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SM4 Encryption-Decryption CTR Block Mode Fails with IVParamsSpec Parameter.

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Read the original article：SM4 Encryption-Decryption CTR Block Mode Fails with IVParamsSpec Parameter.

SM4 Encryption-Decryption CTR Block Mode Fails with IVParamsSpec Parameter.

Problem Description

An error occurs when using the SM4 encryption/decryption algorithm with the CTR block mode after adding the IVParamsSpec parameter.

Encryption/Decryption Code (ArkTS):

// Encrypt message.  
async function encryptMessagePromise(symKey: cryptoFramework.SymKey, plainText: cryptoFramework.DataBlob) {  
  let cipher = cryptoFramework.createCipher('SM4_128|CTR|NoPadding');  
  let smIV = '12345678';  
  let ivParamsSpec: cryptoFramework.IvParamsSpec = {  
    algName: "IvParamsSpec",  
    iv: { data: new Uint8Array(buffer.from(smIV, 'utf-8').buffer) }  
  };  
  await cipher.init(cryptoFramework.CryptoMode.ENCRYPT_MODE, symKey, ivParamsSpec);  
  let encryptData = await cipher.doFinal(plainText);  
  return encryptData;  
}  

// Decrypt message.  
async function decryptMessagePromise(symKey: cryptoFramework.SymKey, cipherText: cryptoFramework.DataBlob) {  
  let decoder = cryptoFramework.createCipher('SM4_128|CTR|NoPadding');  
  let smIV = '12345678';  
  let ivParamsSpec: cryptoFramework.IvParamsSpec = {  
    algName: "IvParamsSpec",  
    iv: { data: new Uint8Array(buffer.from(smIV, 'utf-8').buffer) }  
  };  
  await decoder.init(cryptoFramework.CryptoMode.DECRYPT_MODE, symKey, ivParamsSpec);  
  let decryptData = await decoder.doFinal(cipherText);  
  return decryptData;  
}
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Error Message:

decrypt ok enData: VLhJHQ==  
decrypt ok deDate: ��G  
decrypt failed
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Background Knowledge

The algorithm library currently provides 7 common encryption modes for SM4: ECB, CBC, CTR, OFB, CFB, CFB128, and GCM. Different encryption modes require specific parameters. For details, refer to ParamsSpec.

Troubleshooting Process

  1. Check if the parameters passed when creating the encryption/decryption instance are correct.
  2. Check if the parameters passed during the init method of the encryption/decryption instance are correct.
  3. Verify if the IVParamsSpec parameter meets the requirements.

Analysis Conclusion

The IVParamsSpec parameter provided is 8 bytes long, but the IVParamsSpec parameter for encryption/decryption requires 16 bytes. The incorrect length of the IVParamsSpec parameter causes the encryption/decryption failure.

Solution

Update the IVParamsSpec initialization to use a 16-byte IV instead of 8 bytes. For example:

let smIV = '1234567890123456'; // 16-byte IV
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Verification Result

After updating the IVParamsSpec to use a 16-byte IV instead of the previous 8-byte string, the encryption and decryption processes were re-executed.

  • Before fix:
    • Encryption succeeded.
    • Decryption produced corrupted output and failed validation.
  • After fix:
    • Encryption succeeded with no error.
    • Decryption successfully restored the original plaintext message.
    • No error message occurred during the process.

Related Documents or Links

https://developer.huawei.com/consumer/en/doc/harmonyos-references/js-apis-cryptoframework#ivparamsspec

Written by Mehmet Algul

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