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#
# This file is part of pysnmp software.
#
# Copyright (c) 2005-2017, Ilya Etingof <etingof@gmail.com>
# License: http://snmplabs.com/pysnmp/license.html
#
import random
from pysnmp.proto.secmod.rfc3414.priv import base
from pysnmp.proto.secmod.rfc3414.auth import hmacmd5, hmacsha
from pysnmp.proto.secmod.rfc3414 import localkey
from pysnmp.proto.secmod.rfc7860.auth import hmacsha2
from pysnmp.proto import errind, error
from pyasn1.type import univ
from pyasn1.compat.octets import null
from math import ceil
try:
from hashlib import md5, sha1
except ImportError:
import md5
import sha
md5 = md5.new
sha1 = sha.new
try:
from Cryptodome.Cipher import DES3
except ImportError:
DES3 = None
random.seed()
# 5.1.1
class Des3(base.AbstractEncryptionService):
"""Reeder 3DES-EDE for USM (Internet draft).
https://tools.ietf.org/html/draft-reeder-snmpv3-usm-3desede-00
"""
serviceID = (1, 3, 6, 1, 6, 3, 10, 1, 2, 3) # usm3DESEDEPrivProtocol
keySize = 32
_localInt = random.randrange(0, 0xffffffff)
def hashPassphrase(self, authProtocol, privKey):
if authProtocol == hmacmd5.HmacMd5.serviceID:
hashAlgo = md5
elif authProtocol == hmacsha.HmacSha.serviceID:
hashAlgo = sha1
elif authProtocol in hmacsha2.HmacSha2.hashAlgorithms:
hashAlgo = hmacsha2.HmacSha2.hashAlgorithms[authProtocol]
else:
raise error.ProtocolError(
'Unknown auth protocol %s' % (authProtocol,)
)
return localkey.hashPassphrase(privKey, hashAlgo)
# 2.1
def localizeKey(self, authProtocol, privKey, snmpEngineID):
if authProtocol == hmacmd5.HmacMd5.serviceID:
hashAlgo = md5
elif authProtocol == hmacsha.HmacSha.serviceID:
hashAlgo = sha1
elif authProtocol in hmacsha2.HmacSha2.hashAlgorithms:
hashAlgo = hmacsha2.HmacSha2.hashAlgorithms[authProtocol]
else:
raise error.ProtocolError(
'Unknown auth protocol %s' % (authProtocol,)
)
localPrivKey = localkey.localizeKey(privKey, snmpEngineID, hashAlgo)
# now extend this key if too short by repeating steps that includes the hashPassphrase step
while len(localPrivKey) < self.keySize:
# this is the difference between reeder and bluementhal
newKey = localkey.hashPassphrase(localPrivKey, hashAlgo)
localPrivKey += localkey.localizeKey(newKey, snmpEngineID, hashAlgo)
return localPrivKey[:self.keySize]
# 5.1.1.1
def __getEncryptionKey(self, privKey, snmpEngineBoots):
# 5.1.1.1.1
des3Key = privKey[:24]
preIV = privKey[24:32]
securityEngineBoots = int(snmpEngineBoots)
salt = [
securityEngineBoots >> 24 & 0xff,
securityEngineBoots >> 16 & 0xff,
securityEngineBoots >> 8 & 0xff,
securityEngineBoots & 0xff,
self._localInt >> 24 & 0xff,
self._localInt >> 16 & 0xff,
self._localInt >> 8 & 0xff,
self._localInt & 0xff
]
if self._localInt == 0xffffffff:
self._localInt = 0
else:
self._localInt += 1
# salt not yet hashed XXX
return (des3Key.asOctets(),
univ.OctetString(salt).asOctets(),
univ.OctetString(map(lambda x, y: x ^ y, salt, preIV.asNumbers())).asOctets())
@staticmethod
def __getDecryptionKey(privKey, salt):
return (privKey[:24].asOctets(),
univ.OctetString(map(lambda x, y: x ^ y, salt.asNumbers(), privKey[24:32].asNumbers())).asOctets())
# 5.1.1.2
def encryptData(self, encryptKey, privParameters, dataToEncrypt):
if DES3 is None:
raise error.StatusInformation(
errorIndication=errind.encryptionError
)
snmpEngineBoots, snmpEngineTime, salt = privParameters
des3Key, salt, iv = self.__getEncryptionKey(
encryptKey, snmpEngineBoots
)
des3Obj = DES3.new(des3Key, DES3.MODE_CBC, iv)
privParameters = univ.OctetString(salt)
plaintext = dataToEncrypt + univ.OctetString((0,) * (8 - len(dataToEncrypt) % 8)).asOctets()
ciphertext = des3Obj.encrypt(plaintext)
return univ.OctetString(ciphertext), privParameters
# 5.1.1.3
def decryptData(self, decryptKey, privParameters, encryptedData):
if DES3 is None:
raise error.StatusInformation(
errorIndication=errind.decryptionError
)
snmpEngineBoots, snmpEngineTime, salt = privParameters
if len(salt) != 8:
raise error.StatusInformation(
errorIndication=errind.decryptionError
)
des3Key, iv = self.__getDecryptionKey(decryptKey, salt)
if len(encryptedData) % 8 != 0:
raise error.StatusInformation(
errorIndication=errind.decryptionError
)
des3Obj = DES3.new(des3Key, DES3.MODE_CBC, iv)
ciphertext = encryptedData.asOctets()
plaintext = des3Obj.decrypt(ciphertext)
return plaintext
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