> 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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```
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