# ASL/POLICY-HASH/1 -- Policy Hash Specification

Status: Draft
Owner: Architecture
Version: 0.1.0
SoT: No
Last Updated: 2025-01-17
Tags: [policy, hash, federation, trust]

**Document ID:** `ASL/POLICY-HASH/1`
**Layer:** L2 -- Policy binding semantics (no encoding)

**Depends on (normative):**

* `ASL/FEDERATION/1`

**Informative references:**

* `ASL/DAM/1` -- Domain Authority Manifest
* `ASL/DAP/1` -- Domain admission

---

## 0. Conventions

The key words **MUST**, **MUST NOT**, **REQUIRED**, **SHOULD**, and **MAY** are to be interpreted as in RFC 2119.

ASL/POLICY-HASH/1 defines the logical structure and hashing rules for policy documents. It does not define transport or storage encodings.

---

## 1. Purpose

The policy hash binds domain rules to snapshots, authority, and federation decisions without embedding mutable policy text into artifacts.

---

## 2. Policy Coverage (Normative)

The policy hash MUST cover semantic constraints that affect correctness or trust:

1. Publication rules
2. Execution rules
3. Federation rules
4. Retention and GC constraints
5. Visibility rules

---

## 3. Logical Structure

```text
DomainPolicy {
    version            : u32
    publication_policy : PublicationPolicy
    execution_policy   : ExecutionPolicy
    federation_policy  : FederationPolicy
    retention_policy   : RetentionPolicy
    visibility_policy  : VisibilityPolicy
    reserved0          : u32
}
```

Section schemas (minimal):

```text
PublicationPolicy {
    require_signature   : bool
    allowed_roles[]     : Role
    snapshot_required   : bool
}

ExecutionPolicy {
    per_signature_required : bool
    allowed_roles[]        : Role
    deterministic_only     : bool
}

FederationPolicy {
    export_published_only : bool
    require_snapshot      : bool
    trusted_domains[]     : DomainID
}

RetentionPolicy {
    gc_unpublished_allowed : bool
    min_snapshot_retention : u32
}

VisibilityPolicy {
    internal_hidden     : bool
    published_read_only : bool
}
```

---

## 4. Defaults and Validation (Normative)

All fields MUST be present. Defaults apply only to explicit values:

* `allowed_roles[]` MAY be empty (no roles allowed)
* `trusted_domains[]` MAY be empty (no domains trusted)
* `min_snapshot_retention` MAY be 0 (no minimum)
* `reserved0` MUST be 0

A policy is invalid if any boolean is outside {0,1} or if `version` is unsupported.

---

## 5. Canonicalization Rules (Normative)

The policy hash MUST be computed from canonical bytes:

1. Field order fixed
2. Arrays sorted lexicographically
3. No whitespace or comments
4. Integers encoded big-endian
5. Booleans encoded as 0x00 or 0x01
6. No optional fields omitted; defaults must be explicit

---

## 6. Hash Computation

```
policy_bytes = CanonicalSerialize(DomainPolicy)
policy_hash  = HASH(policy_bytes)
```

The hash algorithm is SHA-256 unless explicitly overridden by domain policy.

---

## 7. Storage Locations

The policy hash SHOULD be stored in:

* Domain Authority Manifest (DAM)
* Snapshot metadata
* Federation metadata
* Optional PER metadata

---

## 8. Policy Evolution

Policy changes MUST NOT mutate history. A new policy requires:

1. New policy document
2. New policy hash
3. New DAM
4. New snapshots referencing the new hash

---

## 9. Summary

ASL/POLICY-HASH/1 defines a minimal, deterministic policy hash that binds domain rules to authority and snapshots without embedding mutable policy text into artifacts.