rspec/rules/S5547/python/rule.adoc

include::../description.adoc[]

== Noncompliant Code Example

https://pycryptodome.readthedocs.io[pycryptodomex] library:

----
from Cryptodome.Cipher import DES, DES3, ARC2, ARC4, Blowfish, AES
from Cryptodome.Random import get_random_bytes

key = b'-8B key-'
DES.new(key, DES.MODE_OFB) # Noncompliant: DES works with 56-bit keys allow attacks via exhaustive search

key = DES3.adjust_key_parity(get_random_bytes(24))
cipher = DES3.new(key, DES3.MODE_CFB) # Noncompliant: Triple DES is vulnerable to meet-in-the-middle attack

key = b'Sixteen byte key'
cipher = ARC2.new(key, ARC2.MODE_CFB) # Noncompliant: RC2 is vulnerable to a related-key attack

key = b'Very long and confidential key'
cipher = ARC4.new(key) # Noncompliant: vulnerable to several attacks (see https://en.wikipedia.org/wiki/RC4#Security)

key = b'An arbitrarily long key'
cipher = Blowfish.new(key, Blowfish.MODE_CBC) # Noncompliant: Blowfish use a 64-bit block size makes it vulnerable to birthday attacks
----

https://pycryptodome.readthedocs.io[pycryptodome] library:

----
from Crypto.Cipher import DES, DES3, ARC2, ARC4, Blowfish, AES
from Crypto.Random import get_random_bytes

key = b'-8B key-'
DES.new(key, DES.MODE_OFB) # Noncompliant: DES works with 56-bit keys allow attacks via exhaustive search

key = DES3.adjust_key_parity(get_random_bytes(24))
cipher = DES3.new(key, DES3.MODE_CFB) # Noncompliant: Triple DES is vulnerable to meet-in-the-middle attack

key = b'Sixteen byte key'
cipher = ARC2.new(key, ARC2.MODE_CFB) # Noncompliant: RC2 is vulnerable to a related-key attack

key = b'Very long and confidential key'
cipher = ARC4.new(key) # Noncompliant: vulnerable to several attacks (see https://en.wikipedia.org/wiki/RC4#Security)

key = b'An arbitrarily long key'
cipher = Blowfish.new(key, Blowfish.MODE_CBC) # Noncompliant: Blowfish use a 64-bit block size makes it vulnerable to birthday attacks
----

https://cryptography.io/en/latest/[pyca] library:

----
import os
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.backends import default_backend

key = os.urandom(16)
iv = os.urandom(16)

tdes4 = Cipher(algorithms.TripleDES(key), mode=None, backend=default_backend()) # Noncompliant: Triple DES is vulnerable to meet-in-the-middle attack
bf3 = Cipher(algorithms.Blowfish(key), mode=None, backend=default_backend()) # Noncompliant: Blowfish use a 64-bit block size makes it vulnerable to birthday attacks
rc42 = Cipher(algorithms.ARC4(key), mode=None, backend=default_backend()) # Noncompliant: vulnerable to several attacks (see https://en.wikipedia.org/wiki/RC4#Security)
----

https://pypi.org/project/pyDes/[pydes] library:

----
import pyDes;

des1 = pyDes.des('ChangeIt')  # Noncompliant: DES works with 56-bit keys allow attacks via exhaustive search
des2 = pyDes.des('ChangeIt', pyDes.CBC, "\0\0\0\0\0\0\0\0", pad=None, padmode=pyDes.PAD_PKCS5) # Noncompliant: DES works with 56-bit keys allow attacks via exhaustive search

tdes1 = pyDes.triple_des('ChangeItWithYourKey!!!!!')  # Noncompliant: Triple DES is vulnerable to meet-in-the-middle attack
tdes2 = pyDes.triple_des('ChangeItWithYourKey!!!!!', pyDes.CBC, "\0\0\0\0\0\0\0\0", pad=None, padmode=pyDes.PAD_PKCS5) # Noncompliant: Triple DES is vulnerable to meet-in-the-middle attack
----

https://pycrypto.readthedocs.io/en/latest/[pycrypto] library is not maintained and therefore should not be used:

----
from Crypto.Cipher import *

des3 = DES.new('ChangeIt') # Noncompliant: DES works with 56-bit keys allow attacks via exhaustive search
tdes3 = DES3.new('ChangeItChangeIt') # Noncompliant: Triple DES is vulnerable to meet-in-the-middle attack
bf2 = Blowfish.new('ChangeItWithYourKey', Blowfish.MODE_CBC, 'ChangeIt') # Noncompliant: Blowfish use a 64-bit block size makes it
rc21 = ARC2.new('ChangeItWithYourKey', ARC2.MODE_CFB, 'ChangeIt') # Noncompliant: RC2 is vulnerable to a related-key attack
rc41 = ARC4.new('ChangeItWithYourKey') # Noncompliant: vulnerable to several attacks (see https://en.wikipedia.org/wiki/RC4#Security)
----

== Compliant Solution

https://pycryptodome.readthedocs.io[pycryptodomex] library:

----
from Cryptodome.Cipher import AES

key = b'Sixteen byte key'
cipher = AES.new(key, AES.MODE_CCM) # Compliant
----

https://pycryptodome.readthedocs.io[pycryptodome] library:

----
from Crypto.Cipher import AES

key = b'Sixteen byte key'
cipher = AES.new(key, AES.MODE_CCM) # Compliant
----

https://cryptography.io/en/latest/[pyca] library:

----
import os
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.backends import default_backend

key = os.urandom(16)
iv = os.urandom(16)

aes2 = Cipher(algorithms.AES(key), modes.CBC(iv), backend=default_backend()) # Compliant
----

https://pycrypto.readthedocs.io/en/latest/[pycrypto] library is not maintained and therefore should not be used:

----
from Crypto.Cipher import *

aes1 = AES.new('This is a key123', AES.MODE_CBC, 'This is an IV456') # Compliant
----

include::../see.adoc[]

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== Comments And Links
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