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.

Poly1305¶

Poly1305 is an authenticator that takes a 32-byte key and a message and produces a 16-byte tag. This tag is used to authenticate the message. Each key must only be used once. Using the same key to generate tags for multiple messages allows an attacker to forge tags. Poly1305 is described in RFC 7539.

class cryptography.hazmat.primitives.poly1305.Poly1305(key)¶

New in version 2.7.

Warning

Using the same key to generate tags for multiple messages allows an attacker to forge tags. Always generate a new key per message you want to authenticate. If you are using this as a MAC for symmetric encryption please use ChaCha20Poly1305 instead.

>>> from cryptography.hazmat.primitives import poly1305
>>> p = poly1305.Poly1305(key)
>>> p.update(b"message to authenticate")
>>> p.finalize()
b'T\xae\xff3\xbdW\xef\xd5r\x01\xe2n=\xb7\xd2h'

To check that a given tag is correct use the verify() method. You will receive an exception if the tag is wrong:

>>> p = poly1305.Poly1305(key)
>>> p.update(b"message to authenticate")
>>> p.verify(b"an incorrect tag")
Traceback (most recent call last):
...
cryptography.exceptions.InvalidSignature: Value did not match computed tag.

Parameters:: key (bytes-like) – Secret key as bytes.
Raises:: cryptography.exceptions.UnsupportedAlgorithm – This is raised if the version of OpenSSL cryptography is compiled against does not support this algorithm.

update(data)¶

Parameters:

data (bytes-like) – The bytes to hash and authenticate.

Raises:

cryptography.exceptions.AlreadyFinalized – See finalize()
TypeError – This exception is raised if data is not bytes.

verify(tag)¶

Finalize the current context and securely compare the MAC to tag.

Parameters:

tag (bytes) – The bytes to compare against.

Raises:

cryptography.exceptions.AlreadyFinalized – See finalize()
cryptography.exceptions.InvalidSignature – If tag does not match.
TypeError – This exception is raised if tag is not bytes.

finalize()¶

Finalize the current context and return the message authentication code as bytes.

After finalize has been called this object can no longer be used and update(), verify(), and finalize() will raise an AlreadyFinalized exception.

Return bytes:: The message authentication code as bytes.
Raises:: cryptography.exceptions.AlreadyFinalized –

classmethod generate_tag(key, data)¶

A single step alternative to do sign operations. Returns the message authentication code as bytes for the given key and data.

Parameters:

key (bytes-like) – Secret key as bytes.
data (bytes-like) – The bytes to hash and authenticate.

Return bytes:

The message authentication code as bytes.

Raises:

cryptography.exceptions.UnsupportedAlgorithm – This is raised if the version of OpenSSL cryptography is compiled against does not support this algorithm.
TypeError – This exception is raised if key or data are not bytes.

>>> poly1305.Poly1305.generate_tag(key, b"message to authenticate")
b'T\xae\xff3\xbdW\xef\xd5r\x01\xe2n=\xb7\xd2h'

classmethod verify_tag(key, data, tag)¶

A single step alternative to do verify operations. Securely compares the MAC to tag, using the given key and data.

Parameters:

key (bytes-like) – Secret key as bytes.
data (bytes-like) – The bytes to hash and authenticate.
tag (bytes) – The bytes to compare against.

Raises:

cryptography.exceptions.UnsupportedAlgorithm – This is raised if the version of OpenSSL cryptography is compiled against does not support this algorithm.
TypeError – This exception is raised if key, data or tag are not bytes.
cryptography.exceptions.InvalidSignature – If tag does not match.

>>> poly1305.Poly1305.verify_tag(key, b"message to authenticate", b"an incorrect tag")
Traceback (most recent call last):
...
cryptography.exceptions.InvalidSignature: Value did not match computed tag.