feat: govern legacy archive encryption

src/govoplan_campaign/backend/services/zip_service.py

@@ -2,6 +2,8 @@ from __future__ import annotations
 
 import binascii
 from datetime import datetime
+import hashlib
+from importlib import metadata
 import secrets
 import stat
 import struct
@@ -49,6 +51,8 @@ def create_zip_archive(
     output_path.parent.mkdir(parents=True, exist_ok=True)
     members = _normalized_members(files)
     if password:
+        if method not in {ZIP_METHOD_AES, ZIP_METHOD_STANDARD}:
+            raise ValueError(f"Unsupported password-encryption method: {method}")
         if method == ZIP_METHOD_STANDARD:
             _create_zipcrypto_archive(output_path, members, password)
             return output_path
@@ -61,6 +65,51 @@ def create_zip_archive(
     return output_path
 
 
+def zip_archive_evidence(
+    output_path: Path,
+    members: Iterable[Path | ArchiveMember],
+    *,
+    password_protected: bool,
+    method: str,
+) -> dict[str, object]:
+    """Return password-free, content-addressed evidence for one built archive."""
+
+    normalized = _normalized_members(members)
+    archive_bytes = output_path.read_bytes()
+    if password_protected and method == ZIP_METHOD_AES:
+        try:
+            implementation_version = metadata.version("pyzipper")
+        except metadata.PackageNotFoundError:  # pragma: no cover - guarded by writer
+            implementation_version = "unknown"
+        implementation = "pyzipper"
+        archive_format = "WinZip AES"
+    elif password_protected and method == ZIP_METHOD_STANDARD:
+        implementation = "govoplan-campaign.zipcrypto"
+        implementation_version = "1"
+        archive_format = "Legacy ZipCrypto"
+    else:
+        implementation = "python.zipfile"
+        implementation_version = "stdlib"
+        archive_format = "ZIP (unencrypted)"
+    return {
+        "format": archive_format,
+        "method": method if password_protected else "none",
+        "password_protected": password_protected,
+        "implementation": implementation,
+        "implementation_version": implementation_version,
+        "archive_sha256": hashlib.sha256(archive_bytes).hexdigest(),
+        "archive_size_bytes": len(archive_bytes),
+        "members": [
+            {
+                "name": archive_name,
+                "sha256": hashlib.sha256(path.read_bytes()).hexdigest(),
+                "size_bytes": path.stat().st_size,
+            }
+            for path, archive_name in normalized
+        ],
+    }
+
+
 def create_encrypted_zip(output_path: Path, files: list[Path], password: str, method: str = ZIP_METHOD_AES) -> Path:
     """Backward-compatible wrapper for the original per-rule ZIP helper."""