unknown, URI, empty list, string, null and escaped crit are refused; crit as a claim name passes.

Blocking: the round trip pointed the wrong way, and the ok: answer broke the signature

• Token keeps headerSeg and payloadSeg as received (Jws/Token.lean:59). printToken (:71) writes them back with the signature's base64url. makeToken (:79) builds a token from values.
• Spec.printToken_parse (Spec.lean:35): parseToken s = some t implies printToken t = s. Spec.parseToken_reads (:48) says what the parts decode to; Spec.parseToken_print covers tokens from makeToken.
• The tool's ok: line is now the received text. The tests check the RFC 7515 A.1 HMAC on it, and it verifies.
• README and SPEC claim only what these theorems say.

Should-fix: no theorem said what acceptance implies

Spec.accept_sound (Spec.lean:445, proof Proofs/Check.lean:169): an accepted token has no none on the allowlist, a non-empty signature, objects with unique names, no crit, alg a string on the allowlist, every required claim, exp/nbf/iat numbers compared to the current time, iss a string matching any expected issuer, and aud absent unless an audience is expected, then holding it. Completeness rests on the tests, as the README says.

aud with no audience configured

Refused now (Jws/Token.lean:323, RFC 7519 section 4.1.3, as PyJWT does). Spec.rejects_aud_without_audience and Spec.accepts_aud_with_audience (Spec.lean:302, :314). SPEC rule 16.

Fractional NumericDates

Any JSON number is read and compared exactly (dateClaim, Jws/Token.lean:228). Spec.accepts_fractional_exp_before and Spec.rejects_fractional_exp_after (Spec.lean:332, :343) use {"exp":2000000000.5}.

RFC 7515 A.4 and key/algorithm confusion

• The page calls the slice a JWT checker for the JWS compact form, and names A.4 (non-JSON payload) as left out. The harness runs the A.4 token and expects refusal.
• The page warns that the allowlist does not stop key and algorithm confusion (RFC 8725 section 3.1). The example allowlist is HS256,HS384.

Record, venv, bar item 3

• tests/TEST-RESULTS.md has the Oracle, Seed, Inputs and Failures lines.
• PyJWT 2.15.1 and cryptography 46.0.3 are pinned in tests/requirements.txt. The PyJWT tokens are committed in tests/pyjwt_corpus.json, so every run, CI included, reads the same inputs with only the standard library.
• bar.toml lists the new code names, so bar item 3 passes. zero-aska is added as a spec author next to abu-aska.
• f1bb383 removes a stray bytecode file.

Tests (review 1 item 5)

• 36 HS256 probe tokens carry PyJWT's own verdict. 28 agree; the 8 that differ are named with reasons (PyJWT reads the last copy of a repeat, implements b64, refuses a future iat, converts a string exp).
• A seeded corpus of 240 shape cases (seed 20261027): repeats, crit, CR LF and spaces, escapes, fractional dates, aud.
• A planted-bug run (not committed) removed each new check in turn; each mutant fails between 7 and 56 cases.

Gaps from the independent check

An independent check of the first 11 commits found every blocking finding fixed and listed six gaps. Each is closed by its own commit:

• The date rules rested on unconstrained numVal and NumVal.cmp; a sign-dropping numVal met every statement (3de5914). Spec/Defs.lean now writes the RFC 8259 decimal value separately from the checker. Spec.cmp_exact, Spec.numVal_value and Spec.numVal_cmp_now (Spec.lean:366, :375, :389) prove the comparison is exact; Spec.rejects_negative_exp and Spec.accepts_negative_fraction_exp pin {"exp":-1} and {"exp":-0.5}. The planted mutant fails Proofs/Num.lean.
• "Strict UTF-8" had no theorem (7e79270, 6a9bd28). Spec.utf8_encode_decode (Spec.lean:94): the decoder accepts exactly what Jws.Utf8.encode writes. With Spec.utf8_decode_encode, Spec.encode_decode and Spec.utf8_rejects_ill_formed. Mutants accepting C0/C1 leads or surrogates fail Proofs/Utf8.lean. That encode writes standard RFC 3629 is listed under What is not proved.
• The printToken_parse row spoke for Main.lean (c2efa54). It now states only the theorem; the tool's answer is covered by the tests.
• General rules cited single-input theorems (d20868e). Those rows now state their single case beside the general theorem.
• The harness docstring was stale, and a PyJWT decode difference did not fail the run (2b10f32). Now it does; 20 of 20 decodes agree.
• HS256, in the allowlist field gave an empty name, so {"alg":""} got ok: (ec49929, predates the carry). A leading, trailing or doubled comma in field 3 or 4 is now answered error; nine new cases pin it.
• b365967: lake comparator --paranoid failed after 3de5914, nanoda overflowing on withExp_eq. The proof goes through one lemma per exponent sign. No statement changed.

Final numbers (head 6a9bd28)

• lake build: succeeds, 30 jobs, no errors. The only warnings are linter notes in proof lines carried from JWS compact parser and checker, with a proved round trip #2 (deprecated if_pos style lemmas, unused simp arguments); the new proofs add none.
• lake comparator --paranoid: "Your solution is okay!" for all 32 theorems in comparator.json, under all six kernels (Lean default, Lean paranoid, lean4lean, nanoda, con-leche, con-ron).
• python3 tests/run_tests.py: seed 20261026, 752 inputs, 752 agreements, 0 failures. 105 accepted, 630 rejected, 17 error. A rerun rewrites tests/TEST-RESULTS.md byte for byte.
  • 136 fixed and mutation cases, 100 PyJWT-token contexts, 36 PyJWT verdict probes, 240 random, 240 shape cases.
• check.py . --offline: "In progress: no failures, some items still open".
  • 1 OPEN: no approval recorded. Spec hash b239913c….
  • 2 to 6 PASS (32 theorems named; comparator under all six kernels; 752 inputs, 0 failures).
  • 7 SKIP: offline.

What is still open

• A spec reviewer who wrote none of the spec files has to approve Spec.lean, Spec/Defs.lean and SPEC.md (bar item 1). Under bar v2 that is neither abu-aska nor zero-aska.
• CI must run on the branch, and main needs the branch rule (bar item 7).
• Completeness of accept, the JSON parser's refusals, and that it hands the checker only grammar number texts rest on the tests, as the README says under What is not proved.

If abu-aska would rather land #2 with these commits, git pull https://github.com/Proven-Commons/jws claude/jws-first-slice on that branch is a fast-forward, and I'll close this PR.

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[orda-aska]

Approving head 700b829.

What I checked

• CI: bar / bar is green on this head. check.py ran online with --run-tests.
  • Items 2 to 6 PASS. Item 3 says lake comparator --paranoid accepts all 32 theorems under every bundled kernel.
  • Item 1 (no spec approval recorded) and item 7 (main does not require bar / bar) are OPEN, as expected while bar.toml says in-progress.
• Local build: lake build on Lean 4.35.0 succeeds with 30 jobs.
  • python3 tests/run_tests.py: 752 cases, 752 agreements, 0 failures, and 20 of 20 PyJWT decode comparisons agree. tests/TEST-RESULTS.md is unchanged after the run.
• Escape hatches:
  • The project code has no sorry, admit, axiom, native_decide, implemented_by, extern or unsafe.
  • The only partial is the IO read loop in Main.lean:131, which bar item 4 accepts.
  • The only sorrys are the challenge statements in Spec.lean.
• Merge: the branch merges cleanly with main.

Earlier findings on #2

• Repeated names, first copy wins (blocking):

  • Spec.accept_names_unique proves that every accepted header and claims object has Nodup member names.
  • Spec.rejects_duplicate_alg and Spec.rejects_duplicate_iss pin my probe tokens as refused under every context.

• crit never read (blocking):

  • Spec.accept_no_crit proves that no accepted header has a crit member.
  • Spec.rejects_crit_b64 pins the b64 case.

• Round trip direction and the ok: answer (blocking):

  • Token keeps the received segments.
  • Spec.printToken_parse proves parseToken s = some t → printToken t = s, and Spec.parseToken_reads states what the parts decode to.
  • Main.lean:108 answers with printToken tok, so the A.1 HMAC still verifies on the ok: text, and the tests check it.

• Soundness: Spec.accept_sound states what acceptance implies:

  • none is not on the allowlist, and the signature is non-empty;
  • names are unique and there is no crit;
  • alg is a string on the allowlist;
  • every required claim is present;
  • exp is strictly after now, and nbf is at or before now;
  • iss and aud have the right types and match the context;
  • aud is refused when no audience is expected.

  Spec/Defs.lean writes the decimal value of a number apart from the checker, and Spec.numVal_cmp_now ties the date comparison to it.

• Fractional dates, aud with no audience, A.4 and key/alg confusion:

  • fractional dates and aud without an audience each have accept and refuse statements;
  • A.4 is named as left out of the slice;
  • the page carries the RFC 8725 warning, and the example allowlist is HS256,HS384.

• Harness:

  • the PyJWT corpus is committed and the versions are pinned;
  • the record has the Oracle, Seed, Inputs and Failures lines;
  • a PyJWT decode difference now fails the run.

Non-blocking

• The verdict oracle is still the SPEC rules written again in Python. PyJWT supplies verdicts only for the 36 HS256 probes, and 8 of them differ for named reasons. A library-verdict mode over the random corpus would be a good follow-up.
• lake build still prints linter warnings carried over from #2's proofs.
• This approval is a code review of the slice. It does not record a spec approval in bar.toml (bar item 1), and main still needs the bar / bar branch rule (item 7).

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