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Edit File: poly1305.py

# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.

from __future__ import absolute_import, division, print_function

from cryptography import utils
from cryptography.exceptions import (
    AlreadyFinalized,
    UnsupportedAlgorithm,
    _Reasons,
)

class Poly1305(object):
    def __init__(self, key):
        from cryptography.hazmat.backends.openssl.backend import backend

if not backend.poly1305_supported():
            raise UnsupportedAlgorithm(
                "poly1305 is not supported by this version of OpenSSL.",
                _Reasons.UNSUPPORTED_MAC,
            )
        self._ctx = backend.create_poly1305_ctx(key)

def update(self, data):
        if self._ctx is None:
            raise AlreadyFinalized("Context was already finalized.")
        utils._check_byteslike("data", data)
        self._ctx.update(data)

def finalize(self):
        if self._ctx is None:
            raise AlreadyFinalized("Context was already finalized.")
        mac = self._ctx.finalize()
        self._ctx = None
        return mac

def verify(self, tag):
        utils._check_bytes("tag", tag)
        if self._ctx is None:
            raise AlreadyFinalized("Context was already finalized.")

ctx, self._ctx = self._ctx, None
        ctx.verify(tag)

@classmethod
    def generate_tag(cls, key, data):
        p = Poly1305(key)
        p.update(data)
        return p.finalize()

@classmethod
    def verify_tag(cls, key, data, tag):
        p = Poly1305(key)
        p.update(data)
        p.verify(tag)

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