# 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 typing import ClassVar, Optional
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):
"""
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.
Encryption is done using `XSalsa20-Poly1305`_, and there are no practical
limits on the number or size of messages (up to 2⁶⁴ messages, each up to 2⁶⁴
bytes).
.. _XSalsa20-Poly1305: https://doc.libsodium.org/secret-key_cryptography/secretbox#algorithm-details
: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: ClassVar[int] = nacl.bindings.crypto_secretbox_KEYBYTES
NONCE_SIZE: ClassVar[int] = nacl.bindings.crypto_secretbox_NONCEBYTES
MACBYTES: ClassVar[int] = nacl.bindings.crypto_secretbox_MACBYTES
MESSAGEBYTES_MAX: ClassVar[int] = (
nacl.bindings.crypto_secretbox_MESSAGEBYTES_MAX
)
def __init__(
self, key: bytes, encoder: encoding.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) -> bytes:
return self._key
[docs] def encrypt(
self,
plaintext: bytes,
nonce: Optional[bytes] = None,
encoder: encoding.Encoder = encoding.RawEncoder,
) -> EncryptedMessage:
"""
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: bytes,
nonce: Optional[bytes] = None,
encoder: encoding.Encoder = encoding.RawEncoder,
) -> bytes:
"""
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
class Aead(encoding.Encodable, StringFixer):
"""
The AEAD class encrypts and decrypts messages using the given secret key.
Unlike :class:`~nacl.secret.SecretBox`, AEAD supports authenticating
non-confidential data received alongside the message, such as a length
or type tag.
Like :class:`~nacl.secret.Secretbox`, this class provides authenticated
encryption. An inauthentic message will cause the decrypt function to raise
an exception.
Likewise, the authenticator should not be mistaken for a (public-key)
signature: recipients (with the ability to decrypt messages) are capable of
creating arbitrary valid message; in particular, this means AEAD messages
are repudiable. For non-repudiable messages, sign them after encryption.
The cryptosystem used is `XChacha20-Poly1305`_ as specified for
`standardization`_. There are `no practical limits`_ to how much can safely
be encrypted under a given key (up to 2⁶⁴ messages each containing up
to 2⁶⁴ bytes).
.. _standardization: https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-xchacha
.. _XChacha20-Poly1305: https://doc.libsodium.org/secret-key_cryptography/aead#xchacha-20-poly1305
.. _no practical limits: https://doc.libsodium.org/secret-key_cryptography/aead#limitations
: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_aead_xchacha20poly1305_ietf_KEYBYTES
NONCE_SIZE = nacl.bindings.crypto_aead_xchacha20poly1305_ietf_NPUBBYTES
MACBYTES = nacl.bindings.crypto_aead_xchacha20poly1305_ietf_ABYTES
MESSAGEBYTES_MAX = (
nacl.bindings.crypto_aead_xchacha20poly1305_ietf_MESSAGEBYTES_MAX
)
def __init__(
self,
key: bytes,
encoder: encoding.Encoder = encoding.RawEncoder,
):
key = encoder.decode(key)
if not isinstance(key, bytes):
raise exc.TypeError("AEAD 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) -> bytes:
return self._key
def encrypt(
self,
plaintext: bytes,
aad: bytes = b"",
nonce: Optional[bytes] = None,
encoder: encoding.Encoder = encoding.RawEncoder,
) -> EncryptedMessage:
"""
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 for :param nonce: to be unique.
By default, it is generated randomly; [:class:`Aead`] uses XChacha20
for extended (192b) nonce size, so the risk of reusing random nonces
is negligible. It is *strongly recommended* to keep this behaviour,
as nonce reuse will compromise the privacy of encrypted messages.
Should implicit nonces be inadequate for your application, the
second best option is using split counters; e.g. if sending messages
encrypted under a shared key between 2 users, each user can use the
number of messages it sent so far, prefixed or suffixed with a 1bit
user id. Note that the counter must **never** be rolled back (due
to overflow, on-disk state being rolled back to an earlier backup,
...)
: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_aead_xchacha20poly1305_ietf_encrypt(
plaintext, aad, 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),
)
def decrypt(
self,
ciphertext: bytes,
aad: bytes = b"",
nonce: Optional[bytes] = None,
encoder: encoding.Encoder = encoding.RawEncoder,
) -> bytes:
"""
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_aead_xchacha20poly1305_ietf_decrypt(
ciphertext, aad, nonce, self._key
)
return plaintext