# Zastava Kit (offline bundle)

## Contents
- Schemas + DSSE: `schemas/observer_event.schema.json(.dsse)`, `schemas/webhook_admission.schema.json(.dsse)`.
- Examples: `schemas/examples/*.json` (canonicalised, hashed).
- Thresholds + DSSE: `thresholds.yaml(.dsse)`.
- Exports + DSSE: `exports/observer_events.ndjson(.dsse)`, `exports/webhook_admissions.ndjson(.dsse)`.
- Verification assets: `SHA256SUMS`, `kit/verify.sh`, `kit/ed25519.pub`, `schemas/README.md`, `evidence/README.md`.

## Build (deterministic)
From `docs/modules/zastava`:

```bash
tar --mtime @0 --owner 0 --group 0 --numeric-owner --sort=name \
  -cf - \
  SHA256SUMS schemas exports thresholds.yaml thresholds.yaml.dsse \
  schemas/examples schemas/README.md \
  schemas/observer_event.schema.json schemas/observer_event.schema.json.dsse \
  schemas/webhook_admission.schema.json schemas/webhook_admission.schema.json.dsse \
  exports/observer_events.ndjson exports/observer_events.ndjson.dsse \
  exports/webhook_admissions.ndjson exports/webhook_admissions.ndjson.dsse \
  evidence/README.md kit/README.md kit/verify.sh kit/ed25519.pub \
| zstd -19 --long=27 --no-progress > kit/zastava-kit.tzst
```

Sign the kit itself with the same Ed25519 key (base64url pub: `mpIEbYRL1q5yhN6wBRvkZ_0xXz3QUJPueJJ8sn__GGc`):

```bash
python - <<'PY'
from pathlib import Path
from base64 import urlsafe_b64encode
import json
from cryptography.hazmat.primitives.asymmetric import ed25519
from cryptography.hazmat.primitives import serialization

priv = serialization.load_pem_private_key(Path('/tmp/zastava-ed25519.key').read_bytes(), password=None)
pub = priv.public_key().public_bytes(encoding=serialization.Encoding.Raw, format=serialization.PublicFormat.Raw)
keyid = urlsafe_b64encode(pub).decode().rstrip('=')
pt = 'application/vnd.stellaops.zastava.kit+tzst;version=1'
payload = Path('kit/zastava-kit.tzst').read_bytes()
pae = b' '.join([b'DSSEv1', str(len(pt)).encode(), pt.encode(), str(len(payload)).encode(), payload])
sig = priv.sign(pae)
env = {
    'payloadType': pt,
    'payload': urlsafe_b64encode(payload).decode().rstrip('='),
    'signatures': [{'keyid': keyid, 'sig': urlsafe_b64encode(sig).decode().rstrip('=')}],
}
Path('kit/zastava-kit.tzst.dsse').write_text(json.dumps(env, indent=2, sort_keys=True) + '\n')
print('wrote kit/zastava-kit.tzst.dsse with keyid', keyid)
PY
```

## Verify
1) Verify the kit DSSE before unpacking (optional but recommended) using the public key shipped alongside the kit (run from `docs/modules/zastava`):
```bash
cd docs/modules/zastava
python - <<'PY'
import base64, json, sys
from pathlib import Path
from cryptography.hazmat.primitives.asymmetric import ed25519

root = Path('.')
pub = base64.urlsafe_b64decode((root / 'kit' / 'ed25519.pub').read_text().strip() + '==')
env = json.loads((root / 'kit' / 'zastava-kit.tzst.dsse').read_text())
payload = (root / 'kit' / 'zastava-kit.tzst').read_bytes()
pt = env['payloadType'].encode()
pae = b' '.join([b'DSSEv1', str(len(pt)).encode(), pt, str(len(payload)).encode(), payload])
sig = base64.urlsafe_b64decode(env['signatures'][0]['sig'] + '==')
ed25519.Ed25519PublicKey.from_public_bytes(pub).verify(sig, pae)
decoded_payload = base64.urlsafe_b64decode(env['payload'] + '==')
assert decoded_payload == payload
print('OK: kit DSSE verified')
PY
```
2) Extract and run offline validation of the inner artefacts:
```bash
zstd -d kit/zastava-kit.tzst -c | tar -xf -
./kit/verify.sh
```

## Notes
- Private signing key is held offline; only the public key is shipped.
- All files are deterministic (mtime=0, numeric owners) to keep hashes stable for Evidence Locker ingestion.