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# 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 cryptography import utils from cryptography.exceptions import ( AlreadyFinalized, UnsupportedAlgorithm, _Reasons, ) from cryptography.hazmat.backends import _get_backend from cryptography.hazmat.backends.interfaces import HMACBackend from cryptography.hazmat.primitives import hashes class HMAC(hashes.HashContext): def __init__( self, key: bytes, algorithm: hashes.HashAlgorithm, backend=None, ctx=None, ): backend = _get_backend(backend) if not isinstance(backend, HMACBackend): raise UnsupportedAlgorithm( "Backend object does not implement HMACBackend.", _Reasons.BACKEND_MISSING_INTERFACE, ) if not isinstance(algorithm, hashes.HashAlgorithm): raise TypeError("Expected instance of hashes.HashAlgorithm.") self._algorithm = algorithm self._backend = backend self._key = key if ctx is None: self._ctx = self._backend.create_hmac_ctx(key, self.algorithm) else: self._ctx = ctx algorithm = utils.read_only_property("_algorithm") def update(self, data: bytes) -> None: if self._ctx is None: raise AlreadyFinalized("Context was already finalized.") utils._check_byteslike("data", data) self._ctx.update(data) def copy(self) -> "HMAC": if self._ctx is None: raise AlreadyFinalized("Context was already finalized.") return HMAC( self._key, self.algorithm, backend=self._backend, ctx=self._ctx.copy(), ) def finalize(self) -> bytes: if self._ctx is None: raise AlreadyFinalized("Context was already finalized.") digest = self._ctx.finalize() self._ctx = None return digest def verify(self, signature: bytes) -> None: utils._check_bytes("signature", signature) if self._ctx is None: raise AlreadyFinalized("Context was already finalized.") ctx, self._ctx = self._ctx, None ctx.verify(signature)