Danger

This is a “Hazardous Materials” module. You should ONLY use it if you’re 100% absolutely sure that you know what you’re doing because this module is full of land mines, dragons, and dinosaurs with laser guns.

Authenticated encryption¶

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 cryptography.hazmat.primitives.ciphers.aead.ChaCha20Poly1305(key)¶

New in version 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.

Parameters:: key (bytes-like) – A 32-byte key. This must be kept secret.
Raises:: cryptography.exceptions.UnsupportedAlgorithm – If the version of OpenSSL does not support ChaCha20Poly1305.

>>> 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.

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.

Parameters:

nonce (bytes-like) – A 12 byte value. NEVER REUSE A NONCE with a key.
data (bytes) – The data to encrypt.
associated_data (bytes) – Additional data that should be authenticated with the key, but does not need to be encrypted. Can be None.

Returns bytes:

The ciphertext bytes with the 16 byte tag appended.

Raises:

OverflowError – If data or associated_data is larger than 2³¹ - 1 bytes.

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.

Parameters:

nonce (bytes-like) – A 12 byte value. NEVER REUSE A NONCE with a key.
data (bytes) – The data to decrypt (with tag appended).
associated_data (bytes) – Additional data to authenticate. Can be None if none was passed 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, nonce, or associated data are wrong.

class cryptography.hazmat.primitives.ciphers.aead.AESGCM(key)¶

New in version 2.0.

The AES-GCM construction is composed of the AES block cipher utilizing Galois Counter Mode (GCM).

Parameters:: key (bytes-like) – A 128, 192, or 256-bit key. This must be kept secret.

>>> 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.

Parameters:: bit_length – The bit length of the key to generate. Must be 128, 192, or 256.
Returns bytes:: The generated key.

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.

Parameters:

nonce (bytes-like) – NIST recommends a 96-bit IV length for best performance but it can be up to 2⁶⁴ - 1 bits. NEVER REUSE A NONCE with a key.
data (bytes) – The data to encrypt.
associated_data (bytes) – Additional data that should be authenticated with the key, but is not encrypted. Can be None.

Returns bytes:

The ciphertext bytes with the 16 byte tag appended.

Raises:

OverflowError – If data or associated_data is larger than 2³¹ - 1 bytes.

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.

Parameters:

nonce (bytes-like) – NIST recommends a 96-bit IV length for best performance but it can be up to 2⁶⁴ - 1 bits. NEVER REUSE A NONCE with a key.
data (bytes) – The data to decrypt (with tag appended).
associated_data (bytes) – Additional data to authenticate. Can be None if none was passed 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, nonce, or associated data are wrong.

class cryptography.hazmat.primitives.ciphers.aead.AESOCB3(key)¶

New in version 36.0.

The OCB3 construction is defined in RFC 7253. It is an AEAD mode that offers strong integrity guarantees and good performance.

Parameters:: key (bytes-like) – A 128, 192, or 256-bit key. This must be kept secret.
Raises:: cryptography.exceptions.UnsupportedAlgorithm – If the version of OpenSSL does not support AES-OCB3.

>>> 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.

Parameters:: bit_length – The bit length of the key to generate. Must be 128, 192, or 256.
Returns bytes:: The generated key.

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.

Parameters:

nonce (bytes-like) – A 12-15 byte value. NEVER REUSE A NONCE with a key.
data (bytes) – The data to encrypt.
associated_data (bytes) – Additional data that should be authenticated with the key, but is not encrypted. Can be None.

Returns bytes:

The ciphertext bytes with the 16 byte tag appended.

Raises:

OverflowError – If data or associated_data is larger than 2³¹ - 1 bytes.

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.

Parameters:

nonce (bytes-like) – A 12 byte value. NEVER REUSE A NONCE with a key.
data (bytes) – The data to decrypt (with tag appended).
associated_data (bytes) – Additional data to authenticate. Can be None if none was passed 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, nonce, or associated data are wrong.

class cryptography.hazmat.primitives.ciphers.aead.AESSIV(key)¶

New in version 37.0.

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.

Parameters:: key (bytes-like) – A 256, 384, or 512-bit key (double sized from typical AES). This must be kept secret.
Raises:: cryptography.exceptions.UnsupportedAlgorithm – If the version of OpenSSL does not support AES-SIV.

>>> 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.

Parameters:: 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.

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.

Parameters:

data (bytes) – The data to encrypt.
associated_data (list) – An optional list of bytes. 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 2³¹ - 1 bytes.

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.

Parameters:

data (bytes) – The data to decrypt (with tag prepended).
associated_data (list) – An optional list of bytes. 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 cryptography.hazmat.primitives.ciphers.aead.AESCCM(key, tag_length=16)¶

New in version 2.0.

The AES-CCM construction is composed of the AES block cipher utilizing Counter with CBC-MAC (CCM) (specified in RFC 3610).

Parameters:

key (bytes-like) – A 128, 192, or 256-bit key. This must be kept secret.
tag_length (int) – 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.

>>> 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.

Parameters:: bit_length – The bit length of the key to generate. Must be 128, 192, or 256.
Returns bytes:: The generated key.

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.

Parameters:

nonce (bytes-like) – 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.
data (bytes) – The data to encrypt.
associated_data (bytes) – Additional data that should be authenticated with the key, but is not encrypted. Can be None.

Returns bytes:

The ciphertext bytes with the tag appended.

Raises:

OverflowError – If data or associated_data is larger than 2³¹ - 1 bytes.

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.

Parameters:

nonce (bytes-like) – 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.
data (bytes) – The data to decrypt (with tag appended).
associated_data (bytes) – Additional data to authenticate. Can be None if none was passed 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, nonce, or associated data are wrong.