> For the complete documentation index, see [llms.txt](https://docs.payments.thalescloud.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.payments.thalescloud.io/tokenization/implement-tokenization/post-tokenization-requests/visa-cloud-token-framework-ctf/device-binding.md).

# Device binding

This feature allows the Merchant to ask the Issuer to approve the binding between a COF digital card and a device.

The objective of this feature is to increase the assurance level of the digital card through end user verification.

The Issuer can optionally define rules to decline bindings from devices considered insecure. If a device matches one or more rules, D1 automatically declines the binding request. If the Issuer does not define any rules, binding requests are not declined and the Level of Trust remains `YELLOW`.

The following table lists the available rules. For more details, see the D1 onboarding phase.

| Rule name                        | Description                                                                                 |
| -------------------------------- | ------------------------------------------------------------------------------------------- |
| Device types not trusted         | The Issuer can select device types it does not trust. For example, devices of type `WATCH`. |
| Device manufacturer              | The Issuer can list device manufacturers it does not trust.                                 |
| Device manufacturer - OS version | If known, the Issuer can specify an OS version it does not trust.                           |
| Device manufacturer - FW version | If known, the Issuer can specify a firmware version it does not trust.                      |

{% hint style="warning" %}
**Caution**

D1 can apply these rules only if VTS sends the required fields. Today, VTS does not guarantee any specific set of device data. Even if the Issuer defines a rule, D1 cannot ensure that the rule is applied systematically.
{% endhint %}

D1 manages this flow on behalf of the Issuer.

The following diagram shows a high-level flow and highlights the Issuer's involvement in the process.

<figure><img src="/files/0maZM8eKcWc6kD2llt1C" alt=""><figcaption><p>High-level device binding flow.</p></figcaption></figure>

The diagram references [Approve with step-up authentication](/tokenization/implement-tokenization/card-tokenization-request/processing-the-response/approve-with-step-up-authentication.md).

This is the same flow used for Tokenization processing, with the following exceptions:

* The `Customer service` ID\&V method is not supported.
* The `In-app` ID\&V method can be supported within the issuer application through the D1 SDK (please refer to the section [In-app authentication for Visa CTF](/push-provisioning/implement-push-provisioning/implement-view-and-control/in-app-authentication-for-visa-ctf.md)) or through an additional backend API that allows approval of the binding after the authentication has been completed successfully. This is depicted in the following diagram:

<figure><img src="/files/whh6XS6Y6l2utQxaQ5DN" alt=""><figcaption></figcaption></figure>

{% hint style="info" %}
**Note**

The following field mappings apply:

* `tokenReferenceID` = `digitalCardID`
* `deviceIndex` = `bindingReference`
  {% endhint %}


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