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Use of a broken or weak cryptographic algorithm

ID: py/weak-cryptographic-algorithm
Kind: problem
Severity: warning
Precision: high
Tags:
   - security
   - external/cwe/cwe-327
Query suites:
   - python-code-scanning.qls
   - python-security-extended.qls
   - python-security-and-quality.qls

Click to see the query in the CodeQL repository

Using broken or weak cryptographic algorithms can leave data vulnerable to being decrypted or forged by an attacker.

Many cryptographic algorithms provided by cryptography libraries are known to be weak, or flawed. Using such an algorithm means that encrypted or hashed data is less secure than it appears to be.

This query alerts on any use of a weak cryptographic algorithm, that is not a hashing algorithm. Use of broken or weak cryptographic hash functions are handled by the py/weak-sensitive-data-hashing query.

Recommendation

Ensure that you use a strong, modern cryptographic algorithm, such as AES-128 or RSA-2048.

Example

The following code uses the pycryptodome library to encrypt some secret data. When you create a cipher using pycryptodome you must specify the encryption algorithm to use. The first example uses DES, which is an older algorithm that is now considered weak. The second example uses AES, which is a stronger modern algorithm.

from Crypto.Cipher import DES, AES

cipher = DES.new(SECRET_KEY)

def send_encrypted(channel, message):
    channel.send(cipher.encrypt(message)) # BAD: weak encryption


cipher = AES.new(SECRET_KEY)

def send_encrypted(channel, message):
    channel.send(cipher.encrypt(message)) # GOOD: strong encryption

NOTICE: the original [pycrypto](https://pypi.org/project/pycrypto/) PyPI package that provided the Crypto module is not longer actively maintained, so you should use the [pycryptodome](https://pypi.org/project/pycryptodome/) PyPI package instead (which has a compatible API).

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