306 lines
12 KiB
Python
306 lines
12 KiB
Python
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# Copyright 2013 Donald Stufft and individual contributors
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from typing import ClassVar, Optional
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import nacl.bindings
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from nacl import encoding
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from nacl import exceptions as exc
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from nacl.utils import EncryptedMessage, StringFixer, random
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class SecretBox(encoding.Encodable, StringFixer):
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"""
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The SecretBox class encrypts and decrypts messages using the given secret
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key.
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The ciphertexts generated by :class:`~nacl.secret.Secretbox` include a 16
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byte authenticator which is checked as part of the decryption. An invalid
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authenticator will cause the decrypt function to raise an exception. The
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authenticator is not a signature. Once you've decrypted the message you've
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demonstrated the ability to create arbitrary valid message, so messages you
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send are repudiable. For non-repudiable messages, sign them after
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encryption.
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Encryption is done using `XSalsa20-Poly1305`_, and there are no practical
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limits on the number or size of messages (up to 2⁶⁴ messages, each up to 2⁶⁴
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bytes).
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.. _XSalsa20-Poly1305: https://doc.libsodium.org/secret-key_cryptography/secretbox#algorithm-details
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:param key: The secret key used to encrypt and decrypt messages
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:param encoder: The encoder class used to decode the given key
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:cvar KEY_SIZE: The size that the key is required to be.
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:cvar NONCE_SIZE: The size that the nonce is required to be.
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:cvar MACBYTES: The size of the authentication MAC tag in bytes.
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:cvar MESSAGEBYTES_MAX: The maximum size of a message which can be
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safely encrypted with a single key/nonce
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pair.
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"""
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KEY_SIZE: ClassVar[int] = nacl.bindings.crypto_secretbox_KEYBYTES
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NONCE_SIZE: ClassVar[int] = nacl.bindings.crypto_secretbox_NONCEBYTES
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MACBYTES: ClassVar[int] = nacl.bindings.crypto_secretbox_MACBYTES
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MESSAGEBYTES_MAX: ClassVar[
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int
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] = nacl.bindings.crypto_secretbox_MESSAGEBYTES_MAX
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def __init__(
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self, key: bytes, encoder: encoding.Encoder = encoding.RawEncoder
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):
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key = encoder.decode(key)
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if not isinstance(key, bytes):
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raise exc.TypeError("SecretBox must be created from 32 bytes")
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if len(key) != self.KEY_SIZE:
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raise exc.ValueError(
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"The key must be exactly %s bytes long" % self.KEY_SIZE,
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)
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self._key = key
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def __bytes__(self) -> bytes:
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return self._key
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def encrypt(
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self,
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plaintext: bytes,
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nonce: Optional[bytes] = None,
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encoder: encoding.Encoder = encoding.RawEncoder,
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) -> EncryptedMessage:
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"""
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Encrypts the plaintext message using the given `nonce` (or generates
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one randomly if omitted) and returns the ciphertext encoded with the
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encoder.
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.. warning:: It is **VITALLY** important that the nonce is a nonce,
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i.e. it is a number used only once for any given key. If you fail
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to do this, you compromise the privacy of the messages encrypted.
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Give your nonces a different prefix, or have one side use an odd
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counter and one an even counter. Just make sure they are different.
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:param plaintext: [:class:`bytes`] The plaintext message to encrypt
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:param nonce: [:class:`bytes`] The nonce to use in the encryption
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:param encoder: The encoder to use to encode the ciphertext
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:rtype: [:class:`nacl.utils.EncryptedMessage`]
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"""
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if nonce is None:
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nonce = random(self.NONCE_SIZE)
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if len(nonce) != self.NONCE_SIZE:
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raise exc.ValueError(
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"The nonce must be exactly %s bytes long" % self.NONCE_SIZE,
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)
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ciphertext = nacl.bindings.crypto_secretbox(
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plaintext, nonce, self._key
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)
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encoded_nonce = encoder.encode(nonce)
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encoded_ciphertext = encoder.encode(ciphertext)
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return EncryptedMessage._from_parts(
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encoded_nonce,
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encoded_ciphertext,
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encoder.encode(nonce + ciphertext),
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)
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def decrypt(
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self,
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ciphertext: bytes,
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nonce: Optional[bytes] = None,
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encoder: encoding.Encoder = encoding.RawEncoder,
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) -> bytes:
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"""
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Decrypts the ciphertext using the `nonce` (explicitly, when passed as a
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parameter or implicitly, when omitted, as part of the ciphertext) and
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returns the plaintext message.
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:param ciphertext: [:class:`bytes`] The encrypted message to decrypt
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:param nonce: [:class:`bytes`] The nonce used when encrypting the
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ciphertext
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:param encoder: The encoder used to decode the ciphertext.
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:rtype: [:class:`bytes`]
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"""
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# Decode our ciphertext
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ciphertext = encoder.decode(ciphertext)
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if nonce is None:
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# If we were given the nonce and ciphertext combined, split them.
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nonce = ciphertext[: self.NONCE_SIZE]
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ciphertext = ciphertext[self.NONCE_SIZE :]
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if len(nonce) != self.NONCE_SIZE:
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raise exc.ValueError(
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"The nonce must be exactly %s bytes long" % self.NONCE_SIZE,
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)
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plaintext = nacl.bindings.crypto_secretbox_open(
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ciphertext, nonce, self._key
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)
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return plaintext
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class Aead(encoding.Encodable, StringFixer):
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"""
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The AEAD class encrypts and decrypts messages using the given secret key.
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Unlike :class:`~nacl.secret.SecretBox`, AEAD supports authenticating
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non-confidential data received alongside the message, such as a length
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or type tag.
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Like :class:`~nacl.secret.Secretbox`, this class provides authenticated
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encryption. An inauthentic message will cause the decrypt function to raise
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an exception.
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Likewise, the authenticator should not be mistaken for a (public-key)
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signature: recipients (with the ability to decrypt messages) are capable of
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creating arbitrary valid message; in particular, this means AEAD messages
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are repudiable. For non-repudiable messages, sign them after encryption.
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The cryptosystem used is `XChacha20-Poly1305`_ as specified for
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`standardization`_. There are `no practical limits`_ to how much can safely
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be encrypted under a given key (up to 2⁶⁴ messages each containing up
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to 2⁶⁴ bytes).
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.. _standardization: https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-xchacha
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.. _XChacha20-Poly1305: https://doc.libsodium.org/secret-key_cryptography/aead#xchacha-20-poly1305
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.. _no practical limits: https://doc.libsodium.org/secret-key_cryptography/aead#limitations
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:param key: The secret key used to encrypt and decrypt messages
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:param encoder: The encoder class used to decode the given key
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:cvar KEY_SIZE: The size that the key is required to be.
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:cvar NONCE_SIZE: The size that the nonce is required to be.
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:cvar MACBYTES: The size of the authentication MAC tag in bytes.
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:cvar MESSAGEBYTES_MAX: The maximum size of a message which can be
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safely encrypted with a single key/nonce
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pair.
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"""
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KEY_SIZE = nacl.bindings.crypto_aead_xchacha20poly1305_ietf_KEYBYTES
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NONCE_SIZE = nacl.bindings.crypto_aead_xchacha20poly1305_ietf_NPUBBYTES
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MACBYTES = nacl.bindings.crypto_aead_xchacha20poly1305_ietf_ABYTES
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MESSAGEBYTES_MAX = (
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nacl.bindings.crypto_aead_xchacha20poly1305_ietf_MESSAGEBYTES_MAX
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)
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def __init__(
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self,
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key: bytes,
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encoder: encoding.Encoder = encoding.RawEncoder,
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):
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key = encoder.decode(key)
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if not isinstance(key, bytes):
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raise exc.TypeError("AEAD must be created from 32 bytes")
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if len(key) != self.KEY_SIZE:
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raise exc.ValueError(
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"The key must be exactly %s bytes long" % self.KEY_SIZE,
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)
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self._key = key
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def __bytes__(self) -> bytes:
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return self._key
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def encrypt(
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self,
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plaintext: bytes,
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aad: bytes = b"",
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nonce: Optional[bytes] = None,
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encoder: encoding.Encoder = encoding.RawEncoder,
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) -> EncryptedMessage:
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"""
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Encrypts the plaintext message using the given `nonce` (or generates
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one randomly if omitted) and returns the ciphertext encoded with the
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encoder.
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.. warning:: It is vitally important for :param nonce: to be unique.
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By default, it is generated randomly; [:class:`Aead`] uses XChacha20
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for extended (192b) nonce size, so the risk of reusing random nonces
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is negligible. It is *strongly recommended* to keep this behaviour,
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as nonce reuse will compromise the privacy of encrypted messages.
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Should implicit nonces be inadequate for your application, the
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second best option is using split counters; e.g. if sending messages
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encrypted under a shared key between 2 users, each user can use the
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number of messages it sent so far, prefixed or suffixed with a 1bit
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user id. Note that the counter must **never** be rolled back (due
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to overflow, on-disk state being rolled back to an earlier backup,
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...)
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:param plaintext: [:class:`bytes`] The plaintext message to encrypt
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:param nonce: [:class:`bytes`] The nonce to use in the encryption
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:param encoder: The encoder to use to encode the ciphertext
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:rtype: [:class:`nacl.utils.EncryptedMessage`]
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"""
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if nonce is None:
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nonce = random(self.NONCE_SIZE)
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if len(nonce) != self.NONCE_SIZE:
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raise exc.ValueError(
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"The nonce must be exactly %s bytes long" % self.NONCE_SIZE,
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)
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ciphertext = nacl.bindings.crypto_aead_xchacha20poly1305_ietf_encrypt(
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plaintext, aad, nonce, self._key
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)
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encoded_nonce = encoder.encode(nonce)
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encoded_ciphertext = encoder.encode(ciphertext)
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return EncryptedMessage._from_parts(
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encoded_nonce,
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encoded_ciphertext,
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encoder.encode(nonce + ciphertext),
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)
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def decrypt(
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self,
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ciphertext: bytes,
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aad: bytes = b"",
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nonce: Optional[bytes] = None,
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encoder: encoding.Encoder = encoding.RawEncoder,
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) -> bytes:
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"""
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Decrypts the ciphertext using the `nonce` (explicitly, when passed as a
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parameter or implicitly, when omitted, as part of the ciphertext) and
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returns the plaintext message.
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:param ciphertext: [:class:`bytes`] The encrypted message to decrypt
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:param nonce: [:class:`bytes`] The nonce used when encrypting the
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ciphertext
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:param encoder: The encoder used to decode the ciphertext.
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:rtype: [:class:`bytes`]
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"""
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# Decode our ciphertext
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ciphertext = encoder.decode(ciphertext)
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if nonce is None:
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# If we were given the nonce and ciphertext combined, split them.
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nonce = ciphertext[: self.NONCE_SIZE]
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ciphertext = ciphertext[self.NONCE_SIZE :]
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if len(nonce) != self.NONCE_SIZE:
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raise exc.ValueError(
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"The nonce must be exactly %s bytes long" % self.NONCE_SIZE,
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)
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plaintext = nacl.bindings.crypto_aead_xchacha20poly1305_ietf_decrypt(
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ciphertext, aad, nonce, self._key
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)
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return plaintext
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