#
# 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
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