# 使用HKDF进行密钥派生

对应算法规格请查看[密钥派生算法规格：HKDF](crypto-key-derivation-overview.md#hkdf算法)。

## 开发步骤
1. 构造[HKDFSpec](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#hkdfspec12)对象，作为密钥派生参数进行密钥派生。
   
   HKDFSpec是[KdfSpec](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#kdfspec11)的子类，需要指定：

   - algName：指定算法'HKDF'。
   - key：原始密钥材料。
      如果使用string类型，需要直接传入用于密钥派生的数据，而不是HexString、base64等字符串类型。同时需要确保该字符串为utf-8编码，否则派生结果会有差异。
   - salt：盐值。
   - info：可选的上下文与应用相关信息， 可为空，用于拓展短密钥。
   - keySize：目标密钥的字节长度，需要为正整数。

2. 调用[cryptoFramework.createKdf](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#cryptoframeworkcreatekdf11)，指定字符串参数'HKDF|SHA256|EXTRACT_AND_EXPAND'，创建密钥派生算法为HKDF、HMAC函数摘要算法为SHA256、模式为提取和拓展的密钥派生函数对象（Kdf）。

3. 输入HKDFSpec对象，调用[Kdf.generateSecret](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#generatesecret-2)进行密钥派生。
   
   Kdf.generateSecret的多种调用形式如表所示。
   
   | 接口名 | 返回方式 | 
   | -------- | -------- |
   | generateSecret(params: KdfSpec, callback: AsyncCallback<DataBlob>): void | callback异步生成 | 
   | generateSecret(params: KdfSpec): Promise<DataBlob> | Promise异步生成 | 
   | generateSecretSync(params: KdfSpec): DataBlob | 同步生成 | 

- 通过await返回结果：

  ```ts
  import { cryptoFramework } from '@kit.CryptoArchitectureKit';
  import { buffer } from '@kit.ArkTS';

  async function kdfAwait() {
    let keyData = new Uint8Array(buffer.from("012345678901234567890123456789", "utf-8").buffer);
    let saltData = new Uint8Array(buffer.from("0123456789", "utf-8").buffer);
    let infoData = new Uint8Array(buffer.from("infostring", "utf-8").buffer);
    let spec: cryptoFramework.HKDFSpec = {
      algName: 'HKDF',
      key: keyData,
      salt: saltData,
      info: infoData,
      keySize: 32
    };
    let kdf = cryptoFramework.createKdf('HKDF|SHA256|EXTRACT_AND_EXPAND');
    let secret = await kdf.generateSecret(spec);
    console.info("key derivation output is " + secret.data);
  }
  ```

- 通过Promise返回结果：

  ```ts
  import { cryptoFramework } from '@kit.CryptoArchitectureKit';
  import { BusinessError } from '@kit.BasicServicesKit';
  import { buffer } from '@kit.ArkTS';

  function kdfPromise() {
    let keyData = new Uint8Array(buffer.from("012345678901234567890123456789", "utf-8").buffer);
    let saltData = new Uint8Array(buffer.from("0123456789", "utf-8").buffer);
    let infoData = new Uint8Array(buffer.from("infostring", "utf-8").buffer);
    let spec: cryptoFramework.HKDFSpec = {
      algName: 'HKDF',
      key: keyData,
      salt: saltData,
      info: infoData,
      keySize: 32
    };
    let kdf = cryptoFramework.createKdf('HKDF|SHA256|EXTRACT_AND_EXPAND');
    let kdfPromise = kdf.generateSecret(spec);
    kdfPromise.then((secret) => {
      console.info("key derivation output is " + secret.data);
    }).catch((error: BusinessError) => {
      console.error("key derivation error.");
    });
  }
  ```

- 通过同步方式返回结果：

  ```ts
  import { cryptoFramework } from '@kit.CryptoArchitectureKit';
  import { BusinessError } from '@kit.BasicServicesKit';
  import { buffer } from '@kit.ArkTS';
  
  function kdfSync() {
    let keyData = new Uint8Array(buffer.from("012345678901234567890123456789", "utf-8").buffer);
    let saltData = new Uint8Array(buffer.from("0123456789", "utf-8").buffer);
    let infoData = new Uint8Array(buffer.from("infostring", "utf-8").buffer);
    let spec: cryptoFramework.HKDFSpec = {
      algName: 'HKDF',
      key: keyData,
      salt: saltData,
      info: infoData,
      keySize: 32
    };
    let kdf = cryptoFramework.createKdf('HKDF|SHA256|EXTRACT_AND_EXPAND');
    let secret = kdf.generateSecretSync(spec);
    console.info("[Sync]key derivation output is " + secret.data);
  }
  ```