# Specifying the User for Key Operations (for System Applications Only)

To implement isolation and access control for key data, HUKS provides APIs with the user ID specified for concurrent key operations initiated by multiple users.
>**NOTE**<br>
> The mini-system devices do not support the operation described in this topic.

## Constraints

- The range of the caller's user ID is **0** to **99**, including **0** and **99**.
- The APIs are available only for system applications.

## Available APIs

APIs with the **userId** parameter are provided as enhancement to existing APIs.

When using these APIs, observe the following:

1. You can pass in [HUKS_TAG_AUTH_STORAGE_LEVEL](../../reference/apis-universal-keystore-kit/_huks_type_api.md#oh_huks_authstoragelevel) in **options** to specify the security level for the key stored.
2. If **HUKS_TAG_AUTH_STORAGE_LEVEL** is not specified in **options**, the key can be accessed only after the first unlock of the device by default, which is equivalent to passing in [HUKS_AUTH_STORAGE_LEVEL_CE](../../reference/apis-universal-keystore-kit/_huks_type_api.md#oh_huks_authstoragelevel).

The algorithm specifications and the usage of the APIs are the same as those of the APIs without **userId**.

| API with userId| Description| API Without userId|
| -------- | -------- | ----------| 
| [generateKeyItemAsUser](../../reference/apis-universal-keystore-kit/js-apis-huks-sys.md#huksgeneratekeyitemasuser)              |   Generates a key.          |  [generateKeyItem](huks-key-generation-arkts.md)             |
| [deleteKeyItemAsUser](../../reference/apis-universal-keystore-kit/js-apis-huks-sys.md#huksdeletekeyitemasuser)                  |   Deletes a key.          |  [deleteKeyItem](huks-delete-key-arkts.md)               |
| [importKeyItemAsUser](../../reference/apis-universal-keystore-kit/js-apis-huks-sys.md#huksimportkeyitemasuser)                  |   Imports a key in plaintext.     |  [importKeyItem](huks-import-key-in-plaintext-arkts.md)                |
| [importWrappedKeyItemAsUser](../../reference/apis-universal-keystore-kit/js-apis-huks-sys.md#huksimportwrappedkeyitemasuser)    |  Imports an encrypted key.       |  [importWrappedKeyItem](huks-import-wrapped-key-arkts.md)             |
| [exportKeyItemAsUser](../../reference/apis-universal-keystore-kit/js-apis-huks-sys.md#huksexportkeyitemasuser)                  |   Exports a key.       |  [exportKeyItem](huks-export-key-arkts.md)                |
| [getKeyItemPropertiesAsUser](../../reference/apis-universal-keystore-kit/js-apis-huks-sys.md#huksgetkeyitempropertiesasuser)    |  Obtains key properties.    |  [getKeyItemProperties](huks-obtain-key-properties-arkts.md)             |
| [hasKeyItemAsUser](../../reference/apis-universal-keystore-kit/js-apis-huks-sys.md#hukshaskeyitemasuser)                        |  Checks whether a key exists.   |  [hasKeyItem](huks-check-key-arkts.md)               |
| [initSessionAsUser](../../reference/apis-universal-keystore-kit/js-apis-huks-sys.md#huksinitsessionasuser)                      |  Initializes a key session.      |  initSession in [encryption and decryption](huks-encryption-decryption-arkts.md), [signing and signature verification](huks-signing-signature-verification-arkts.md), [key agreement](huks-key-agreement-arkts.md), and [key derivation](huks-key-derivation-arkts.md)          |
| [attestKeyItemAsUser](../../reference/apis-universal-keystore-kit/js-apis-huks-sys.md#huksattestkeyitemasuser)                  |  Performs non-anonymous key attestation.   |  [attestKeyItem](huks-key-attestation-arkts.md)                |
| [anonAttestKeyItemAsUser](../../reference/apis-universal-keystore-kit/js-apis-huks-sys.md#huksanonattestkeyitemasuser)          | Performs anonymous key attestation.    |  [anonAttestKeyItem](huks-key-anon-attestation-arkts.md)                |