Source code for nacl.secret

# 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
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# See the License for the specific language governing permissions and
# limitations under the License.

from __future__ import absolute_import, division, print_function

import nacl.bindings
from nacl import encoding
from nacl import exceptions as exc
from nacl.utils import EncryptedMessage, StringFixer, random

[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. :cvar MACBYTES: The size of the authentication MAC tag in bytes. :cvar MESSAGEBYTES_MAX: The maximum size of a message which can be safely encrypted with a single key/nonce pair. """ KEY_SIZE = nacl.bindings.crypto_secretbox_KEYBYTES NONCE_SIZE = nacl.bindings.crypto_secretbox_NONCEBYTES MACBYTES = nacl.bindings.crypto_secretbox_MACBYTES MESSAGEBYTES_MAX = nacl.bindings.crypto_secretbox_MESSAGEBYTES_MAX def __init__(self, key, encoder=encoding.RawEncoder): key = encoder.decode(key) if not isinstance(key, bytes): raise exc.TypeError("SecretBox must be created from 32 bytes") if len(key) != self.KEY_SIZE: raise exc.ValueError( "The key must be exactly %s bytes long" % self.KEY_SIZE, ) self._key = key def __bytes__(self): return self._key
[docs] def encrypt(self, plaintext, nonce=None, encoder=encoding.RawEncoder): """ Encrypts the plaintext message using the given `nonce` (or generates one randomly if omitted) 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 nonce is None: nonce = random(self.NONCE_SIZE) if len(nonce) != self.NONCE_SIZE: raise exc.ValueError( "The nonce must be exactly %s bytes long" % self.NONCE_SIZE, ) ciphertext = nacl.bindings.crypto_secretbox(plaintext, nonce, self._key) 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 `nonce` (explicitly, when passed as a parameter or implicitly, when omitted, as part of the ciphertext) 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 exc.ValueError( "The nonce must be exactly %s bytes long" % self.NONCE_SIZE, ) plaintext = nacl.bindings.crypto_secretbox_open(ciphertext, nonce, self._key) return plaintext