#
# 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 hashlib import md5
from hashlib import sha1

try:
    from pysnmpcrypto import aes, PysnmpCryptoError

except ImportError:
    PysnmpCryptoError = AttributeError
    aes = None

from pyasn1.type import univ
from pysnmp.proto.secmod.rfc3414.priv import base
from pysnmp.proto.secmod.rfc3414.auth import hmacmd5
from pysnmp.proto.secmod.rfc3414.auth import hmacsha
from pysnmp.proto.secmod.rfc7860.auth import hmacsha2
from pysnmp.proto.secmod.rfc3414 import localkey
from pysnmp.proto import errind
from pysnmp.proto import error

random.seed()


# RFC3826

#

class Aes(base.AbstractEncryptionService):
    SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 2, 4)  # usmAesCfb128Protocol
    KEY_SIZE = 16

    local_int = random.randrange(0, 0xffffffffffffffff)

    # 3.1.2.1
    def __getEncryptionKey(self, privKey, snmpEngineBoots, snmpEngineTime):
        salt = [self.local_int >> 56 & 0xff,
                self.local_int >> 48 & 0xff,
                self.local_int >> 40 & 0xff,
                self.local_int >> 32 & 0xff,
                self.local_int >> 24 & 0xff,
                self.local_int >> 16 & 0xff,
                self.local_int >> 8 & 0xff,
                self.local_int & 0xff]

        if self.local_int == 0xffffffffffffffff:
            self.local_int = 0
        else:
            self.local_int += 1

        return self.__getDecryptionKey(privKey, snmpEngineBoots, snmpEngineTime, salt) + (
        univ.OctetString(salt).asOctets(),)

    def __getDecryptionKey(self, privKey, snmpEngineBoots,
                           snmpEngineTime, salt):
        snmpEngineBoots, snmpEngineTime, salt = (
            int(snmpEngineBoots), int(snmpEngineTime), salt
        )

        iv = [snmpEngineBoots >> 24 & 0xff,
              snmpEngineBoots >> 16 & 0xff,
              snmpEngineBoots >> 8 & 0xff,
              snmpEngineBoots & 0xff,
              snmpEngineTime >> 24 & 0xff,
              snmpEngineTime >> 16 & 0xff,
              snmpEngineTime >> 8 & 0xff,
              snmpEngineTime & 0xff] + salt

        return privKey[:self.KEY_SIZE].asOctets(), univ.OctetString(iv).asOctets()

    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)

    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)
        return localPrivKey[:self.KEY_SIZE]

    # 3.2.4.1
    def encryptData(self, encryptKey, privParameters, dataToEncrypt):
        snmpEngineBoots, snmpEngineTime, salt = privParameters

        # 3.3.1.1
        aesKey, iv, salt = self.__getEncryptionKey(
            encryptKey, snmpEngineBoots, snmpEngineTime
        )

        # 3.3.1.3
        # PyCrypto seems to require padding
        dataToEncrypt = dataToEncrypt + univ.OctetString((0,) * (16 - len(dataToEncrypt) % 16)).asOctets()

        try:
            ciphertext = aes.encrypt(dataToEncrypt, aesKey, iv)

        except PysnmpCryptoError:
            raise error.StatusInformation(
                errorIndication=errind.unsupportedPrivProtocol
            )

        # 3.3.1.4
        return univ.OctetString(ciphertext), univ.OctetString(salt)

    # 3.2.4.2
    def decryptData(self, decryptKey, privParameters, encryptedData):
        snmpEngineBoots, snmpEngineTime, salt = privParameters

        # 3.3.2.1
        if len(salt) != 8:
            raise error.StatusInformation(
                errorIndication=errind.decryptionError
            )

        # 3.3.2.3
        aesKey, iv = self.__getDecryptionKey(
            decryptKey, snmpEngineBoots, snmpEngineTime, salt
        )

        # PyCrypto seems to require padding
        encryptedData = encryptedData + univ.OctetString((0,) * (16 - len(encryptedData) % 16)).asOctets()

        try:
            # 3.3.2.4-6
            return aes.decrypt(encryptedData.asOctets(), aesKey, iv)

        except PysnmpCryptoError:
            raise error.StatusInformation(
                errorIndication=errind.unsupportedPrivProtocol
            )