# HMAC (ArkTS)


A Hash-based Message Authentication Code (HMAC) is a specific type of message authentication code (MAC) involving a cryptographic has function and a secret cryptographic key. For details about the scenarios and supported algorithm specifications, see [HMAC Overview and Algorithm Specifications](huks-hmac-overview.md).



## How to Develop

**Key Generation**

1. Set the key alias.

2. Initialize the key property set.

3. Use [generateKeyItem](../../reference/apis-universal-keystore-kit/js-apis-huks.md#huksgeneratekeyitem9) to generate a key. For details about the HMAC specifications supported, see [huks-key-generation-overview.md#supported-algorithms).

You can also import a key. For details about the supported algorithms, see [Supported Algorithms](huks-key-import-overview.md#supported-algorithms).

**HMAC Generation**

1. Obtain the key alias.

2. Obtains the data to be calculated.

3. Use [initSession](../../reference/apis-universal-keystore-kit/js-apis-huks.md#huksinitsession9) to initialize a key session. The session handle is returned after the initialization.

4. Use [finishSession](../../reference/apis-universal-keystore-kit/js-apis-huks.md#huksfinishsession9) to obtain the hashed data.


```ts
/*
 * Perform HMAC calculation using promise-based APIs.
 */
import { huks } from '@kit.UniversalKeystoreKit';

let HmackeyAlias = 'test_HMAC';
let handle: number;
let plainText = '123456';
let hashData: Uint8Array;

function StringToUint8Array(str: String) {
  let arr: number[] = new Array();
  for (let i = 0, j = str.length; i < j; ++i) {
    arr.push(str.charCodeAt(i));
  }
  return new Uint8Array(arr);
}

function Uint8ArrayToString(fileData: Uint8Array) {
  let dataString = '';
  for (let i = 0; i < fileData.length; i++) {
    dataString += String.fromCharCode(fileData[i]);
  }
  return dataString;
}

function GetHMACProperties() {
  const properties: Array<huks.HuksParam> = [{
    tag: huks.HuksTag.HUKS_TAG_ALGORITHM,
    value: huks.HuksKeyAlg.HUKS_ALG_HMAC
  }, {
    tag: huks.HuksTag.HUKS_TAG_KEY_SIZE,
    value: huks.HuksKeySize.HUKS_AES_KEY_SIZE_256
  }, {
    tag: huks.HuksTag.HUKS_TAG_PURPOSE,
    value: huks.HuksKeyPurpose.HUKS_KEY_PURPOSE_MAC
  }, {
    tag: huks.HuksTag.HUKS_TAG_DIGEST,
    value: huks.HuksKeyDigest.HUKS_DIGEST_SHA384,
  }];
  return properties;
}

async function GenerateHMACKey() {
  /*
  * Simulate the key generation scenario.
  * 1. Set the key alias.
  */
  /*
  * 2. Obtain the parameters for key generation.
  */
  let genProperties = GetHMACProperties();
  let options: huks.HuksOptions = {
    properties: genProperties
  }
  /*
  * 3. Call generateKeyItem to generate a key.
  */
  await huks.generateKeyItem(HmackeyAlias, options)
    .then((data) => {
      console.info(`promise: generate HMAC Key success`);
    }).catch((error: Error) => {
      console.error(`promise: generate HMAC Key failed, ${JSON.stringify(error)}`);
    })
}

async function HMACData() {
  /*
  * Simulate the HMAC scenario.
  * 1. Obtain the key alias.
  */
  /*
  * 2. Obtain the data to be hashed.
  */
  /*
  * 3. Obtain HMAC algorithm parameter settings.
  */
  let hmacProperties = GetHMACProperties();
  let options: huks.HuksOptions = {
    properties: hmacProperties,
    inData: StringToUint8Array(plainText)
  }
  /*
  * 4. Call initSession to obtain a session handle.
  */
  await huks.initSession(HmackeyAlias, options)
    .then((data) => {
      handle = data.handle;
    }).catch((error: Error) => {
      console.error(`promise: init EncryptData failed, ${JSON.stringify(error)}`);
    })
  /*
  * 5. Call finishSession to obtain the HMAC result.
  */
  await huks.finishSession(handle, options)
    .then((data) => {
      console.info(`promise: HMAC data success, data is ` + Uint8ArrayToString(data.outData as Uint8Array));
      hashData = data.outData as Uint8Array;
    }).catch((error: Error) => {
      console.error(`promise: HMAC data failed, ${JSON.stringify(error)}`);
    })
}
```