Mini Shell

# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.

from __future__ import absolute_import, division, print_function

import abc

import six

from cryptography import utils
from cryptography.exceptions import (
    AlreadyFinalized,
    AlreadyUpdated,
    NotYetFinalized,
    UnsupportedAlgorithm,
    _Reasons,
)
from cryptography.hazmat.backends import _get_backend
from cryptography.hazmat.backends.interfaces import CipherBackend
from cryptography.hazmat.primitives.ciphers import modes


@six.add_metaclass(abc.ABCMeta)
class CipherAlgorithm(object):
    @abc.abstractproperty
    def name(self):
        """
        A string naming this mode (e.g. "AES", "Camellia").
        """

    @abc.abstractproperty
    def key_size(self):
        """
        The size of the key being used as an integer in bits (e.g. 128, 256).
        """


@six.add_metaclass(abc.ABCMeta)
class BlockCipherAlgorithm(object):
    @abc.abstractproperty
    def block_size(self):
        """
        The size of a block as an integer in bits (e.g. 64, 128).
        """


@six.add_metaclass(abc.ABCMeta)
class CipherContext(object):
    @abc.abstractmethod
    def update(self, data):
        """
        Processes the provided bytes through the cipher and returns the results
        as bytes.
        """

    @abc.abstractmethod
    def update_into(self, data, buf):
        """
        Processes the provided bytes and writes the resulting data into the
        provided buffer. Returns the number of bytes written.
        """

    @abc.abstractmethod
    def finalize(self):
        """
        Returns the results of processing the final block as bytes.
        """


@six.add_metaclass(abc.ABCMeta)
class AEADCipherContext(object):
    @abc.abstractmethod
    def authenticate_additional_data(self, data):
        """
        Authenticates the provided bytes.
        """


@six.add_metaclass(abc.ABCMeta)
class AEADDecryptionContext(object):
    @abc.abstractmethod
    def finalize_with_tag(self, tag):
        """
        Returns the results of processing the final block as bytes and allows
        delayed passing of the authentication tag.
        """


@six.add_metaclass(abc.ABCMeta)
class AEADEncryptionContext(object):
    @abc.abstractproperty
    def tag(self):
        """
        Returns tag bytes. This is only available after encryption is
        finalized.
        """


class Cipher(object):
    def __init__(self, algorithm, mode, backend=None):
        backend = _get_backend(backend)
        if not isinstance(backend, CipherBackend):
            raise UnsupportedAlgorithm(
                "Backend object does not implement CipherBackend.",
                _Reasons.BACKEND_MISSING_INTERFACE,
            )

        if not isinstance(algorithm, CipherAlgorithm):
            raise TypeError("Expected interface of CipherAlgorithm.")

        if mode is not None:
            mode.validate_for_algorithm(algorithm)

        self.algorithm = algorithm
        self.mode = mode
        self._backend = backend

    def encryptor(self):
        if isinstance(self.mode, modes.ModeWithAuthenticationTag):
            if self.mode.tag is not None:
                raise ValueError(
                    "Authentication tag must be None when encrypting."
                )
        ctx = self._backend.create_symmetric_encryption_ctx(
            self.algorithm, self.mode
        )
        return self._wrap_ctx(ctx, encrypt=True)

    def decryptor(self):
        ctx = self._backend.create_symmetric_decryption_ctx(
            self.algorithm, self.mode
        )
        return self._wrap_ctx(ctx, encrypt=False)

    def _wrap_ctx(self, ctx, encrypt):
        if isinstance(self.mode, modes.ModeWithAuthenticationTag):
            if encrypt:
                return _AEADEncryptionContext(ctx)
            else:
                return _AEADCipherContext(ctx)
        else:
            return _CipherContext(ctx)


@utils.register_interface(CipherContext)
class _CipherContext(object):
    def __init__(self, ctx):
        self._ctx = ctx

    def update(self, data):
        if self._ctx is None:
            raise AlreadyFinalized("Context was already finalized.")
        return self._ctx.update(data)

    def update_into(self, data, buf):
        if self._ctx is None:
            raise AlreadyFinalized("Context was already finalized.")
        return self._ctx.update_into(data, buf)

    def finalize(self):
        if self._ctx is None:
            raise AlreadyFinalized("Context was already finalized.")
        data = self._ctx.finalize()
        self._ctx = None
        return data


@utils.register_interface(AEADCipherContext)
@utils.register_interface(CipherContext)
@utils.register_interface(AEADDecryptionContext)
class _AEADCipherContext(object):
    def __init__(self, ctx):
        self._ctx = ctx
        self._bytes_processed = 0
        self._aad_bytes_processed = 0
        self._tag = None
        self._updated = False

    def _check_limit(self, data_size):
        if self._ctx is None:
            raise AlreadyFinalized("Context was already finalized.")
        self._updated = True
        self._bytes_processed += data_size
        if self._bytes_processed > self._ctx._mode._MAX_ENCRYPTED_BYTES:
            raise ValueError(
                "{} has a maximum encrypted byte limit of {}".format(
                    self._ctx._mode.name, self._ctx._mode._MAX_ENCRYPTED_BYTES
                )
            )

    def update(self, data):
        self._check_limit(len(data))
        return self._ctx.update(data)

    def update_into(self, data, buf):
        self._check_limit(len(data))
        return self._ctx.update_into(data, buf)

    def finalize(self):
        if self._ctx is None:
            raise AlreadyFinalized("Context was already finalized.")
        data = self._ctx.finalize()
        self._tag = self._ctx.tag
        self._ctx = None
        return data

    def finalize_with_tag(self, tag):
        if self._ctx is None:
            raise AlreadyFinalized("Context was already finalized.")
        data = self._ctx.finalize_with_tag(tag)
        self._tag = self._ctx.tag
        self._ctx = None
        return data

    def authenticate_additional_data(self, data):
        if self._ctx is None:
            raise AlreadyFinalized("Context was already finalized.")
        if self._updated:
            raise AlreadyUpdated("Update has been called on this context.")

        self._aad_bytes_processed += len(data)
        if self._aad_bytes_processed > self._ctx._mode._MAX_AAD_BYTES:
            raise ValueError(
                "{} has a maximum AAD byte limit of {}".format(
                    self._ctx._mode.name, self._ctx._mode._MAX_AAD_BYTES
                )
            )

        self._ctx.authenticate_additional_data(data)


@utils.register_interface(AEADEncryptionContext)
class _AEADEncryptionContext(_AEADCipherContext):
    @property
    def tag(self):
        if self._ctx is not None:
            raise NotYetFinalized(
                "You must finalize encryption before " "getting the tag."
            )
        return self._tag