Converting Binary Data into a Symmetric Key

This topic uses 3DES and HMAC as an example to describe how to convert binary data into a symmetric key. That is, convert a piece of external or internal binary data into a key object for subsequent operations, such as encryption and decryption.

Converting Binary Data into a 3DES Key

For details about the algorithm specifications, see 3DES.

1. Obtain the 3DES key binary data and encapsulate it into a DataBlob object.

2. Use cryptoFramework.createSymKeyGenerator with the string parameter '3DES192' to create a symmetric key generator (SymKeyGenerator) object for a 192-bit 3DES key.

3. Use SymKeyGenerator.convertKey to convert the binary data into a symmetric key (SymKey).

4. Use SymKey.getEncoded to obtain the binary data of the key.

Example: Convert binary data into a 192-bit 3DES key (using callback-based APIs).

import cryptoFramework from '@ohos.security.cryptoFramework';
import { BusinessError } from '@ohos.base';

function genKeyMaterialBlob(): cryptoFramework.DataBlob {
  let arr = [
    0xba, 0x3d, 0xc2, 0x71, 0x21, 0x1e, 0x30, 0x56,
    0xad, 0x47, 0xfc, 0x5a, 0x46, 0x39, 0xee, 0x7c,
    0xba, 0x3b, 0xc2, 0x71, 0xab, 0xa0, 0x30, 0x72]; // The key length is 192 bits, that is, 24 bytes.
  let keyMaterial = new Uint8Array(arr);
  return { data: keyMaterial };
}

function testConvertSymKey() {
  // Create a SymKeyGenerator instance.
  let symKeyGenerator = cryptoFramework.createSymKeyGenerator('3DES192');
  // Convert the data into a symmetric key.
  let keyMaterialBlob = genKeyMaterialBlob();
  try {
    symKeyGenerator.convertKey(keyMaterialBlob, (error, key) => {
      if (error) {// If the service logic fails to be executed, the first parameter of the callback returns error information, that is, throw an exception asynchronously.
        let e: BusinessError = error as BusinessError;
        console.error(`convertKey error, ${e.code}, ${e.message}`);
        return;
      }
      console.info('key algName: ' + key.algName);
      console.info('key format: ' + key.format);
      let encodedKey = key.getEncoded(); // Obtain the binary data of the symmetric key and output the data as a byte array. The length is 24 bytes.
      console.info('key getEncoded hex: ' + encodedKey.data);
    })
  } catch (error) {// Throw an exception immediately when an error is detected during parameter check.
    let e: BusinessError = error as BusinessError;
    console.error(`convertKey failed, ${e.code}, ${e.message}`);
  }
}

Converting Binary Data into an HMAC Key

For details about the algorithm specifications, see HMAC.

1. Obtain the HMAC binary key and encapsulate it into a DataBlob object.

2. Use cryptoFramework.createSymKeyGenerator with the string parameter 'HMAC' to create a symmetric key generator (SymKeyGenerator) object for an HMAC key of [1, 32768] bits.

3. Use SymKeyGenerator.convertKey to convert the binary data into a symmetric key (SymKey).

4. Use SymKey.getEncoded to obtain the binary data of the key.

Example: Convert binary data into an HMAC key in await mode.

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

async function testConvertHmacKey() {
  // The symmetric key length is 64 bytes and 512 bits.
  let keyMessage = '12345678abcdefgh12345678abcdefgh12345678abcdefgh12345678abcdefgh';
  let keyBlob: cryptoFramework.DataBlob = {
    data : new Uint8Array(buffer.from(keyMessage, 'utf-8').buffer)
  }
  let symKeyGenerator = cryptoFramework.createSymKeyGenerator('HMAC');
  let key = await symKeyGenerator.convertKey(keyBlob);
  let encodedKey = key.getEncoded();
  console.info('key encoded data: ' + encodedKey.data);
}