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"""
Crypto logic for RFC3414.
https://tools.ietf.org/html/rfc3414
"""
from pysnmp.crypto import backend, CRYPTODOME, CRYPTOGRPAHY, des3, generic_decrypt, generic_encrypt
if backend == CRYPTODOME:
from Cryptodome.Cipher import DES
def _cryptodome_cipher(key, iv):
"""Build a Pycryptodome DES Cipher object.
:param bytes key: Encryption key
:param bytes IV: Initialization vector
:returns: DES Cipher instance
"""
return DES.new(key, DES.MODE_CBC, iv)
_CIPHER_FACTORY_MAP = {
CRYPTODOME: _cryptodome_cipher
}
# Cryptography does not support DES directly because it is a seriously old, insecure,
# and deprecated algorithm. However, triple DES is just three rounds of DES (encrypt,
# decrypt, encrypt) done by taking a key three times the size of a DES key and breaking
# it into three pieces. So triple DES with des_key * 3 is equivalent to DES.
# Pycryptodome's triple DES implementation will actually throw an error if it receives
# a key that reduces to DES.
def encrypt(plaintext, key, iv):
"""Encrypt data using DES on the available backend.
:param bytes plaintext: Plaintext data to encrypt
:param bytes key: Encryption key
:param bytes IV: Initialization vector
:returns: Encrypted ciphertext
:rtype: bytes
"""
if backend == CRYPTOGRPAHY:
return des3.encrypt(plaintext, key * 3, iv)
return generic_encrypt(_CIPHER_FACTORY_MAP, plaintext, key, iv)
def decrypt(ciphertext, key, iv):
"""Decrypt data using DES on the available backend.
:param bytes ciphertext: Ciphertext data to decrypt
:param bytes key: Encryption key
:param bytes IV: Initialization vector
:returns: Decrypted plaintext
:rtype: bytes
"""
if backend == CRYPTOGRPAHY:
return des3.decrypt(ciphertext, key * 3, iv)
return generic_decrypt(_CIPHER_FACTORY_MAP, ciphertext, key, iv)
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