rhodecode/lib/encrypt.py

# Copyright (C) 2014-2020 RhodeCode GmbH
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License, version 3
# (only), as published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
# This program is dual-licensed. If you wish to learn more about the
# RhodeCode Enterprise Edition, including its added features, Support services,
# and proprietary license terms, please see https://rhodecode.com/licenses/


"""
Generic encryption library for RhodeCode
"""

import base64
import logging

from Crypto.Cipher import AES
from Crypto import Random
from Crypto.Hash import HMAC, SHA256

from rhodecode.lib.str_utils import safe_bytes, safe_str
from rhodecode.lib.exceptions import signature_verification_error


class InvalidDecryptedValue(str):

    def __new__(cls, content):
        """
        This will generate something like this::
            <InvalidDecryptedValue(QkWusFgLJXR6m42v...)>
        And represent a safe indicator that encryption key is broken
        """
        content = '<{}({}...)>'.format(cls.__name__, content[:16])
        return str.__new__(cls, content)

KEY_FORMAT = b'enc$aes_hmac${1}'


class AESCipher(object):

    def __init__(self, key: bytes, hmac=False, strict_verification=True):

        if not key:
            raise ValueError('passed key variable is empty')
        self.strict_verification = strict_verification
        self.block_size = 32
        self.hmac_size = 32
        self.hmac = hmac

        self.key = SHA256.new(safe_bytes(key)).digest()
        self.hmac_key = SHA256.new(self.key).digest()

    def verify_hmac_signature(self, raw_data):
        org_hmac_signature = raw_data[-self.hmac_size:]
        data_without_sig = raw_data[:-self.hmac_size]
        recomputed_hmac = HMAC.new(
            self.hmac_key, data_without_sig, digestmod=SHA256).digest()
        return org_hmac_signature == recomputed_hmac

    def encrypt(self, raw: bytes):
        raw = self._pad(raw)
        iv = Random.new().read(AES.block_size)
        cipher = AES.new(self.key, AES.MODE_CBC, iv)
        enc_value = cipher.encrypt(raw)

        hmac_signature = b''
        if self.hmac:
            # compute hmac+sha256 on iv + enc text, we use
            # encrypt then mac method to create the signature
            hmac_signature = HMAC.new(
                self.hmac_key, iv + enc_value, digestmod=SHA256).digest()

        return base64.b64encode(iv + enc_value + hmac_signature)

    def decrypt(self, enc, safe=True) -> bytes | InvalidDecryptedValue:
        enc_org = enc
        try:
            enc = base64.b64decode(enc)
        except Exception:
            logging.exception('Failed Base64 decode')
            raise signature_verification_error('Failed Base64 decode')

        if self.hmac and len(enc) > self.hmac_size:
            if self.verify_hmac_signature(enc):
                # cut off the HMAC verification digest
                enc = enc[:-self.hmac_size]
            else:

                decrypt_fail = InvalidDecryptedValue(safe_str(enc_org))
                if safe:
                    return decrypt_fail
                raise signature_verification_error(decrypt_fail)

        iv = enc[:AES.block_size]
        cipher = AES.new(self.key, AES.MODE_CBC, iv)
        return self._unpad(cipher.decrypt(enc[AES.block_size:]))

    def _pad(self, s):
        block_pad = (self.block_size - len(s) % self.block_size)
        return s + block_pad * safe_bytes(chr(block_pad))

    @staticmethod
    def _unpad(s):
        return s[:-ord(s[len(s)-1:])]


def validate_and_decrypt_data(enc_data, enc_key, enc_strict_mode=False, safe=True):
    enc_data = safe_str(enc_data)

    parts = enc_data.split('$', 3)
    if len(parts) != 3:
        raise ValueError(f'Encrypted Data has invalid format, expected {KEY_FORMAT}, got {parts}')

    enc_type = parts[1]
    enc_data_part = parts[2]

    if parts[0] != 'enc':
        # parts ok but without our header ?
        return enc_data

    # at that stage we know it's our encryption
    if enc_type == 'aes':
        decrypted_data = AESCipher(enc_key).decrypt(enc_data_part, safe=safe)
    elif enc_type == 'aes_hmac':
        decrypted_data = AESCipher(
            enc_key, hmac=True,
            strict_verification=enc_strict_mode).decrypt(enc_data_part, safe=safe)

    else:
        raise ValueError(
            f'Encryption type part is wrong, must be `aes` '
            f'or `aes_hmac`, got `{enc_type}` instead')

    return decrypted_data


def encrypt_data(data, enc_key: bytes):
    enc_key = safe_bytes(enc_key)
    enc_value = AESCipher(enc_key, hmac=True).encrypt(safe_bytes(data))
    return KEY_FORMAT.replace(b'{1}', enc_value)