Description

This vulnerability detector identifies cryptographic functions that derive initialization vectors (IVs) or nonces from encryption keys. Using key-derived IVs/nonces is a cryptographic weakness that can lead to predictable encryption patterns and potential data exposure, as the same key will always produce the same IV/nonce, compromising the randomness required for secure encryption.

Detection Strategy

• The method first checks if any Python cryptographic libraries (such as Crypto, cryptography, or similar packages) are imported in the code

• It then examines function calls within the imported cryptographic libraries

• For each function call, it analyzes whether the call represents an encryption operation where the initialization vector (IV) or nonce parameter is derived from the encryption key

• A vulnerability is reported when an encryption function call uses a key-derived value for its IV or nonce parameter instead of using a properly random or unique value

Vulnerable code example

from Crypto.Cipher import AES

def encrypt_data(data):
    key = b'0123456789ABCDEF'  # 16-byte key
    
    # VULNERABLE: IV reuses the same bytes as the encryption key
    cipher = AES.new(key, AES.MODE_CBC, key)
    return cipher.encrypt(data)

✅ Secure code example

from Crypto.Cipher import AES
from Crypto.Random import get_random_bytes

def encrypt_data(data):
    key = b'0123456789ABCDEF'  # 16-byte key
    
    # SAFE: IV is generated randomly, not reused from key
    iv = get_random_bytes(16)...