# Possible Improvements (Go & Python Refimpls)

Suggestions that could make the implementations more robust, spec-strict, or production-friendly. **All items below have been implemented** in both refimpls unless noted.

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## 1. **Spec alignment** ✅

- **ext size/depth (Section 4.2.7)**  
  **Done.** Both refimpls reject when serialized `ect_ext` exceeds 4096 bytes or JSON depth exceeds 5 (`ValidateExt` / `validate_ext`). Used in create and verify.

- **jti / wid format**  
  **Done.** Optional UUID (RFC 9562) validation: `CreateOptions.ValidateUUIDs` / `VerifyOptions.ValidateUUIDs` (Go), `validate_uuids` (Python). Helpers: `ValidUUID` / `valid_uuid`.

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## 2. **API and safety** ✅

- **Payload mutation in Create**  
  **Done.** Documented in both: Create may set Iat, Exp, Sub, Par when zero/nil. **Go:** comment on `Create()`; **Python:** create works on a deep copy so the caller’s payload is not modified.

- **Structured errors (Go)**  
  **Done.** Sentinel errors in `ect/errors.go`: `ErrExpired`, `ErrReplay`, `ErrInvalidSignature` (wrapped), `ErrInvalidTyp`, `ErrPolPolDecisionPair`, etc. Verify and create return these where applicable.

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## 3. **Production / operations** ✅

- **Replay cache**  
  **Done.** Documented: JTICache is in-memory; for multi-instance deployments a shared store (Redis, DB) is required. See refimpl README and go-lang/README “Replay cache (multi-instance)”.

- **Observability**  
  **Done.** **Go:** `VerifyOptions.LogVerify func(jti string, err error)` called after each verify. **Python:** `VerifyOptions.on_verify_attempt(jti, err)` callback.

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## 4. **Small cleanups** ✅

- **Python Ledger docstring**  
  **Done.** “Lookup by task id (jti)”.

- **Python `verify`**  
  **Done.** Documented that `par` may be set to `[]` when missing; `from_claims` already supplies `[]`, so mutation is defensive only.

- **par length**  
  **Done.** **Go:** `CreateOptions.MaxParLength`, `VerifyOptions.MaxParLength`, `DAGConfig.MaxParLength` (0 = no limit; default 100 in DAG). **Python:** `CreateOptions.max_par_length`, `VerifyOptions.max_par_length`, `DAGConfig.max_par_length`.

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## 5. **Nice-to-have** ✅

- **inp_hash / out_hash format**  
  **Done.** Optional check in create and verify: `algorithm:base64url` with algorithm in allowlist (sha-256, sha-384, sha-512). Helpers: `ValidateHashFormat` / `validate_hash_format`.

- **Constant-time comparison**  
  **Done.** **Go:** `crypto/subtle.ConstantTimeCompare` for `typ` in verify. **Python:** `hmac.compare_digest` for `typ`.

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**Summary:** All listed improvements are implemented. For production, also consider: key rotation, WIT integration, and metrics around verify/create latency and error kinds.

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## 6. **draft-01 migration** (PARTIALLY IMPLEMENTED)

The refimpl was built against draft-nennemann-wimse-ect-00. The -01 draft introduced breaking changes:

- **Rename `par` to `pred`**: ✅ **Done.** Struct fields, JSON tags, serialization/deserialization, tests, testdata, READMEs updated in both Go and Python.
- **Remove `pol` and `pol_decision`**: ✅ **Done.** Policy claims removed from core Payload. DAG policy checks now read from `ect_ext`. Tests and demos updated to use ext.
- **Remove `sub`**: ✅ **Done.** Removed from Payload struct (Go) and dataclass (Python). Create no longer defaults sub=iss.
- **Update `typ` default**: ✅ **Done.** `exec+jwt` is now preferred; `wimse-exec+jwt` accepted for backward compat. Verify checks both (constant-time).
- **Update `MaxParLength` naming**: ✅ **Done.** Renamed to `MaxPredLength` / `max_pred_length` everywhere.
- **Add L1 support**: The -01 draft introduces unsigned JSON ECTs (Level 1). The refimpl currently only supports L2 (signed JWS).
- **Add L3 support**: The -01 draft introduces audit ledger requirements for Level 3. The existing in-memory ledger needs hash chain and receipt support.
- **Update hash format**: The -01 draft specifies SHA-256 base64url without algorithm prefix (no `sha-256:` prefix), consistent with RFC 9449.