# 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.exceptions import InvalidSignature from cryptography.hazmat.primitives import constant_time _POLY1305_TAG_SIZE = 16 _POLY1305_KEY_SIZE = 32 class _Poly1305Context(object): def __init__(self, backend, key): self._backend = backend key_ptr = self._backend._ffi.from_buffer(key) # This function copies the key into OpenSSL-owned memory so we don't # need to retain it ourselves evp_pkey = self._backend._lib.EVP_PKEY_new_raw_private_key( self._backend._lib.NID_poly1305, self._backend._ffi.NULL, key_ptr, len(key), ) self._backend.openssl_assert(evp_pkey != self._backend._ffi.NULL) self._evp_pkey = self._backend._ffi.gc( evp_pkey, self._backend._lib.EVP_PKEY_free ) ctx = self._backend._lib.Cryptography_EVP_MD_CTX_new() self._backend.openssl_assert(ctx != self._backend._ffi.NULL) self._ctx = self._backend._ffi.gc( ctx, self._backend._lib.Cryptography_EVP_MD_CTX_free ) res = self._backend._lib.EVP_DigestSignInit( self._ctx, self._backend._ffi.NULL, self._backend._ffi.NULL, self._backend._ffi.NULL, self._evp_pkey, ) self._backend.openssl_assert(res == 1) def update(self, data): data_ptr = self._backend._ffi.from_buffer(data) res = self._backend._lib.EVP_DigestSignUpdate( self._ctx, data_ptr, len(data) ) self._backend.openssl_assert(res != 0) def finalize(self): buf = self._backend._ffi.new("unsigned char[]", _POLY1305_TAG_SIZE) outlen = self._backend._ffi.new("size_t *") res = self._backend._lib.EVP_DigestSignFinal(self._ctx, buf, outlen) self._backend.openssl_assert(res != 0) self._backend.openssl_assert(outlen[0] == _POLY1305_TAG_SIZE) return self._backend._ffi.buffer(buf)[: outlen[0]] def verify(self, tag): mac = self.finalize() if not constant_time.bytes_eq(mac, tag): raise InvalidSignature("Value did not match computed tag.")