# Copyright 2013 Donald Stufft and individual contributors
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from __future__ import absolute_import
from __future__ import division
import nacl.c
from . import encoding
from .utils import EncryptedMessage, StringFixer
[docs]class SecretBox(encoding.Encodable, StringFixer, object):
"""
The SecretBox class encrypts and decrypts messages using the given secret
key.
The ciphertexts generated by :class:`~nacl.secret.Secretbox` include a 16
byte authenticator which is checked as part of the decryption. An invalid
authenticator will cause the decrypt function to raise an exception. The
authenticator is not a signature. Once you've decrypted the message you've
demonstrated the ability to create arbitrary valid message, so messages you
send are repudiable. For non-repudiable messages, sign them after
encryption.
:param key: The secret key used to encrypt and decrypt messages
:param encoder: The encoder class used to decode the given key
:cvar KEY_SIZE: The size that the key is required to be.
:cvar NONCE_SIZE: The size that the nonce is required to be.
"""
KEY_SIZE = nacl.c.crypto_secretbox_KEYBYTES
NONCE_SIZE = nacl.c.crypto_secretbox_NONCEBYTES
def __init__(self, key, encoder=encoding.RawEncoder):
key = encoder.decode(key)
if len(key) != self.KEY_SIZE:
raise ValueError(
"The key must be exactly %s bytes long" %
nacl.lib.crypto_secretbox_KEYBYTES,
)
self._key = key
def __bytes__(self):
return self._key
[docs] def encrypt(self, plaintext, nonce, encoder=encoding.RawEncoder):
"""
Encrypts the plaintext message using the given nonce and returns the
ciphertext encoded with the encoder.
.. warning:: It is **VITALLY** important that the nonce is a nonce,
i.e. it is a number used only once for any given key. If you fail
to do this, you compromise the privacy of the messages encrypted.
Give your nonces a different prefix, or have one side use an odd
counter and one an even counter. Just make sure they are different.
:param plaintext: [:class:`bytes`] The plaintext message to encrypt
:param nonce: [:class:`bytes`] The nonce to use in the encryption
:param encoder: The encoder to use to encode the ciphertext
:rtype: [:class:`nacl.utils.EncryptedMessage`]
"""
if len(nonce) != self.NONCE_SIZE:
raise ValueError(
"The nonce must be exactly %s bytes long" % self.NONCE_SIZE,
)
ciphertext = nacl.c.crypto_secretbox(self._key, plaintext, nonce)
encoded_nonce = encoder.encode(nonce)
encoded_ciphertext = encoder.encode(ciphertext)
return EncryptedMessage._from_parts(
encoded_nonce,
encoded_ciphertext,
encoder.encode(nonce + ciphertext),
)
[docs] def decrypt(self, ciphertext, nonce=None, encoder=encoding.RawEncoder):
"""
Decrypts the ciphertext using the given nonce and returns the plaintext
message.
:param ciphertext: [:class:`bytes`] The encrypted message to decrypt
:param nonce: [:class:`bytes`] The nonce used when encrypting the
ciphertext
:param encoder: The encoder used to decode the ciphertext.
:rtype: [:class:`bytes`]
"""
# Decode our ciphertext
ciphertext = encoder.decode(ciphertext)
if nonce is None:
# If we were given the nonce and ciphertext combined, split them.
nonce = ciphertext[:self.NONCE_SIZE]
ciphertext = ciphertext[self.NONCE_SIZE:]
if len(nonce) != self.NONCE_SIZE:
raise ValueError(
"The nonce must be exactly %s bytes long" % self.NONCE_SIZE,
)
plaintext = nacl.c.crypto_secretbox_open(self._key, ciphertext, nonce)
return plaintext