155 lines
4.9 KiB
Python
155 lines
4.9 KiB
Python
#
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# This file is part of pysnmp software.
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#
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# Copyright (c) 2005-2017, Ilya Etingof <etingof@gmail.com>
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# License: http://pysnmp.sf.net/license.html
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#
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import random
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from pysnmp.proto.secmod.rfc3414.priv import base
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from pysnmp.proto.secmod.rfc3414.auth import hmacmd5, hmacsha
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from pysnmp.proto.secmod.rfc3414 import localkey
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from pysnmp.proto import errind, error
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from pyasn1.type import univ
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from pyasn1.compat.octets import null
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from math import ceil
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try:
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from hashlib import md5, sha1
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except ImportError:
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import md5
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import sha
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md5 = md5.new
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sha1 = sha.new
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try:
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from Crypto.Cipher import DES3
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except ImportError:
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DES3 = None
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random.seed()
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# 5.1.1
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class Des3(base.AbstractEncryptionService):
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"""Reeder 3DES-EDE for USM (Internet draft).
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https://tools.ietf.org/html/draft-reeder-snmpv3-usm-3desede-00
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"""
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serviceID = (1, 3, 6, 1, 6, 3, 10, 1, 2, 3) # usm3DESEDEPrivProtocol
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keySize = 32
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_localInt = random.randrange(0, 0xffffffff)
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def hashPassphrase(self, authProtocol, privKey):
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if authProtocol == hmacmd5.HmacMd5.serviceID:
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return localkey.hashPassphraseMD5(privKey)
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elif authProtocol == hmacsha.HmacSha.serviceID:
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return localkey.hashPassphraseSHA(privKey)
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else:
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raise error.ProtocolError(
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'Unknown auth protocol %s' % (authProtocol,)
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)
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# 2.1
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def localizeKey(self, authProtocol, privKey, snmpEngineID):
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if authProtocol == hmacmd5.HmacMd5.serviceID:
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localPrivKey = localkey.localizeKeyMD5(privKey, snmpEngineID)
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# now extend this key if too short by repeating steps that includes the hashPassphrase step
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while len(localPrivKey) < self.keySize:
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newKey = localkey.hashPassphraseMD5(localPrivKey)
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localPrivKey += localkey.localizeKeyMD5(newKey, snmpEngineID)
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elif authProtocol == hmacsha.HmacSha.serviceID:
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localPrivKey = localkey.localizeKeySHA(privKey, snmpEngineID)
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while len(localPrivKey) < self.keySize:
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newKey = localkey.hashPassphraseSHA(localPrivKey)
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localPrivKey += localkey.localizeKeySHA(newKey, snmpEngineID)
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else:
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raise error.ProtocolError(
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'Unknown auth protocol %s' % (authProtocol,)
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)
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return localPrivKey[:self.keySize]
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# 5.1.1.1
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def __getEncryptionKey(self, privKey, snmpEngineBoots):
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# 5.1.1.1.1
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des3Key = privKey[:24]
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preIV = privKey[24:32]
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securityEngineBoots = int(snmpEngineBoots)
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salt = [
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securityEngineBoots >> 24 & 0xff,
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securityEngineBoots >> 16 & 0xff,
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securityEngineBoots >> 8 & 0xff,
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securityEngineBoots & 0xff,
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self._localInt >> 24 & 0xff,
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self._localInt >> 16 & 0xff,
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self._localInt >> 8 & 0xff,
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self._localInt & 0xff
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]
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if self._localInt == 0xffffffff:
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self._localInt = 0
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else:
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self._localInt += 1
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# salt not yet hashed XXX
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return (des3Key.asOctets(),
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univ.OctetString(salt).asOctets(),
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univ.OctetString(map(lambda x, y: x ^ y, salt, preIV.asNumbers())).asOctets())
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@staticmethod
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def __getDecryptionKey(privKey, salt):
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return (privKey[:24].asOctets(),
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univ.OctetString(map(lambda x, y: x ^ y, salt.asNumbers(), privKey[24:32].asNumbers())).asOctets())
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# 5.1.1.2
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def encryptData(self, encryptKey, privParameters, dataToEncrypt):
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if DES3 is None:
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raise error.StatusInformation(
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errorIndication=errind.encryptionError
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)
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snmpEngineBoots, snmpEngineTime, salt = privParameters
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des3Key, salt, iv = self.__getEncryptionKey(
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encryptKey, snmpEngineBoots
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)
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des3Obj = DES3.new(des3Key, DES3.MODE_CBC, iv)
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privParameters = univ.OctetString(salt)
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plaintext = dataToEncrypt + univ.OctetString((0,) * (8 - len(dataToEncrypt) % 8)).asOctets()
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ciphertext = des3Obj.encrypt(plaintext)
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return univ.OctetString(ciphertext), privParameters
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# 5.1.1.3
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def decryptData(self, decryptKey, privParameters, encryptedData):
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if DES3 is None:
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raise error.StatusInformation(
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errorIndication=errind.decryptionError
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)
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snmpEngineBoots, snmpEngineTime, salt = privParameters
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if len(salt) != 8:
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raise error.StatusInformation(
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errorIndication=errind.decryptionError
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)
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des3Key, iv = self.__getDecryptionKey(decryptKey, salt)
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if len(encryptedData) % 8 != 0:
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raise error.StatusInformation(
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errorIndication=errind.decryptionError
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)
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des3Obj = DES3.new(des3Key, DES3.MODE_CBC, iv)
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ciphertext = encryptedData.asOctets()
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plaintext = des3Obj.decrypt(ciphertext)
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return plaintext
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