> For the complete documentation index, see [llms.txt](https://docs.telys.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.telys.ai/security/trust-anchors.md).

# Trust anchors

Telys will not run an engine it cannot prove is genuine. Before the native runtime activates, the SDK checks three independent anchors — a **signed release manifest**, **per-artifact hashes**, and an **offline license** — and every one must pass. Each answers a different question, and the chain is ordered: nothing downstream is trusted until the anchor above it is. All three run locally against keys embedded in the wheel; none touches the network.

## Where the anchors live

A verified install lands under `$TELYS_HOME/runtime/<platform>/` (for example `runtime/macos-arm64/`). Each anchor consumes these files:

| File                                         | Consumed by                                                            |
| -------------------------------------------- | ---------------------------------------------------------------------- |
| `telys_manifest.json`                        | Anchor 1 — the release manifest (versions + expected artifact hashes). |
| `telys_manifest.sig`                         | Anchor 1 — RS256 / PKCS#1 v1.5 signature over the manifest bytes.      |
| `libty_runtime.<ext>`, `libame_kernel.<ext>` | Anchor 2 — the native libraries whose SHA-256 is checked.              |
| `license.jwt`                                | Anchor 3 — the offline license token.                                  |

The public keys the SDK trusts ship **inside the wheel**, so verification needs no key server:

* `release_public_key()` → `telys/_keys/telys_release_pub.pem` (verifies the manifest)
* `license_public_key()` → `telys/_keys/telys_license_pub.pem` (verifies the license)

Both require the `cryptography` package, a hard SDK dependency.

## Anchor 1 — the signed release manifest

The manifest lists the release version and the expected SHA-256 of every artifact. Its signature is checked over the **exact bytes** of `telys_manifest.json`:

```python
from telys.verify import verify_manifest, release_public_key

# RS256 / PKCS#1 v1.5 + SHA-256 over the exact manifest bytes.
# Defaults to the embedded release public key.
manifest = verify_manifest(manifest_bytes, signature)   # -> trusted manifest dict
```

`verify_manifest(manifest_bytes, signature, pubkey=None)` verifies the RSA signature and returns the manifest dict only if it is intact. The signature covers the raw bytes, so re-serializing or editing a single character invalidates it. Once it passes, the versions and hashes inside the manifest are trusted — which is what makes Anchor 2 meaningful.

{% hint style="info" %}
The manifest is the root of the chain: the hashes Anchor 2 checks live **inside** this signed manifest. An unsigned or forged manifest would carry worthless hashes, so its signature is verified first.
{% endhint %}

## Anchor 2 — per-artifact SHA-256

For each artifact in the trusted manifest, the SDK recomputes the file's SHA-256 and compares it to the promised value **in constant time**:

```python
from telys.verify import verify_artifact, sha256_file

# Recomputes SHA-256 of the file and compares to the expected hash
# (from the verified manifest) in constant time. Raises on mismatch.
verify_artifact("libty_runtime.dylib", expected_sha256)

# The underlying primitive, if you want the digest itself:
digest = sha256_file("libty_runtime.dylib")   # hex SHA-256 string
```

A swapped, patched, or truncated `libty_runtime` or `libame_kernel` produces a different digest and is rejected. Constant-time comparison prevents probing a mismatch byte-by-byte through timing.

## Anchor 3 — the offline license

The last anchor proves this machine is entitled to run Telys. It is strict and entirely offline:

```python
import datetime
from telys.verify import verify_license

now = int(datetime.datetime.now(datetime.timezone.utc).timestamp())  # verify_license wants a Unix int
claims = verify_license(license_jwt, now=now)   # strict, offline, RS256
print(claims["products"]["telys"])              # tier + features
```

`verify_license(token, pubkey=None, *, now, issuer=None, audience=None, product="telys")` validates `license.jwt` against the embedded license public key and:

* **pins the algorithm to RS256** and rejects any token with a `crit` header;
* checks `iss` (default `https://license.algenta.ai`) and `aud` (default `telys-runtime`, `algenta-runtime`);
* requires `ver == 2` (the `SUPPORTED_LICENSE_VER`);
* checks `exp` against `now` plus a grace window;
* reads the `products.telys` entitlement (tier + features).

The defaults are constants in `telys.verify`:

| Constant                    | Default                            |
| --------------------------- | ---------------------------------- |
| `DEFAULT_LICENSE_ISSUER`    | `https://license.algenta.ai`       |
| `DEFAULT_LICENSE_AUDIENCES` | `telys-runtime`, `algenta-runtime` |
| `SUPPORTED_LICENSE_VER`     | `2`                                |
| `PRODUCT`                   | `telys`                            |

The offline check with a grace window on `exp` means a short outage or travel does not lock you out of a provisioned install. See [**Offline licenses & verification**](/licensing/offline-licenses.md).

## Fail-closed, native-only

The three anchors compose into one rule: an install that does not verify does not run. A verified install is **native-only** — `load_runtime()` loads the signed native runtime and never downgrades a verified install to unverified code; if the runtime cannot import, it raises `RuntimeNotInstalled`. Importing the package activates only a verified install's `pysite/`, and is a silent no-op otherwise.

{% hint style="warning" %}
You can override the anchors via environment — `TELYS_RELEASE_PUBKEY` / `TELYS_RELEASE_PUBKEY_FILE`, `TELYS_LICENSE_PUBKEY` / `TELYS_LICENSE_PUBKEY_FILE`, `TELYS_LICENSE_ISSUER`, and `TELYS_LICENSE_AUDIENCE` — to point at keys of your own, for example a staging release key. In production, leave the embedded PEMs and default constants in place; overriding them means trusting keys you supply.
{% endhint %}

## Next steps

<table data-view="cards"><thead><tr><th></th><th></th><th data-hidden data-card-target data-type="content-ref"></th></tr></thead><tbody><tr><td><strong>Verify the runtime signature</strong></td><td>Run the three-anchor chain yourself, step by step.</td><td><a href="/pages/as3JvHboA5RxokqNHpAw">/pages/as3JvHboA5RxokqNHpAw</a></td></tr><tr><td><strong>Security overview</strong></td><td>The whole posture and the threat model.</td><td><a href="/pages/jLlQKGv5GwnJU5gn4Frl">/pages/jLlQKGv5GwnJU5gn4Frl</a></td></tr><tr><td><strong>The signed runtime &#x26; trust model</strong></td><td>How the anchors fit into loading the engine.</td><td><a href="/pages/VmHkD0an28Ww8yTFnwpS">/pages/VmHkD0an28Ww8yTFnwpS</a></td></tr><tr><td><strong>Signature verification failures</strong></td><td>What to do when an anchor does not pass.</td><td><a href="/pages/0eykLEyLKnupmpNlVgH9">/pages/0eykLEyLKnupmpNlVgH9</a></td></tr></tbody></table>

Next: run the chain in [**Verify the runtime signature**](/security/runtime-signature-verification.md).


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