HarmonyOS AES生成秘钥

aes生成的key encodeToString 可参考以下代码demo实例：

import { cryptoFramework } from '@kit.CryptoArchitectureKit';
import { util } from '@kit.ArkTS';

@Entry
@Component
struct AESCBCCrypto {
  @State message: string = '点击开始';
  build() {
    Row() {
      Column() {
        Text(this.message)
          .fontSize(50)
          .fontWeight(FontWeight.Bold)
          .onClick(() => {
            testSyncGenerateAesKey()
          })
      }
      .width('100%')
    }
    .height('100%')
  }
}
async function testSyncGenerateAesKey() {
  // 创建SymKeyGenerator实例
  let symKeyGenerator = cryptoFramework.createSymKeyGenerator('AES256');
  // 使用密钥生成器随机生成对称密钥
  let promiseSymKey = symKeyGenerator.generateSymKeySync();
  // 获取对称密钥的二进制数据，输出256位密钥。长度为32字节
  let encodedKey = promiseSymKey.getEncoded();
  console.info('key hex:' + encodedKey.data);
  // console.info('key hex:' + encodedKey);
  let base64 = new util.Base64Helper();
  let keyString = await base64.encodeToString(encodedKey.data);
  let keyString1 = base64.encodeToStringSync(encodedKey.data);
  // console.info('key stringify:' + JSON.stringify(keyString));
  console.info('key string:' + keyString);
  console.info('key string1:' + keyString1);
}