# python.pycryptodome.security.insecure-cipher-algorithm-rc4.insecure-cipher-algorithm-rc4

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Detected ARC4 cipher algorithm which is considered insecure. This algorithm is not cryptographically secure and can be reversed easily. Use AES instead.

## Run Locally

## Run in CI

## Defintion

```
rules:
- id: insecure-cipher-algorithm-rc4
message: Detected ARC4 cipher algorithm which is considered insecure. This
algorithm is not cryptographically secure and can be reversed easily. Use
AES instead.
metadata:
source-rule-url: https://github.com/PyCQA/bandit/blob/d5f8fa0d89d7b11442fc6ec80ca42953974354c8/bandit/blacklists/calls.py#L84
cwe:
- "CWE-327: Use of a Broken or Risky Cryptographic Algorithm"
owasp:
- A03:2017 - Sensitive Data Exposure
- A02:2021 - Cryptographic Failures
bandit-code: B304
references:
- https://cwe.mitre.org/data/definitions/326.html
category: security
technology:
- pycryptodome
subcategory:
- vuln
likelihood: LOW
impact: MEDIUM
confidence: MEDIUM
license: Commons Clause License Condition v1.0[LGPL-2.1-only]
vulnerability_class:
- Cryptographic Issues
severity: WARNING
languages:
- python
pattern-either:
- pattern: Cryptodome.Cipher.ARC4.new(...)
- pattern: Crypto.Cipher.ARC4.new(...)
```

### Examples

#### insecure-cipher-algorithm-rc4.py

```
# cf. https://github.com/PyCQA/bandit/blob/b78c938c0bd03d201932570f5e054261e10c5750/examples/ciphers.py
from Crypto.Cipher import AES
from Crypto.Cipher import ARC2 as pycrypto_arc2
from Crypto.Cipher import ARC4 as pycrypto_arc4
from Crypto.Cipher import Blowfish as pycrypto_blowfish
from Crypto.Cipher import DES as pycrypto_des
from Crypto.Cipher import XOR as pycrypto_xor
from Cryptodome.Cipher import ARC2 as pycryptodomex_arc2
from Cryptodome.Cipher import ARC4 as pycryptodomex_arc4
from Cryptodome.Cipher import Blowfish as pycryptodomex_blowfish
from Cryptodome.Cipher import DES as pycryptodomex_des
from Cryptodome.Cipher import XOR as pycryptodomex_xor
from Crypto.Hash import SHA
from Crypto import Random
from Crypto.Util import Counter
key = b'Very long and confidential key'
nonce = Random.new().read(16)
tempkey = SHA.new(key+nonce).digest()
# ruleid:insecure-cipher-algorithm-rc4
cipher = pycrypto_arc4.new(tempkey)
msg = nonce + cipher.encrypt(b'Open the pod bay doors, HAL')
# ruleid:insecure-cipher-algorithm-rc4
cipher = pycryptodomex_arc4.new(tempkey)
msg = nonce + cipher.encrypt(b'Open the pod bay doors, HAL')
# ok:insecure-cipher-algorithm-rc4
cipher = AES.new(key, AES.MODE_EAX, nonce=nonce)
plaintext = cipher.decrypt(ciphertext)
try:
cipher.verify(tag)
print("The message is authentic:", plaintext)
except ValueError:
print("Key incorrect or message corrupted")
```

Short Link: https://sg.run/Eo6N