borg/darc/keychain.py

from getpass import getpass
import hashlib
import os
import msgpack
import zlib

from pbkdf2 import pbkdf2
from Crypto.Cipher import AES
from Crypto.Hash import SHA256, HMAC
from Crypto.PublicKey import RSA
from Crypto.Util import Counter
from Crypto.Util.number import bytes_to_long

from .helpers import IntegrityError
from .oaep import OAEP


class Keychain(object):
    FILE_ID = 'DARC KEYCHAIN'

    CREATE = '\1'
    READ = '\2'

    def __init__(self, path=None):
        self._key_cache = {}
        self.read_key = os.urandom(32)
        self.create_key = os.urandom(32)
        self.aes_id = self.rsa_read = self.rsa_create = None
        self.path = path
        if path:
            self.open(path)

    def open(self, path):
        print 'Opening keychain "%s"' % path
        with open(path, 'rb') as fd:
            if fd.read(len(self.FILE_ID)) != self.FILE_ID:
                raise ValueError('Not a keychain')
            cdata = fd.read()
        self.password = ''
        data = self._decrypt(cdata, '')
        while not data:
            self.password = getpass('Keychain password: ')
            if not self.password:
                raise Exception('Keychain decryption failed')
            data = self.decrypt(cdata, self.password)
            if not data:
                print 'Incorrect password'
        chain = msgpack.unpackb(data)
        assert chain['version'] == 1
        self.aes_id = chain['aes_id']
        self.rsa_read = RSA.importKey(chain['rsa_read'])
        self.rsa_create = RSA.importKey(chain['rsa_create'])
        self.read_encrypted = OAEP(256, hash=SHA256).encode(self.read_key, os.urandom(32))
        self.read_encrypted = self.rsa_read.encrypt(self.read_encrypted, '')[0]
        self.create_encrypted = OAEP(256, hash=SHA256).encode(self.create_key, os.urandom(32))
        self.create_encrypted = self.rsa_create.encrypt(self.create_encrypted, '')[0]

    def encrypt(self, data, password):
        salt = os.urandom(32)
        iterations = 2000
        key = pbkdf2(password, salt, 32, iterations, hashlib.sha256)
        hash = HMAC.new(key, data, SHA256).digest()
        cdata = AES.new(key, AES.MODE_CTR, counter=Counter.new(128)).encrypt(data)
        d = {
            'version': 1,
            'salt': salt,
            'iterations': iterations,
            'algorithm': 'SHA256',
            'hash': hash,
            'data': cdata,
        }
        return msgpack.packb(d)

    def _decrypt(self, data, password):
        d = msgpack.unpackb(data)
        assert d['version'] == 1
        assert d['algorithm'] == 'SHA256'
        key = pbkdf2(password, d['salt'], 32, d['iterations'], hashlib.sha256)
        data = AES.new(key, AES.MODE_CTR, counter=Counter.new(128)).decrypt(d['data'])
        if HMAC.new(key, data, SHA256).digest() != d['hash']:
            return None
        return data

    def save(self, path, password):
        chain = {
            'version': 1,
            'aes_id': self.aes_id,
            'rsa_read': self.rsa_read.exportKey('PEM'),
            'rsa_create': self.rsa_create.exportKey('PEM'),
        }
        data = self.encrypt(msgpack.packb(chain), password)
        with open(path, 'wb') as fd:
            fd.write(self.FILE_ID)
            fd.write(data)
            print 'Key chain "%s" saved' % path

    def restrict(self, path):
        if os.path.exists(path):
            print '%s already exists' % path
            return 1
        self.rsa_read = self.rsa_read.publickey()
        self.save(path, self.password)
        return 0

    def chpass(self):
        password, password2 = 1, 2
        while password != password2:
            password = getpass('New password: ')
            password2 = getpass('New password again: ')
            if password != password2:
                print 'Passwords do not match'
        self.save(self.path, password)
        return 0

    @staticmethod
    def generate(path):
        if os.path.exists(path):
            print '%s already exists' % path
            return 1
        password, password2 = 1, 2
        while password != password2:
            password = getpass('Keychain password: ')
            password2 = getpass('Keychain password again: ')
            if password != password2:
                print 'Passwords do not match'
        chain = Keychain()
        print 'Generating keychain'
        chain.aes_id = os.urandom(32)
        chain.rsa_read = RSA.generate(2048)
        chain.rsa_create = RSA.generate(2048)
        chain.save(path, password)
        return 0

    def id_hash(self, data):
        return HMAC.new(self.aes_id, data, SHA256).digest()

    def encrypt_read(self, data):
        data = zlib.compress(data)
        hash = self.id_hash(data)
        counter = Counter.new(128, initial_value=bytes_to_long(hash[:16]), allow_wraparound=True)
        data = AES.new(self.read_key, AES.MODE_CTR, '', counter=counter).encrypt(data)
        return ''.join((self.READ, self.read_encrypted, hash, data)), hash

    def encrypt_create(self, data):
        data = zlib.compress(data)
        hash = self.id_hash(data)
        counter = Counter.new(128, initial_value=bytes_to_long(hash[:16]), allow_wraparound=True)
        data = AES.new(self.create_key, AES.MODE_CTR, '', counter=counter).encrypt(data)
        return ''.join((self.CREATE, self.create_encrypted, hash, data)), hash

    def decrypt_key(self, data, rsa_key):
        try:
            return self._key_cache[data]
        except KeyError:
            self._key_cache[data] = OAEP(256, hash=SHA256).decode(rsa_key.decrypt(data))
            return self._key_cache[data]

    def decrypt(self, data):
        type = data[0]
        if type == self.READ:
            key = self.decrypt_key(data[1:257], self.rsa_read)
            hash = data[257:289]
            counter = Counter.new(128, initial_value=bytes_to_long(hash[:16]), allow_wraparound=True)
            data = AES.new(key, AES.MODE_CTR, counter=counter).decrypt(data[289:])
            if self.id_hash(data) != hash:
                raise IntegrityError('decryption failed')
            return zlib.decompress(data), hash
        elif type == self.CREATE:
            key = self.decrypt_key(data[1:257], self.rsa_create)
            hash = data[257:289]
            counter = Counter.new(128, initial_value=bytes_to_long(hash[:16]), allow_wraparound=True)
            data = AES.new(key, AES.MODE_CTR, '', counter=counter).decrypt(data[289:])
            if self.id_hash(data) != hash:
                raise IntegrityError('decryption failed')
            return zlib.decompress(data), hash
        else:
            raise Exception('Unknown pack type %d found' % ord(type))