Encryption algorithms should use secure modes and padding schemes where appropriate to guarantee data confidentiality and integrity.

• For block cipher encryption algorithms (like AES):
  • The ECB (Electronic Codebook) cipher mode doesn’t provide serious message confidentiality: under a given key any given plaintext block always gets encrypted to the same ciphertext block. This mode should never be used.
  • The CBC (Cipher Block Chaining) mode by itself provides only data confidentiality. This cipher mode is also vulnerable to padding oracle attacks when used with padding. Using CBC along with Message Authentication Code can provide data integrity and should prevent such attacks. In practice the implementation has many pitfalls and it’s recommended to avoid CBC with padding completely.
  • The GCM (Galois Counter Mode) mode which works internally with zero/no padding scheme, is recommended, as it is designed to provide both data authenticity (integrity) and confidentiality. Other similar modes are CCM, CWC, EAX, IAPM and OCB.
• For RSA encryption algorithm, the recommended padding scheme is OAEP.

Noncompliant Code Example

AesManaged object with insecure mode:

AesManaged aes4 = new AesManaged
{
  KeySize = 128,
  BlockSize = 128,
  Mode = CipherMode.ECB, // Noncompliant
  Padding = PaddingMode.PKCS7
};

RSACryptoServiceProvider object without OAEP padding:

RSACryptoServiceProvider RSA1 = new RSACryptoServiceProvider();
encryptedData = RSA1.Encrypt(dataToEncrypt, false); // Noncompliant: OAEP Padding is not used (second parameter set to false)

Compliant Solution

AES with GCM mode with bouncycastle library:

GcmBlockCipher blockCipher = new GcmBlockCipher(new AesEngine()); // Compliant
blockCipher.Init(true, new AeadParameters(new KeyParameter(secretKey), 128, iv, null));

AES with GCM mode with AesGcm object:

var aesGcm = new AesGcm(key); // Compliant

RSA with OAEP padding with RSACryptoServiceProvider object:

RSACryptoServiceProvider RSA2 = new RSACryptoServiceProvider();
encryptedData = RSA2.Encrypt(dataToEncrypt, true); // Compliant: OAEP Padding is used (second parameter set to true)

See

• OWASP Top 10 2021 Category A2 - Cryptographic Failures
• OWASP Top 10 2017 Category A6 - Security Misconfiguration
• MITRE, CWE-327 - Use of a Broken or Risky Cryptographic Algorithm
• SANS Top 25 - Porous Defenses