PappyProxy/pappyproxy/crypto.py

#!/usr/bin/env python

import crochet
import getpass
import glob
import os
import pappyproxy
import scrypt
import shutil
import twisted

from . import compress
from .util import PappyException
from base64 import b64encode, b64decode
from cryptography.fernet import Fernet, InvalidToken
from twisted.internet import reactor, defer


class Crypto(object):
    def __init__(self, sessconfig):
        self.config = sessconfig
        self.archive = sessconfig.archive
        self.compressor = compress.Compress(sessconfig)
        self.key = None
        self.password = None
        self.salt = None

    def encrypt_project(self):
        """
        Compress and encrypt the project files,
        deleting clear-text files afterwards
        """

        # Leave the crypto working directory
        if self.config.crypt_dir in os.getcwd():
            os.chdir('../')

        self.compressor.compress_project()

        # Get the password and salt, then derive the key
        self.crypto_ramp_up()

        # Create project and crypto archive
        archive_file = open(self.archive, 'rb')
        archive_crypt = open(self.config.crypt_file, 'wb')

        try:
            # Encrypt the archive read as a bytestring
            fern = Fernet(self.key)
            crypt_token = fern.encrypt(archive_file.read())
            archive_crypt.write(crypt_token)
        except InvalidToken as e:
            raise PappyException("Error encrypting project: ", e)
            return False

        archive_file.close()
        archive_crypt.close()

        # Store the salt for the next decryption
        self.create_salt_file()

        # Delete clear-text files
        self.delete_clear_files()
        return True

    def decrypt_project(self):
        """
        Decrypt and decompress the project files
        """

        # If project hasn't been encrypted before,
        # setup crypt working directory
        if not os.path.isfile(self.config.crypt_file):
            os.mkdir(self.config.crypt_dir)

            project_files = self.config.get_project_files()
            for pf in project_files:
                shutil.copy2(pf, self.config.crypt_dir)
            os.chdir(self.config.crypt_dir)
            return True

        # Otherwise, decrypt and decompress the project
        else:
            cf = self.config.crypt_file
            sl = self.config.salt_len
            crl = os.path.getsize(cf) - sl

            archive_crypt = open(cf, 'rb').read(crl)
            archive_file = open(self.config.archive, 'wb')

            retries = 3
            while True:
                try:
                    self.crypto_ramp_up()
                    fern = Fernet(self.key)
                    archive = fern.decrypt(archive_crypt)
                    break
                except InvalidToken as e:
                    print "Invalid decryption: ", e
                    retries -= 1
                    # Quit pappy if user doesn't retry
                    # or if all retries exhuasted
                    if not self.confirm_password_retry() or retries <= 0:
                        return False
                    else:
                        self.password = None
                        self.key = None
                        pass

            archive_file.write(archive)
            archive_file.close()

            self.compressor.decompress_project()

            os.chdir(self.config.crypt_dir)
            return True

    def confirm_password_retry(self):
        answer = raw_input("Re-enter your password? (y/n): ").strip()
        if answer[0] == "y" or answer[0] == "Y":
            return True
        else:
            return False

    def crypto_ramp_up(self):
        if not self.password:
            self.get_password()
        if not self.salt:
            self.set_salt()
        self.derive_key()

    def get_password(self):
        """
        Retrieve password from the user. Raise an exception if the
        password is not capable of utf-8 encoding.
        """
        encoded_passwd = ""
        try:
            passwd = getpass.getpass("Enter a password: ").strip()
            self.password = passwd.encode("utf-8")
        except:
            raise PappyException("Invalid password, try again")

    def set_salt(self):
        if self.config.crypt_dir in os.getcwd():
            os.chdir('../')
            self.set_salt_from_file()
            os.chdir(self.config.crypt_dir)
        elif os.path.isfile(self.config.crypt_file):
            self.set_salt_from_file()
        else:
            self.salt = os.urandom(16)

    def set_salt_from_file(self):
        try:
            # Seek to `salt_len` bytes before the EOF
            # then read `salt_len` bytes to retrieve the salt

            # WARNING: must open `crypt_file` in `rb` mode
            # or `salt_file.seek()` will result in undefined
            # behavior.
            salt_file = open(self.config.crypt_file, 'rb')
            sl = self.config.salt_len
            # Negate the salt length to seek to the 
            # correct position in the buffer
            salt_file.seek(-sl, 2)
            self.salt = salt_file.read(sl)
            salt_file.close()
        except:
            cf = self.config.crypt_file
            raise PappyException("Unable to read %s" % cf)

    def create_salt_file(self):
        salt_file = open(self.config.crypt_file, 'a')
        salt_file.write(self.salt)
        salt_file.close()

    def derive_key(self):
        """
        Derive a key sufficient for use as a cryptographic key
        used to encrypt the project (currently: cryptography.Fernet).

        cryptography.Fernet utilizes AES-CBC-128, requiring a 32-byte key.
        Parameter notes from the py-scrypt source-code:
        https://bitbucket.org/mhallin/py-scrypt/

        Compute scrypt(password, salt, N, r, p, buflen).

        The parameters r, p, and buflen must satisfy r * p < 2^30 and
        buflen <= (2^32 - 1) * 32. The parameter N must be a power of 2
        greater than 1. N, r and p must all be positive.

        Notes for Python 2:
          - `password` and `salt` must be str instances
          - The result will be a str instance

        Notes for Python 3:
          - `password` and `salt` can be both str and bytes. If they are str
            instances, they wil be encoded with utf-8.
          - The result will be a bytes instance

        Exceptions raised:
          - TypeError on invalid input
          - scrypt.error if scrypt failed
        """

        try:
            if not self.key:
                shash = scrypt.hash(self.password, self.salt, buflen=32)
                self.key = b64encode(shash)
        except TypeError as e:
            raise PappyException("Scrypt failed with type error: ", e)
        except scrypt.error, e:
            raise PappyException("Scrypt failed with internal error: ", e)

    def delete_clear_files(self):
        """
        Deletes all clear-text files left in the project directory.
        """
        shutil.rmtree(self.config.crypt_dir)
        os.remove(self.config.archive)

    def delete_crypt_files(self):
        """
        Deletes all encrypted-text files in the project directory.
        Forces generation of new salt after opening and closing the project.
        Adds security in the case of a one-time compromise of the system.
        """
        os.remove(self.config.crypt_file)