# Verifying signatures

Every webhook delivery includes an `Aviowiki-Signature` header that you should use to verify the request is genuinely from aviowiki.

The header format is:

```
Aviowiki-Signature: t=1715782200000,v1=5257a869e7ecebeda32affa62cdca3fa51cad7e77a0e56ff536d0ce8e108d8f9
```

| Part | Description                                                     |
| ---- | --------------------------------------------------------------- |
| `t`  | Unix timestamp in milliseconds when the signature was generated |
| `v1` | HMAC-SHA256 signature in lowercase hex                          |

### Verification Steps

1. Extract the timestamp (`t`) and signature (`v1`) from the header
2. Construct the signed message: `{timestamp}.{raw_request_body}`
3. Compute HMAC-SHA256 of the message using your subscription's `secret` as the key
4. Compare your computed signature with `v1`
5. Optionally, check that the timestamp is within an acceptable tolerance (e.g. 5 minutes) to prevent replay attacks

{% tabs %}
{% tab title="Python" %}

```python
import hmac
import hashlib
import time

def verify_signature(payload, signature_header, secret, tolerance_ms=300000):
    parts = dict(item.split("=", 1) for item in signature_header.split(","))
    timestamp = int(parts["t"])
    expected_sig = parts["v1"]

    # Check timestamp tolerance (5 minutes)
    if time.time() * 1000 - timestamp > tolerance_ms:
        return False

    message = f"{timestamp}.{payload}"
    computed = hmac.new(
        secret.encode("utf-8"),
        message.encode("utf-8"),
        hashlib.sha256
    ).hexdigest()

    return hmac.compare_digest(computed, expected_sig)
```

{% endtab %}

{% tab title="Java" %}

```java
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;

public boolean verifySignature(String payload, String signatureHeader,
                               String secret, long toleranceMs) {
    String[] parts = signatureHeader.split(",");
    long timestamp = Long.parseLong(parts[0].split("=")[1]);
    String expectedSig = parts[1].split("=")[1];

    if (System.currentTimeMillis() - timestamp > toleranceMs) {
        return false;
    }

    String message = timestamp + "." + payload;
    Mac mac = Mac.getInstance("HmacSHA256");
    mac.init(new SecretKeySpec(
        secret.getBytes(StandardCharsets.UTF_8), "HmacSHA256"));
    byte[] hash = mac.doFinal(message.getBytes(StandardCharsets.UTF_8));

    StringBuilder hex = new StringBuilder();
    for (byte b : hash) {
        hex.append(String.format("%02x", b));
    }

    return hex.toString().equals(expectedSig);
}
```

{% endtab %}
{% endtabs %}


---

# Agent Instructions: Querying This Documentation

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Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.aviowiki.com/webhooks/verifying-signatures.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.