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.. hazmat:: Authenticated encryption ======================== .. module:: cryptography.hazmat.primitives.ciphers.aead Authenticated encryption with associated data (AEAD) are encryption schemes which provide both confidentiality and integrity for their ciphertext. They also support providing integrity for associated data which is not encrypted. .. class:: ChaCha20Poly1305(key) .. versionadded:: 2.0 The ChaCha20Poly1305 construction is defined in :rfc:`7539` section 2.8. It is a stream cipher combined with a MAC that offers strong integrity guarantees. :param key: A 32-byte key. This **must** be kept secret. :type key: :term:`bytes-like` :raises cryptography.exceptions.UnsupportedAlgorithm: If the version of OpenSSL does not support ChaCha20Poly1305. .. doctest:: >>> import os >>> from cryptography.hazmat.primitives.ciphers.aead import ChaCha20Poly1305 >>> data = b"a secret message" >>> aad = b"authenticated but unencrypted data" >>> key = ChaCha20Poly1305.generate_key() >>> chacha = ChaCha20Poly1305(key) >>> nonce = os.urandom(12) >>> ct = chacha.encrypt(nonce, data, aad) >>> chacha.decrypt(nonce, ct, aad) b'a secret message' .. classmethod:: generate_key() Securely generates a random ChaCha20Poly1305 key. :returns bytes: A 32 byte key. .. method:: encrypt(nonce, data, associated_data) .. warning:: Reuse of a ``nonce`` with a given ``key`` compromises the security of any message with that ``nonce`` and ``key`` pair. Encrypts the ``data`` provided and authenticates the ``associated_data``. The output of this can be passed directly to the ``decrypt`` method. :param nonce: A 12 byte value. **NEVER REUSE A NONCE** with a key. :type nonce: :term:`bytes-like` :param data: The data to encrypt. :type data: :term:`bytes-like` :param associated_data: Additional data that should be authenticated with the key, but does not need to be encrypted. Can be ``None``. :type associated_data: :term:`bytes-like` :returns bytes: The ciphertext bytes with the 16 byte tag appended. :raises OverflowError: If ``data`` or ``associated_data`` is larger than 2\ :sup:`31` - 1 bytes. .. method:: decrypt(nonce, data, associated_data) Decrypts the ``data`` and authenticates the ``associated_data``. If you called encrypt with ``associated_data`` you must pass the same ``associated_data`` in decrypt or the integrity check will fail. :param nonce: A 12 byte value. **NEVER REUSE A NONCE** with a key. :type nonce: :term:`bytes-like` :param data: The data to decrypt (with tag appended). :type data: :term:`bytes-like` :param associated_data: Additional data to authenticate. Can be ``None`` if none was passed during encryption. :type associated_data: :term:`bytes-like` :returns bytes: The original plaintext. :raises cryptography.exceptions.InvalidTag: If the authentication tag doesn't validate this exception will be raised. This will occur when the ciphertext has been changed, but will also occur when the key, nonce, or associated data are wrong. .. class:: AESGCM(key) .. versionadded:: 2.0 The AES-GCM construction is composed of the :class:`~cryptography.hazmat.primitives.ciphers.algorithms.AES` block cipher utilizing Galois Counter Mode (GCM). :param key: A 128, 192, or 256-bit key. This **must** be kept secret. :type key: :term:`bytes-like` .. doctest:: >>> import os >>> from cryptography.hazmat.primitives.ciphers.aead import AESGCM >>> data = b"a secret message" >>> aad = b"authenticated but unencrypted data" >>> key = AESGCM.generate_key(bit_length=128) >>> aesgcm = AESGCM(key) >>> nonce = os.urandom(12) >>> ct = aesgcm.encrypt(nonce, data, aad) >>> aesgcm.decrypt(nonce, ct, aad) b'a secret message' .. classmethod:: generate_key(bit_length) Securely generates a random AES-GCM key. :param bit_length: The bit length of the key to generate. Must be 128, 192, or 256. :returns bytes: The generated key. .. method:: encrypt(nonce, data, associated_data) .. warning:: Reuse of a ``nonce`` with a given ``key`` compromises the security of any message with that ``nonce`` and ``key`` pair. Encrypts and authenticates the ``data`` provided as well as authenticating the ``associated_data``. The output of this can be passed directly to the ``decrypt`` method. :param nonce: NIST `recommends a 96-bit IV length`_ for best performance but it can be up to 2\ :sup:`64` - 1 :term:`bits`. **NEVER REUSE A NONCE** with a key. :type nonce: :term:`bytes-like` :param data: The data to encrypt. :type data: :term:`bytes-like` :param associated_data: Additional data that should be authenticated with the key, but is not encrypted. Can be ``None``. :type associated_data: :term:`bytes-like` :returns bytes: The ciphertext bytes with the 16 byte tag appended. :raises OverflowError: If ``data`` or ``associated_data`` is larger than 2\ :sup:`31` - 1 bytes. .. method:: decrypt(nonce, data, associated_data) Decrypts the ``data`` and authenticates the ``associated_data``. If you called encrypt with ``associated_data`` you must pass the same ``associated_data`` in decrypt or the integrity check will fail. :param nonce: NIST `recommends a 96-bit IV length`_ for best performance but it can be up to 2\ :sup:`64` - 1 :term:`bits`. **NEVER REUSE A NONCE** with a key. :type nonce: :term:`bytes-like` :param data: The data to decrypt (with tag appended). :type data: :term:`bytes-like` :param associated_data: Additional data to authenticate. Can be ``None`` if none was passed during encryption. :type associated_data: :term:`bytes-like` :returns bytes: The original plaintext. :raises cryptography.exceptions.InvalidTag: If the authentication tag doesn't validate this exception will be raised. This will occur when the ciphertext has been changed, but will also occur when the key, nonce, or associated data are wrong. .. class:: AESGCMSIV(key) .. versionadded:: 42.0.0 The AES-GCM-SIV construction is defined in :rfc:`8452` and is composed of the :class:`~cryptography.hazmat.primitives.ciphers.algorithms.AES` block cipher utilizing Galois Counter Mode (GCM) and a synthetic initialization vector (SIV). :param key: A 128, 192, or 256-bit key. This **must** be kept secret. :type key: :term:`bytes-like` :raises cryptography.exceptions.UnsupportedAlgorithm: If the version of OpenSSL does not support AES-GCM-SIV. .. doctest:: >>> import os >>> from cryptography.hazmat.primitives.ciphers.aead import AESGCMSIV >>> data = b"a secret message" >>> aad = b"authenticated but unencrypted data" >>> key = AESGCMSIV.generate_key(bit_length=128) >>> aesgcmsiv = AESGCMSIV(key) >>> nonce = os.urandom(12) >>> ct = aesgcmsiv.encrypt(nonce, data, aad) >>> aesgcmsiv.decrypt(nonce, ct, aad) b'a secret message' .. classmethod:: generate_key(bit_length) Securely generates a random AES-GCM-SIV key. :param bit_length: The bit length of the key to generate. Must be 128, 192, or 256. :returns bytes: The generated key. .. method:: encrypt(nonce, data, associated_data) Encrypts and authenticates the ``data`` provided as well as authenticating the ``associated_data``. The output of this can be passed directly to the ``decrypt`` method. :param nonce: A 12-byte value. :type nonce: :term:`bytes-like` :param data: The data to encrypt. :type data: :term:`bytes-like` :param associated_data: Additional data that should be authenticated with the key, but is not encrypted. Can be ``None``. :type associated_data: :term:`bytes-like` :returns bytes: The ciphertext bytes with the 16 byte tag appended. :raises OverflowError: If ``data`` or ``associated_data`` is larger than 2\ :sup:`32` - 1 bytes. .. method:: decrypt(nonce, data, associated_data) Decrypts the ``data`` and authenticates the ``associated_data``. If you called encrypt with ``associated_data`` you must pass the same ``associated_data`` in decrypt or the integrity check will fail. :param nonce: A 12-byte value. :type nonce: :term:`bytes-like` :param data: The data to decrypt (with tag appended). :type data: :term:`bytes-like` :param associated_data: Additional data to authenticate. Can be ``None`` if none was passed during encryption. :type associated_data: :term:`bytes-like` :returns bytes: The original plaintext. :raises cryptography.exceptions.InvalidTag: If the authentication tag doesn't validate this exception will be raised. This will occur when the ciphertext has been changed, but will also occur when the key, nonce, or associated data are wrong. .. class:: AESOCB3(key) .. versionadded:: 36.0.0 The OCB3 construction is defined in :rfc:`7253`. It is an AEAD mode that offers strong integrity guarantees and good performance. :param key: A 128, 192, or 256-bit key. This **must** be kept secret. :type key: :term:`bytes-like` :raises cryptography.exceptions.UnsupportedAlgorithm: If the version of OpenSSL does not support AES-OCB3. .. doctest:: >>> import os >>> from cryptography.hazmat.primitives.ciphers.aead import AESOCB3 >>> data = b"a secret message" >>> aad = b"authenticated but unencrypted data" >>> key = AESOCB3.generate_key(bit_length=128) >>> aesocb = AESOCB3(key) >>> nonce = os.urandom(12) >>> ct = aesocb.encrypt(nonce, data, aad) >>> aesocb.decrypt(nonce, ct, aad) b'a secret message' .. classmethod:: generate_key(bit_length) Securely generates a random AES-OCB3 key. :param bit_length: The bit length of the key to generate. Must be 128, 192, or 256. :returns bytes: The generated key. .. method:: encrypt(nonce, data, associated_data) .. warning:: Reuse of a ``nonce`` with a given ``key`` compromises the security of any message with that ``nonce`` and ``key`` pair. Encrypts and authenticates the ``data`` provided as well as authenticating the ``associated_data``. The output of this can be passed directly to the ``decrypt`` method. :param nonce: A 12-15 byte value. **NEVER REUSE A NONCE** with a key. :type nonce: :term:`bytes-like` :param data: The data to encrypt. :type data: :term:`bytes-like` :param associated_data: Additional data that should be authenticated with the key, but is not encrypted. Can be ``None``. :type associated_data: :term:`bytes-like` :returns bytes: The ciphertext bytes with the 16 byte tag appended. :raises OverflowError: If ``data`` or ``associated_data`` is larger than 2\ :sup:`31` - 1 bytes. .. method:: decrypt(nonce, data, associated_data) Decrypts the ``data`` and authenticates the ``associated_data``. If you called encrypt with ``associated_data`` you must pass the same ``associated_data`` in decrypt or the integrity check will fail. :param nonce: A 12 byte value. **NEVER REUSE A NONCE** with a key. :type nonce: :term:`bytes-like` :param data: The data to decrypt (with tag appended). :type data: :term:`bytes-like` :param associated_data: Additional data to authenticate. Can be ``None`` if none was passed during encryption. :type associated_data: :term:`bytes-like` :returns bytes: The original plaintext. :raises cryptography.exceptions.InvalidTag: If the authentication tag doesn't validate this exception will be raised. This will occur when the ciphertext has been changed, but will also occur when the key, nonce, or associated data are wrong. .. class:: AESSIV(key) .. versionadded:: 37.0.0 The SIV (synthetic initialization vector) construction is defined in :rfc:`5297`. Depending on how it is used, SIV allows either deterministic authenticated encryption or nonce-based, misuse-resistant authenticated encryption. :param key: A 256, 384, or 512-bit key (double sized from typical AES). This **must** be kept secret. :type key: :term:`bytes-like` :raises cryptography.exceptions.UnsupportedAlgorithm: If the version of OpenSSL does not support AES-SIV. .. doctest:: >>> import os >>> from cryptography.hazmat.primitives.ciphers.aead import AESSIV >>> data = b"a secret message" >>> nonce = os.urandom(16) >>> aad = [b"authenticated but unencrypted data", nonce] >>> key = AESSIV.generate_key(bit_length=512) # AES256 requires 512-bit keys for SIV >>> aessiv = AESSIV(key) >>> ct = aessiv.encrypt(data, aad) >>> aessiv.decrypt(ct, aad) b'a secret message' .. classmethod:: generate_key(bit_length) Securely generates a random AES-SIV key. :param bit_length: The bit length of the key to generate. Must be 256, 384, or 512. AES-SIV splits the key into an encryption and MAC key, so these lengths correspond to AES 128, 192, and 256. :returns bytes: The generated key. .. method:: encrypt(data, associated_data) .. note:: SIV performs nonce-based authenticated encryption when a component of the associated data is a nonce. The final associated data in the list is used for the nonce. Random nonces should have at least 128-bits of entropy. If a nonce is reused with SIV authenticity is retained and confidentiality is only compromised to the extent that an attacker can determine that the same plaintext (and same associated data) was protected with the same nonce and key. If you do not supply a nonce encryption is deterministic and the same (plaintext, key) pair will always produce the same ciphertext. Encrypts and authenticates the ``data`` provided as well as authenticating the ``associated_data``. The output of this can be passed directly to the ``decrypt`` method. :param data: The data to encrypt. :type data: :term:`bytes-like` :param list associated_data: An optional ``list`` of ``bytes-like objects``. This is additional data that should be authenticated with the key, but is not encrypted. Can be ``None``. In SIV mode the final element of this list is treated as a ``nonce``. :returns bytes: The ciphertext bytes with the 16 byte tag **prepended**. :raises OverflowError: If ``data`` or an ``associated_data`` element is larger than 2\ :sup:`31` - 1 bytes. .. method:: decrypt(data, associated_data) Decrypts the ``data`` and authenticates the ``associated_data``. If you called encrypt with ``associated_data`` you must pass the same ``associated_data`` in decrypt or the integrity check will fail. :param bytes data: The data to decrypt (with tag **prepended**). :param list associated_data: An optional ``list`` of ``bytes-like objects``. This is additional data that should be authenticated with the key, but is not encrypted. Can be ``None`` if none was used during encryption. :returns bytes: The original plaintext. :raises cryptography.exceptions.InvalidTag: If the authentication tag doesn't validate this exception will be raised. This will occur when the ciphertext has been changed, but will also occur when the key or associated data are wrong. .. class:: AESCCM(key, tag_length=16) .. versionadded:: 2.0 .. note: AES-CCM is provided largely for compatibility with existing protocols. Due to its construction it is not as computationally efficient as other AEAD ciphers. The AES-CCM construction is composed of the :class:`~cryptography.hazmat.primitives.ciphers.algorithms.AES` block cipher utilizing Counter with CBC-MAC (CCM) (specified in :rfc:`3610`). :param key: A 128, 192, or 256-bit key. This **must** be kept secret. :type key: :term:`bytes-like` :param int tag_length: The length of the authentication tag. This defaults to 16 bytes and it is **strongly** recommended that you do not make it shorter unless absolutely necessary. Valid tag lengths are 4, 6, 8, 10, 12, 14, and 16. :raises cryptography.exceptions.UnsupportedAlgorithm: If the version of OpenSSL does not support AES-CCM. .. doctest:: >>> import os >>> from cryptography.hazmat.primitives.ciphers.aead import AESCCM >>> data = b"a secret message" >>> aad = b"authenticated but unencrypted data" >>> key = AESCCM.generate_key(bit_length=128) >>> aesccm = AESCCM(key) >>> nonce = os.urandom(13) >>> ct = aesccm.encrypt(nonce, data, aad) >>> aesccm.decrypt(nonce, ct, aad) b'a secret message' .. classmethod:: generate_key(bit_length) Securely generates a random AES-CCM key. :param bit_length: The bit length of the key to generate. Must be 128, 192, or 256. :returns bytes: The generated key. .. method:: encrypt(nonce, data, associated_data) .. warning:: Reuse of a ``nonce`` with a given ``key`` compromises the security of any message with that ``nonce`` and ``key`` pair. Encrypts and authenticates the ``data`` provided as well as authenticating the ``associated_data``. The output of this can be passed directly to the ``decrypt`` method. :param nonce: A value of between 7 and 13 bytes. The maximum length is determined by the length of the ciphertext you are encrypting and must satisfy the condition: ``len(data) < 2 ** (8 * (15 - len(nonce)))`` **NEVER REUSE A NONCE** with a key. :type nonce: :term:`bytes-like` :param data: The data to encrypt. :type data: :term:`bytes-like` :param associated_data: Additional data that should be authenticated with the key, but is not encrypted. Can be ``None``. :type associated_data: :term:`bytes-like` :returns bytes: The ciphertext bytes with the tag appended. :raises OverflowError: If ``data`` or ``associated_data`` is larger than 2\ :sup:`31` - 1 bytes. .. method:: decrypt(nonce, data, associated_data) Decrypts the ``data`` and authenticates the ``associated_data``. If you called encrypt with ``associated_data`` you must pass the same ``associated_data`` in decrypt or the integrity check will fail. :param nonce: A value of between 7 and 13 bytes. This is the same value used when you originally called encrypt. **NEVER REUSE A NONCE** with a key. :type nonce: :term:`bytes-like` :param data: The data to decrypt (with tag appended). :type data: :term:`bytes-like` :param associated_data: Additional data to authenticate. Can be ``None`` if none was passed during encryption. :type associated_data: :term:`bytes-like` :returns bytes: The original plaintext. :raises cryptography.exceptions.InvalidTag: If the authentication tag doesn't validate this exception will be raised. This will occur when the ciphertext has been changed, but will also occur when the key, nonce, or associated data are wrong. .. _`recommends a 96-bit IV length`: https://csrc.nist.gov/pubs/sp/800/38/d/final
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