# 使用AES对称密钥（GCM模式）分段加解密(ArkTS)


对应的算法规格请查看[对称密钥加解密算法规格：AES](crypto-sym-encrypt-decrypt-spec.md#aes)。


**加密**


1. 调用[cryptoFramework.createSymKeyGenerator](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#cryptoframeworkcreatesymkeygenerator)、[SymKeyGenerator.generateSymKey](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#generatesymkey-1)，生成密钥算法为AES、密钥长度为128位的对称密钥（SymKey）。
   
   如何生成AES对称密钥，开发者可参考下文示例，并结合[对称密钥生成和转换规格：AES](crypto-sym-key-generation-conversion-spec.md#aes)和[随机生成对称密钥](crypto-generate-sym-key-randomly.md)理解，参考文档与当前示例可能存在入参差异，请在阅读时注意区分。

2. 调用[cryptoFramework.createCipher](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#cryptoframeworkcreatecipher)，指定字符串参数'AES128|GCM|PKCS7'，创建对称密钥类型为AES128、分组模式为GCM、填充模式为PKCS7的Cipher实例，用于完成加解密操作。

3. 调用[Cipher.init](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#init-1)，设置模式为加密（CryptoMode.ENCRYPT_MODE），指定加密密钥（SymKey）和GCM模式对应的加密参数（GcmParamsSpec），初始化加密Cipher实例。

4. 将一次传入数据量设置为20字节，多次调用[Cipher.update](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#update-1)，更新数据（明文）。
   
   - 当前单次update长度没有限制，开发者可以根据数据量判断如何调用update。
   - 建议开发者对每次update的结果都判断是否为null，并在结果不为null时取出其中的数据进行拼接，形成完整的密文。因为在不同的规格下，update的结果可能会受到不同影响。
      
      1）比如ECB和CBC模式，始终以分组作为基本单位来加密，并输出本次update产生的加密分组结果。即当本次update操作凑满一个分组就输出密文，没有凑满则此次update输出null，将未加密的数据与下次输入的数据拼接凑分组再输出。等到最后doFinal的时候，将未加密的数据，根据指定的填充模式进行填充，在输出剩余加密结果。解密过程中的update同理。

      2）对于流加密模式（比如CTR和OFB模式），通常密文长度和明文长度相等。

5. 调用[Cipher.doFinal](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#dofinal-1)，获取加密后的数据。
   
   - 由于已使用update传入数据，此处data传入null。
   - doFinal输出结果可能为null，在访问具体数据前，需要先判断结果是否为null，避免产生异常。

6. 读取[GcmParamsSpec](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#gcmparamsspec).authTag作为解密的认证信息。
   
   在GCM模式下，需要从加密后的数据中取出末尾16字节，作为解密时初始化的认证信息。示例中authTag恰好为16字节。


**解密**


1. 调用[Cipher.init](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#init-1)，设置模式为解密（CryptoMode.DECRYPT_MODE），指定解密密钥（SymKey）和GCM模式对应的解密参数（GcmParamsSpec），初始化解密Cipher实例。

2. 将一次传入数据量设置为20字节，多次调用[Cipher.update](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#update-1)，更新数据（密文）。

3. 调用[Cipher.doFinal](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#dofinal-1)，获取解密后的数据。


- 异步方法示例：

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

  function generateRandom(len: number) {
    let rand = cryptoFramework.createRandom();
    let generateRandSync = rand.generateRandomSync(len);
    return generateRandSync;
  }

  function genGcmParamsSpec() {
    let ivBlob = generateRandom(12);
    let arr = [1, 2, 3, 4, 5, 6, 7, 8]; // 8 bytes
    let dataAad = new Uint8Array(arr);
    let aadBlob: cryptoFramework.DataBlob = { data: dataAad };
    arr = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]; // 16 bytes
    let dataTag = new Uint8Array(arr);
    let tagBlob: cryptoFramework.DataBlob = {
      data: dataTag
    }; // The GCM authTag is obtained by doFinal() in encryption and passed in params of init() in decryption.
    let gcmParamsSpec: cryptoFramework.GcmParamsSpec = {
      iv: ivBlob,
      aad: aadBlob,
      authTag: tagBlob,
      algName: "GcmParamsSpec"
    };
    return gcmParamsSpec;
  }
  let gcmParams = genGcmParamsSpec();
  // 分段加密消息
  async function encryptMessageUpdateBySegment(symKey: cryptoFramework.SymKey, plainText: cryptoFramework.DataBlob) {
    let cipher = cryptoFramework.createCipher('AES128|GCM|PKCS7');
    await cipher.init(cryptoFramework.CryptoMode.ENCRYPT_MODE, symKey, gcmParams);
    let updateLength = 20; // 假设以20字节为单位进行分段update，实际并无要求
    let cipherText = new Uint8Array();
    for (let i = 0; i < plainText.data.length; i += updateLength) {
      let updateMessage = plainText.data.subarray(i, i + updateLength);
      let updateMessageBlob: cryptoFramework.DataBlob = { data: updateMessage };
      // 分段update
      let updateOutput = await cipher.update(updateMessageBlob);
      // 把update的结果拼接起来，得到密文（有些情况下还需拼接doFinal的结果，这取决于分组模式
      // 和填充模式，本例中GCM模式的doFinal结果只包含authTag而不含密文，所以不需要拼接）
      let mergeText = new Uint8Array(cipherText.length + updateOutput.data.length);
      mergeText.set(cipherText);
      mergeText.set(updateOutput.data, cipherText.length);
      cipherText = mergeText;
    }
    gcmParams.authTag = await cipher.doFinal(null);
    let cipherBlob: cryptoFramework.DataBlob = { data: cipherText };
    return cipherBlob;
  }
  // 分段解密消息
  async function decryptMessagePromise(symKey: cryptoFramework.SymKey, cipherText: cryptoFramework.DataBlob) {
    let decoder = cryptoFramework.createCipher('AES128|GCM|PKCS7');
    await decoder.init(cryptoFramework.CryptoMode.DECRYPT_MODE, symKey, gcmParams);
    let updateLength = 20; // 假设以20字节为单位进行分段update，实际并无要求
    let decryptText = new Uint8Array();
    for (let i = 0; i < cipherText.data.length; i += updateLength) {
      let updateMessage = cipherText.data.subarray(i, i + updateLength);
      let updateMessageBlob: cryptoFramework.DataBlob = { data: updateMessage };
      // 分段update
      let updateOutput = await decoder.update(updateMessageBlob);
      // 把update的结果拼接起来，得到明文
      let mergeText = new Uint8Array(decryptText.length + updateOutput.data.length);
      mergeText.set(decryptText);
      mergeText.set(updateOutput.data, decryptText.length);
      decryptText = mergeText;
    }
    let decryptData = await decoder.doFinal(null);
    if (decryptData == null) {
      console.info('GCM decrypt success, decryptData is null');
    }
    let decryptBlob: cryptoFramework.DataBlob = { data: decryptText };
    return decryptBlob;
  }
  async function genSymKeyByData(symKeyData: Uint8Array) {
    let symKeyBlob: cryptoFramework.DataBlob = { data: symKeyData };
    let aesGenerator = cryptoFramework.createSymKeyGenerator('AES128');
    let symKey = await aesGenerator.convertKey(symKeyBlob);
    console.info('convertKey success');
    return symKey;
  }
  async function aes() {
    let keyData = new Uint8Array([83, 217, 231, 76, 28, 113, 23, 219, 250, 71, 209, 210, 205, 97, 32, 159]);
    let symKey = await genSymKeyByData(keyData);
    let message = "aaaaa.....bbbbb.....ccccc.....ddddd.....eee"; // 假设信息总共43字节，根据utf-8解码后，也是43字节
    let plainText: cryptoFramework.DataBlob = { data: new Uint8Array(buffer.from(message, 'utf-8').buffer) };
    let encryptText = await encryptMessageUpdateBySegment(symKey, plainText);
    let decryptText = await decryptMessagePromise(symKey, encryptText);
    if (plainText.data.toString() === decryptText.data.toString()) {
      console.info('decrypt ok');
      console.info('decrypt plainText: ' + buffer.from(decryptText.data).toString('utf-8'));
    } else {
      console.error('decrypt failed');
    }
  }
  ```

- 同步方法示例：

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

  function generateRandom(len: number) {
    let rand = cryptoFramework.createRandom();
    let generateRandSync = rand.generateRandomSync(len);
    return generateRandSync;
  }
  
  function genGcmParamsSpec() {
    let ivBlob = generateRandom(12);
    let arr = [1, 2, 3, 4, 5, 6, 7, 8]; // 8 bytes
    let dataAad = new Uint8Array(arr);
    let aadBlob: cryptoFramework.DataBlob = { data: dataAad };
    arr = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]; // 16 bytes
    let dataTag = new Uint8Array(arr);
    let tagBlob: cryptoFramework.DataBlob = {
      data: dataTag
    }; // The GCM authTag is obtained by doFinal() in encryption and passed in params of init() in decryption.
    let gcmParamsSpec: cryptoFramework.GcmParamsSpec = {
      iv: ivBlob,
      aad: aadBlob,
      authTag: tagBlob,
      algName: "GcmParamsSpec"
    };
    return gcmParamsSpec;
  }
  let gcmParams = genGcmParamsSpec();
  // 分段加密消息
  function encryptMessageUpdateBySegment(symKey: cryptoFramework.SymKey, plainText: cryptoFramework.DataBlob) {
    let cipher = cryptoFramework.createCipher('AES128|GCM|PKCS7');
    cipher.initSync(cryptoFramework.CryptoMode.ENCRYPT_MODE, symKey, gcmParams);
    let updateLength = 20; // 假设以20字节为单位进行分段update，实际并无要求
    let cipherText = new Uint8Array();
    for (let i = 0; i < plainText.data.length; i += updateLength) {
      let updateMessage = plainText.data.subarray(i, i + updateLength);
      let updateMessageBlob: cryptoFramework.DataBlob = { data: updateMessage };
      // 分段update
      let updateOutput = cipher.updateSync(updateMessageBlob);
      // 把update的结果拼接起来，得到密文（有些情况下还需拼接doFinal的结果，这取决于分组模式
      // 和填充模式，本例中GCM模式的doFinal结果只包含authTag而不含密文，所以不需要拼接）
      let mergeText = new Uint8Array(cipherText.length + updateOutput.data.length);
      mergeText.set(cipherText);
      mergeText.set(updateOutput.data, cipherText.length);
      cipherText = mergeText;
    }
    gcmParams.authTag = cipher.doFinalSync(null);
    let cipherBlob: cryptoFramework.DataBlob = { data: cipherText };
    return cipherBlob;
  }
  // 分段解密消息
  function decryptMessage(symKey: cryptoFramework.SymKey, cipherText: cryptoFramework.DataBlob) {
    let decoder = cryptoFramework.createCipher('AES128|GCM|PKCS7');
    decoder.initSync(cryptoFramework.CryptoMode.DECRYPT_MODE, symKey, gcmParams);
    let updateLength = 20; // 假设以20字节为单位进行分段update，实际并无要求
    let decryptText = new Uint8Array();
    for (let i = 0; i < cipherText.data.length; i += updateLength) {
      let updateMessage = cipherText.data.subarray(i, i + updateLength);
      let updateMessageBlob: cryptoFramework.DataBlob = { data: updateMessage };
      // 分段update
      let updateOutput = decoder.updateSync(updateMessageBlob);
      // 把update的结果拼接起来，得到明文
      let mergeText = new Uint8Array(decryptText.length + updateOutput.data.length);
      mergeText.set(decryptText);
      mergeText.set(updateOutput.data, decryptText.length);
      decryptText = mergeText;
    }
    let decryptData = decoder.doFinalSync(null);
    if (decryptData == null) {
      console.info('GCM decrypt success, decryptData is null');
    }
    let decryptBlob: cryptoFramework.DataBlob = { data: decryptText };
    return decryptBlob;
  }
  function genSymKeyByData(symKeyData: Uint8Array) {
    let symKeyBlob: cryptoFramework.DataBlob = { data: symKeyData };
    let aesGenerator = cryptoFramework.createSymKeyGenerator('AES128');
    let symKey = aesGenerator.convertKeySync(symKeyBlob);
    console.info('convertKeySync success');
    return symKey;
  }
  function main() {
    let keyData = new Uint8Array([83, 217, 231, 76, 28, 113, 23, 219, 250, 71, 209, 210, 205, 97, 32, 159]);
    let symKey = genSymKeyByData(keyData);
    let message = "aaaaa.....bbbbb.....ccccc.....ddddd.....eee"; // 假设信息总共43字节，根据utf-8解码后，也是43字节
    let plainText: cryptoFramework.DataBlob = { data: new Uint8Array(buffer.from(message, 'utf-8').buffer) };
    let encryptText = encryptMessageUpdateBySegment(symKey, plainText);
    let decryptText = decryptMessage(symKey, encryptText);
    if (plainText.data.toString() === decryptText.data.toString()) {
      console.info('decrypt ok');
      console.info('decrypt plainText: ' + buffer.from(decryptText.data).toString('utf-8'));
    } else {
      console.error('decrypt failed');
    }
  }

  ```