# suspicious-insecure-cipher-mode-usage (S305)#

Derived from the **flake8-bandit** linter.

## What it does#

Checks for uses of weak or broken cryptographic cipher modes.

## Why is this bad?#

Weak or broken cryptographic ciphers may be susceptible to attacks that allow an attacker to decrypt ciphertext without knowing the key or otherwise compromise the security of the cipher, such as forgeries.

Use strong, modern cryptographic ciphers instead of weak or broken ones.

## Example#

```
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
algorithm = algorithms.ARC4(key)
cipher = Cipher(algorithm, mode=modes.ECB(iv))
encryptor = cipher.encryptor()
```

Use instead:

```
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
algorithm = algorithms.ARC4(key)
cipher = Cipher(algorithm, mode=modes.CTR(iv))
encryptor = cipher.encryptor()
```