Skip to main content

Insecure encryption algorithm

Need​

Implementation of secure encryption algorithms

Context​

  • Usage of C# for developing robust and efficient applications
  • Usage of System.Security.Cryptography for secure data encryption and decryption

Description​

Non compliant code​

public string EncryptData(string data)
{
    string key = "b14ca5898a4e4133bbce2ea2315a1916";
    MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
    UTF8Encoding utf8 = new UTF8Encoding();
    TripleDESCryptoServiceProvider tDes = new TripleDESCryptoServiceProvider();

    tDes.Key = md5.ComputeHash(utf8.GetBytes(key));
    tDes.Mode = CipherMode.ECB;
    tDes.Padding = PaddingMode.PKCS7;

    byte[] dataBytes = utf8.GetBytes(data);
    ICryptoTransform transform = tDes.CreateEncryptor();
    byte[] encryptedBytes = transform.TransformFinalBlock(dataBytes, 0, dataBytes.Length);

    return Convert.ToBase64String(encryptedBytes);
}

In the provided code snippet, the application is using the MD5 hashing algorithm to create a hash of a given key, which is then used as the key for the Triple DES encryption algorithm.

MD5 is considered insecure because it is vulnerable to hash collisions, where different inputs can produce the same hash output. This makes it possible for an attacker to reverse-engineer the key from the hash, or to find another key that produces the same hash.

Triple DES (3DES) is also considered insecure for modern applications. It has a relatively small block size, which makes it vulnerable to certain types of attacks (like the Sweet32 attack). Furthermore, 3DES is significantly slower than more modern encryption algorithms.

The encryption mode used here is ECB (Electronic Codebook), which is the simplest form of encryption. It divides the input into blocks and encrypts each block separately. This can lead to patterns in the encrypted data, which can reveal information about the original data.

The padding mode used is PKCS7, which is secure when used correctly. However, it can be vulnerable to padding oracle attacks if not properly implemented.

Overall, this encryption method is not secure and should be replaced with a more secure encryption algorithm, such as AES. The key should be generated securely and not be based on an insecure hash like MD5. The encryption mode should also be changed from ECB to a more secure mode, like CBC or GCM.

Steps​

  • Replace the use of insecure encryption algorithm with a secure one.
  • Use a strong and secure encryption algorithm such as AES (Advanced Encryption Standard).
  • Ensure that the encryption algorithm supports secure key sizes and modes of operation.
  • Generate a secure and random encryption key.
  • Use a secure key management system to store and protect the encryption key.
  • Implement proper key management practices, such as key rotation and revocation.
  • Ensure that the encryption algorithm is properly configured with secure padding and mode of operation.
  • Test the encryption functionality to ensure it is working correctly and securely.

Compliant code​

public string EncryptData(string data)
{
    // Define the secret key. Use a secure method to store this.
    string key = "b14ca5898a4e4133bbce2ea2315a1916"; 

    // Convert the key to bytes and get the length.
    byte[] keyBytes = Encoding.UTF8.GetBytes(key);
    int keySize = keyBytes.Length * 8;

    // Create a new instance of the AesCryptoServiceProvider class.
    AesCryptoServiceProvider aes = new AesCryptoServiceProvider();

    // Configure the AES algorithm.
    aes.KeySize = keySize;
    aes.Key = keyBytes;
    aes.Mode = CipherMode.CBC;
    aes.Padding = PaddingMode.PKCS7;

    // Convert the data to bytes.
    byte[] dataBytes = Encoding.UTF8.GetBytes(data);

    // Create an encryptor and perform the encryption.
    ICryptoTransform encryptor = aes.CreateEncryptor();
    byte[] encryptedBytes = encryptor.TransformFinalBlock(dataBytes, 0, dataBytes.Length);

    // Convert the encrypted bytes back to a string and return it.
    return Convert.ToBase64String(encryptedBytes);
}

The above code fixes the vulnerability by replacing the insecure MD5 and TripleDES encryption algorithms with the secure AES encryption algorithm.

The AES algorithm is configured with a key size equal to the length of the secret key, a mode of operation of CBC (Cipher Block Chaining), and a padding mode of PKCS7.

The data to be encrypted is converted to bytes, encrypted using the AES algorithm, and then converted back to a string in Base64 format.

The secret key is currently hardcoded in the code, which is not secure. In a real-world application, you should use a secure method to store the secret key, such as a secure key vault.

You should also implement proper key management practices, such as key rotation and revocation, to further enhance the security of your encryption functionality.

Finally, you should test the encryption functionality to ensure it is working correctly and securely.

References​

Last updated on