Encryption and Decryption with an SM2 Asymmetric Key Pair

For details about the algorithm specifications, see SM2.

Encryption

1. Use cryptoFramework.createAsyKeyGenerator and AsyKeyGenerator.generateKeyPair to create a 256-bit SM2 asymmetric key pair (KeyPair). The KeyPair object includes a public key (PubKey) and a private key (PriKey).

   In addition to the example in this topic, SM2 and Randomly Generating an Asymmetric Key Pair may help you better understand how to generate an SM2 asymmetric key pair. 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 'SM2_256|SM3' to create a Cipher instance. The key type is SM2_256, and the MD algorithm is SM3.

3. Use Cipher.init to initialize the Cipher instance. In Cipher.init, set opMode to CryptoMode.ENCRYPT_MODE (encryption) and key to KeyPair.PubKey (the key used for encryption).

   No encryption parameter is required for asymmetric key pairs. Therefore, pass in null in params.

4. Use Cipher.doFinal to pass in the plaintext and encrypt it.

   • The output of doFinal may be null. To avoid exceptions, always check whether the result is null before accessing specific data.
   • If the data to be encrypted is considerably long, you can call doFinal() multiple times to pass in and encrypt the data by segment.

Decryption

1. If SM2 is used, the Cipher instance cannot be initialized repeatedly. Use cryptoFramework.createCipher to create a new Cipher instance.

2. Use Cipher.init to initialize the Cipher instance. In Cipher.init, set opMode to CryptoMode.DECRYPT_MODE (decryption) and key to KeyPair.PriKey (the key used for decryption). If SM2 is used, no decryption parameter is required. Therefore, pass in null in params.

3. Use Cipher.doFinal to pass in the ciphertext and decrypt it.

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

// Encrypt the message.
async function encryptMessagePromise(publicKey: cryptoFramework.PubKey, plainText: cryptoFramework.DataBlob) {
  let cipher = cryptoFramework.createCipher('SM2_256|SM3');
  await cipher.init(cryptoFramework.CryptoMode.ENCRYPT_MODE, publicKey, null);
  let encryptData = await cipher.doFinal(plainText);
  return encryptData;
}
// Decrypt the message.
async function decryptMessagePromise(privateKey: cryptoFramework.PriKey, cipherText: cryptoFramework.DataBlob) {
  let decoder = cryptoFramework.createCipher('SM2_256|SM3');
  await decoder.init(cryptoFramework.CryptoMode.DECRYPT_MODE, privateKey, null);
  let decryptData = await decoder.doFinal(cipherText);
  return decryptData;
}
// Generate an SM2 key pair.
async function genKeyPairByData(pubKeyData: Uint8Array, priKeyData: Uint8Array) {
  let pubKeyBlob: cryptoFramework.DataBlob = { data: pubKeyData };
  let priKeyBlob: cryptoFramework.DataBlob = { data: priKeyData };
  let sm2Generator = cryptoFramework.createAsyKeyGenerator('SM2_256');
  let keyPair = await sm2Generator.convertKey(pubKeyBlob, priKeyBlob);
  console.info('convertKey success');
  return keyPair;
}
async function main() {
  let pkData = new Uint8Array([48, 89, 48, 19, 6, 7, 42, 134, 72, 206, 61, 2, 1, 6, 8, 42, 129, 28, 207, 85, 1, 130, 45, 3, 66, 0, 4, 90, 3, 58, 157, 190, 248, 76, 7, 132, 200, 151, 208, 112, 230, 96, 140, 90, 238, 211, 155, 128, 109, 248, 40, 83, 214, 78, 42, 104, 106, 55, 148, 249, 35, 61, 32, 221, 135, 143, 100, 45, 97, 194, 176, 52, 73, 136, 174, 40, 70, 70, 34, 103, 103, 161, 99, 27, 187, 13, 187, 109, 244, 13, 7]);
  let skData = new Uint8Array([48, 49, 2, 1, 1, 4, 32, 54, 41, 239, 240, 63, 188, 134, 113, 31, 102, 149, 203, 245, 89, 15, 15, 47, 202, 170, 60, 38, 154, 28, 169, 189, 100, 251, 76, 112, 223, 156, 159, 160, 10, 6, 8, 42, 129, 28, 207, 85, 1, 130, 45]);
  let keyPair = await genKeyPairByData(pkData, skData);
  let pubKey = keyPair.pubKey;
  let priKey = keyPair.priKey;
  let message = 'This is a test';
  // Decode the string into a Uint8Array in UTF-8 format.
  let plainText: cryptoFramework.DataBlob = { data: new Uint8Array(buffer.from(message, 'utf-8').buffer) };
  let encryptText = await encryptMessagePromise(pubKey, plainText);
  let decryptText = await decryptMessagePromise(priKey, encryptText);
  if (plainText.data.toString() === decryptText.data.toString()) {
    console.info('decrypt ok');
    // Encode the Uint8Array into a string in UTF-8 format.
    let messageDecrypted = buffer.from(decryptText.data).toString('utf-8');
    console.info('decrypted result string:' + messageDecrypted);
  } else {
    console.error('decrypt failed');
  }
}
}