# ENC/FER1-RECEIPT/1 — Canonical Encoding for FER/1 Receipts

Status: Draft
Owner: Architecture
Version: 0.1.0
SoT: Yes
Last Updated: 2025-12-01
Linked Phase Pack: PH07
Tags: [evidence, receipt, deterministic, execution]

**Document ID:** `ENC/FER1-RECEIPT/1`
**Profile ID:** `FER_ENC_RECEIPT_V1 = 0x0301`
**TypeTag:** `TYPE_TAG_FER1_RECEIPT_1 = 0x00000301`

**Depends on (normative):**

* `ASL/1-CORE v0.4.x` — value model (`Artifact`, `Reference`, `OctetString`)
* `ENC/ASL1-CORE v1.0.x` — canonical encoding for `Reference`
* `FER/1` — receipt semantics and required fields

---

## 0. Overview

`ENC/FER1-RECEIPT/1` defines the canonical binary encoding for FER/1 receipts.
Receipts are stored as ASL/1 Artifacts with:

```
Artifact.type_tag = TYPE_TAG_FER1_RECEIPT_1
Artifact.bytes    = ReceiptBytes
```

This encoding is deterministic and injective. Ordering is fixed and list
ordering is required for canonicalization.

---

## 1. ReceiptBytes Layout (v1)

All integers are **big-endian**. Lengths are unsigned.

```
ReceiptBytes =
  fer1_version         : U16
  function_ref         : EncodedRef
  input_manifest_ref   : EncodedRef
  environment_ref      : EncodedRef
  evaluator_id_len     : U32
  evaluator_id_bytes   : BYTES
  output_ref           : EncodedRef
  executor_count       : U32
  executor_refs        : EncodedRef[executor_count]
  parity_count         : U32
  parity_entries       : ParityEntry[parity_count]
  started_at           : U64
  completed_at         : U64
```

Rules (normative):

* `fer1_version` MUST be `0x0001`.
* `parity_count` MUST equal `executor_count`.
* Every `ParityEntry.output_ref` MUST equal the top-level `output_ref`.
* `parity_entries[i].executor_ref` MUST equal `executor_refs[i]`.
* `started_at` MUST be less than or equal to `completed_at`.
* `executor_refs` and `parity_entries` MUST be ordered by ascending
  `EncodedRef` byte order to ensure canonicalization.

---

## 2. EncodedRef

`EncodedRef` embeds an ASL/1 `Reference` using a length prefix:

```
EncodedRef =
  ref_len   : U32
  ref_bytes : BYTES   // ReferenceBytes (ENC/ASL1-CORE v1)
```

`ref_len` is the length of `ReferenceBytes`. `ReferenceBytes` uses the
canonical encoding from `ENC/ASL1-CORE v1`.

---

## 3. ParityEntry

```
ParityEntry =
  executor_ref      : EncodedRef
  output_ref        : EncodedRef
  has_sbom_ref      : U8
  sbom_ref?         : EncodedRef  // if has_sbom_ref == 1
  parity_digest_len : U32
  parity_digest     : BYTES
```

`parity_digest` is an opaque, executor-specific digest. Empty digests are
allowed (`parity_digest_len = 0`).

---

## 4. Canonicalization and Validation

Implementations MUST:

* enforce list ordering for `executor_refs` and `parity_entries`,
* reject truncated payloads or trailing bytes, and
* reject any receipt where required references are malformed or invalid.

No other metadata or policy is embedded in the receipt bytes.