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#
# This file is part of pysnmp software.
#
# Copyright (c) 2005-2019, Ilya Etingof <etingof@gmail.com>
# License: http://snmplabs.com/pysnmp/license.html
#
import random
try:
from hashlib import md5, sha1
except ImportError:
import md5
import sha
md5 = md5.new
sha1 = sha.new
try:
from pysnmpcrypto import des3, PysnmpCryptoError
except ImportError:
PysnmpCryptoError = AttributeError
des3 = None
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
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
"""
SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 2, 3) # usm3DESEDEPrivProtocol
KEY_SIZE = 32
local_int = random.randrange(0, 0xffffffff)
def hashPassphrase(self, authProtocol, privKey):
if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
hashAlgo = md5
elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
hashAlgo = sha1
elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[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.SERVICE_ID:
hashAlgo = md5
elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
hashAlgo = sha1
elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[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.KEY_SIZE:
# this is the difference between reeder and bluementhal
newKey = localkey.hashPassphrase(localPrivKey, hashAlgo)
localPrivKey += localkey.localizeKey(newKey, snmpEngineID, hashAlgo)
return localPrivKey[:self.KEY_SIZE]
# 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.local_int >> 24 & 0xff,
self.local_int >> 16 & 0xff,
self.local_int >> 8 & 0xff,
self.local_int & 0xff
]
if self.local_int == 0xffffffff:
self.local_int = 0
else:
self.local_int += 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):
snmpEngineBoots, snmpEngineTime, salt = privParameters
des3Key, salt, iv = self.__getEncryptionKey(
encryptKey, snmpEngineBoots
)
privParameters = univ.OctetString(salt)
plaintext = dataToEncrypt + univ.OctetString((0,) * (8 - len(dataToEncrypt) % 8)).asOctets()
try:
ciphertext = des3.encrypt(plaintext, des3Key, iv)
except PysnmpCryptoError:
raise error.StatusInformation(
errorIndication=errind.unsupportedPrivProtocol
)
return univ.OctetString(ciphertext), privParameters
# 5.1.1.3
def decryptData(self, decryptKey, privParameters, encryptedData):
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
)
ciphertext = encryptedData.asOctets()
try:
plaintext = des3.decrypt(ciphertext, des3Key, iv)
except PysnmpCryptoError:
raise error.StatusInformation(
errorIndication=errind.unsupportedPrivProtocol
)
return plaintext
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