CWE-325: Missing Cryptographic Step

What is Missing Cryptographic Step?

• Overview: This vulnerability occurs when a cryptographic algorithm lacks the implementation of a critical step, leading to encryption that is weaker than intended.

• Exploitation Methods:

• Attackers can analyze the incomplete encryption process to potentially decrypt data more easily than if the full algorithm was implemented.
• Common attack patterns include cryptanalysis techniques that take advantage of these missing steps to infer or reconstruct the original data.

• Security Impact:

• Direct consequences include reduced data confidentiality and integrity.
• Potential cascading effects may involve unauthorized data access and breach of sensitive information.
• Business impact could lead to loss of customer trust, legal ramifications, and financial damage due to data breaches.

• Prevention Guidelines:

• Specific code-level fixes include ensuring all steps of a cryptographic algorithm are correctly implemented as per the specification.
• Security best practices involve regular code reviews and testing for cryptographic compliance.
• Recommended tools and frameworks include using vetted cryptographic libraries and tools that abstract low-level cryptographic operations to reduce human error.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not Technology-Specific

Vulnerable Code Example

from Crypto.Cipher import AES
import os

def encrypt_data(plaintext, key):
    # Vulnerable: Missing Initialization Vector (IV)
    # In AES CBC mode, an IV is necessary to ensure that identical plaintext blocks
    # result in different ciphertexts, preventing patterns from being discerned.
    cipher = AES.new(key, AES.MODE_CBC)  # Missing IV parameter
    ciphertext = cipher.encrypt(plaintext)  # Encrypts plaintext directly
    return ciphertext

Explanation:

• The code above demonstrates a CWE-325: Missing Cryptographic Step vulnerability.
• The key issue is the absence of an Initialization Vector (IV) when using AES in CBC mode.
• AES in CBC mode requires an IV to ensure that identical plaintext blocks produce different ciphertexts, enhancing security by making the encryption non-deterministic.

How to fix Missing Cryptographic Step?

To fix this vulnerability, you must properly generate and use an Initialization Vector (IV) when encrypting data. The IV should be unique and random for each encryption operation. Typically, the IV is generated using a cryptographic random number generator and is the same block size as the cipher (e.g., 16 bytes for AES).

Steps:

1. Generate a secure, random IV for each encryption operation.
2. Prepend or append the IV to the ciphertext so it can be used during decryption.

Fixed Code Example

from Crypto.Cipher import AES
import os

def encrypt_data(plaintext, key):
    # Secure: Generate a random IV
    iv = os.urandom(16)  # AES block size is 16 bytes
    cipher = AES.new(key, AES.MODE_CBC, iv)  # Provide the IV to the cipher
    # Ensure plaintext is padded to a multiple of 16 bytes (AES block size)
    padded_plaintext = plaintext + b" " * (16 - len(plaintext) % 16)
    ciphertext = cipher.encrypt(padded_plaintext)
    
    # Return the IV alongside the ciphertext to use during decryption
    return iv + ciphertext

Explanation:

• Line 7: Generates a secure random IV using os.urandom(16) to ensure it is cryptographically secure.
• Line 8: Passes the IV to the AES cipher initialization.
• Line 10: Ensures that the plaintext is padded to the AES block size (16 bytes) to prevent errors during encryption.
• Line 14: Combines the IV with the ciphertext to ensure the IV is available for decryption.

By addressing the missing cryptographic step, the encryption process becomes more secure, mitigating the risk of predictable output from similar plaintext inputs.