> For the complete documentation index, see [llms.txt](https://docs.licensespring.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.licensespring.com/license-api/license-api-authorization/response-signature.md).

# Response Signature

### Overview

Response objects from License API endpoints for activating and checking licenses contain a `license_signature` value, which is an HMAC-SHA256 signature used to verify the authenticity of the response. This mechanism ensures protection against counterfeit licensing servers and man-in-the-middle attacks.

### License Signature Details

When a webhook response is received, it includes a **license\_signature**. This signature is a secure hash generated using a server-side private key and is based on a specific format of the signing string.

#### Signing String Format

The string to be signed is constructed as follows:

```
LOWERCASE(HARDWARE_ID#USER_EMAIL_OR_LICENSE_KEY#VALIDITY_PERIOD)
```

#### Example Activation Request and Response

Request:

```json
{
  "hardware_id": "A53F-0CBC-15FC-7E81-BF35-A720-A575-7C0C-8815-0463-DB78-E674-D140-CF15-85BB-EC01",
  "license_key": "FUH3-4E7A-LZJL-7JTP",
  "product": "TP"
}
```

Response:

```json
{
  "license_signature": "60c22a575a67f5b2a1e9ff3fe204363046f1e5d097b8ebb468d903d0aaf739ac...",
  "validity_period": "2019-06-15T00:00:00.000Z",
  "license_type": "subscription",
  ...
}
```

#### Constructed Signing String

Based on the above request and response:

```
a53f-0cbc-15fc-7e81-bf35-a720-a575-7c0c-8815-0463-db78-e674-d140-cf15-85bb-ec01#fuh3-4e7a-lzjl-7jtp#2019-06-15t00:00:00.000z
```

### Verifying the License Signature

You can use the server's public key to verify the **license\_signature**. By validating the signature, you ensure the response originates from LicenseSpring's trusted servers.

Download the server public key from the link below to implement signature verification using the example provided:

{% file src="/files/MuIwiFmMUjvrVaJF1UJj" %}

### Code Sample

{% code title="verify-signature.js" %}

```javascript
import crypto from 'node:crypto'
import dayjs from 'dayjs'
import utc from 'dayjs/plugin/utc.js'

dayjs.extend(utc)

const response = {
  // ... truncated license response ...
  "license_key": "163U-AKLB-5BNJ-VYOF-4567",
  "hardware_id": "6993f191bca2346c4015be4ff158805da70f10cd7d82aedd11dd38c2b47025a2",
  "validity_period": null,
  "license_signature": "VAkfjWGvQDl00YkjYS/1oCz........3HtzwFt8tQ=",
};

const signingString = `${
  licenseResponse.hardware_id
}#${
  licenseResponse.username
    ? licenseResponse.username.split('|')[0]
    : licenseResponse.license_key
}#${
  licenseResponse.validity_period ? dayjs(licenseResponse.validity_period).toISOString() : ''
}`.toLowerCase();

const verifier = crypto.createVerify('RSA-SHA256');
verifier.update(signingString);
const result = verifier.verify(publicKey, licenseResponse.license_signature, 'base64');

console.log(result); // if signature is valid, this will be "true"
```

{% endcode %}


---

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## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

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

```
GET https://docs.licensespring.com/license-api/license-api-authorization/response-signature.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

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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.