Encryption and Decryption with an AES Symmetric Key (CBC Mode)

For details about the algorithm specifications, see AES.

Encryption

1. Use cryptoFramework.createSymKeyGenerator and SymKeyGenerator.generateSymKey to generate a 128-bit AES symmetric key (SymKey).

   In addition to the example in this topic, AES and Randomly Generating a Symmetric Key may help you better understand how to generate an AES symmetric key. Note that the input parameters in the reference documents may be different from those in the example below.

2. Use cryptoFramework.createCipher with the string parameter 'AES128|CBC|PKCS7' to create a Cipher instance. The key type is AES128, block cipher mode is CBC, and the padding mode is PKCS7.

3. Use Cipher.init to initialize the Cipher instance. In the Cipher.init API, set opMode to CryptoMode.ENCRYPT_MODE (encryption), key to SymKey (the key for encryption), and params to IvParamsSpec corresponding to the CBC mode.

4. If the data to be encrypted is short, you can use Cipher.doFinal after Cipher.init to obtain the encrypted data.

Decryption

1. Use Cipher.init to initialize the Cipher instance. In the Cipher.init API, set opMode to CryptoMode.DECRYPT_MODE (decryption), key to SymKey (the key for decryption), and params to IvParamsSpec corresponding to the CBC mode.

2. If the data to be decrypted is short, you can use Cipher.doFinal after Cipher.init to obtain the decrypted data.

import cryptoFramework from '@ohos.security.cryptoFramework';
import buffer from '@ohos.buffer';

function genIvParamsSpec() {
  let arr = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]; // 16 bytes
  let dataIv = new Uint8Array(arr);
  let ivBlob: cryptoFramework.DataBlob = { data: dataIv };
  let ivParamsSpec: cryptoFramework.IvParamsSpec = {
    algName: "IvParamsSpec",
    iv: ivBlob
  };
  return ivParamsSpec;
}
// Encrypt the message.
async function encryptMessagePromise(symKey: cryptoFramework.SymKey, plainText: cryptoFramework.DataBlob) {
  let cipher = cryptoFramework.createCipher('AES128|CBC|PKCS7');
  let iv = genIvParamsSpec();
  await cipher.init(cryptoFramework.CryptoMode.ENCRYPT_MODE, symKey, iv);
  let cipherData = await cipher.doFinal(plainText);
  return cipherData;
}
// Decrypt the message.
async function decryptMessagePromise(symKey: cryptoFramework.SymKey, cipherText: cryptoFramework.DataBlob) {
  let decoder = cryptoFramework.createCipher('AES128|CBC|PKCS7');
  let iv = genIvParamsSpec();
  await decoder.init(cryptoFramework.CryptoMode.DECRYPT_MODE, symKey, iv);
  let decryptData = await decoder.doFinal(cipherText);
  return decryptData;
}

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 aesCBC() {
  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 = "This is a test";
  let plainText: cryptoFramework.DataBlob = { data: new Uint8Array(buffer.from(message, 'utf-8').buffer) };
  let encryptText = await encryptMessagePromise(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');
  }
}