Lib/test/test_hmac.py

import binascii
import functools
import hmac
import hashlib
import unittest
import unittest.mock
import warnings

from test.support import hashlib_helper

from _operator import _compare_digest as operator_compare_digest

try:
    import _hashlib as _hashopenssl
    from _hashlib import HMAC as C_HMAC
    from _hashlib import hmac_new as c_hmac_new
    from _hashlib import compare_digest as openssl_compare_digest
except ImportError:
    _hashopenssl = None
    C_HMAC = None
    c_hmac_new = None
    openssl_compare_digest = None

try:
    import _sha256 as sha256_module
except ImportError:
    sha256_module = None


def ignore_warning(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        with warnings.catch_warnings():
            warnings.filterwarnings("ignore",
                                    category=DeprecationWarning)
            return func(*args, **kwargs)
    return wrapper


class TestVectorsTestCase(unittest.TestCase):

    def assert_hmac_internals(
            self, h, digest, hashname, digest_size, block_size
    ):
        self.assertEqual(h.hexdigest().upper(), digest.upper())
        self.assertEqual(h.digest(), binascii.unhexlify(digest))
        self.assertEqual(h.name, f"hmac-{hashname}")
        self.assertEqual(h.digest_size, digest_size)
        self.assertEqual(h.block_size, block_size)

    def assert_hmac(
        self, key, data, digest, hashfunc, hashname, digest_size, block_size
    ):
        h = hmac.HMAC(key, data, digestmod=hashfunc)
        self.assert_hmac_internals(
            h, digest, hashname, digest_size, block_size
        )

        h = hmac.HMAC(key, data, digestmod=hashname)
        self.assert_hmac_internals(
            h, digest, hashname, digest_size, block_size
        )

        h = hmac.HMAC(key, digestmod=hashname)
        h2 = h.copy()
        h2.update(b"test update")
        h.update(data)
        self.assertEqual(h.hexdigest().upper(), digest.upper())

        h = hmac.new(key, data, digestmod=hashname)
        self.assert_hmac_internals(
            h, digest, hashname, digest_size, block_size
        )

        h = hmac.new(key, None, digestmod=hashname)
        h.update(data)
        self.assertEqual(h.hexdigest().upper(), digest.upper())

        h = hmac.new(key, digestmod=hashname)
        h.update(data)
        self.assertEqual(h.hexdigest().upper(), digest.upper())

        h = hmac.new(key, data, digestmod=hashfunc)
        self.assertEqual(h.hexdigest().upper(), digest.upper())

        self.assertEqual(
            hmac.digest(key, data, digest=hashname),
            binascii.unhexlify(digest)
        )
        self.assertEqual(
            hmac.digest(key, data, digest=hashfunc),
            binascii.unhexlify(digest)
        )

        h = hmac.HMAC.__new__(hmac.HMAC)
        h._init_old(key, data, digestmod=hashname)
        self.assert_hmac_internals(
            h, digest, hashname, digest_size, block_size
        )

        if c_hmac_new is not None:
            h = c_hmac_new(key, data, digestmod=hashname)
            self.assert_hmac_internals(
                h, digest, hashname, digest_size, block_size
            )

            h = c_hmac_new(key, digestmod=hashname)
            h2 = h.copy()
            h2.update(b"test update")
            h.update(data)
            self.assertEqual(h.hexdigest().upper(), digest.upper())

            func = getattr(_hashopenssl, f"openssl_{hashname}")
            h = c_hmac_new(key, data, digestmod=func)
            self.assert_hmac_internals(
                h, digest, hashname, digest_size, block_size
            )

            h = hmac.HMAC.__new__(hmac.HMAC)
            h._init_hmac(key, data, digestmod=hashname)
            self.assert_hmac_internals(
                h, digest, hashname, digest_size, block_size
            )

    @hashlib_helper.requires_hashdigest('md5', openssl=True)
    def test_md5_vectors(self):
        # Test the HMAC module against test vectors from the RFC.

        def md5test(key, data, digest):
            self.assert_hmac(
                key, data, digest,
                hashfunc=hashlib.md5,
                hashname="md5",
                digest_size=16,
                block_size=64
            )

        md5test(b"\x0b" * 16,
                b"Hi There",
                "9294727A3638BB1C13F48EF8158BFC9D")

        md5test(b"Jefe",
                b"what do ya want for nothing?",
                "750c783e6ab0b503eaa86e310a5db738")

        md5test(b"\xaa" * 16,
                b"\xdd" * 50,
                "56be34521d144c88dbb8c733f0e8b3f6")

        md5test(bytes(range(1, 26)),
                b"\xcd" * 50,
                "697eaf0aca3a3aea3a75164746ffaa79")

        md5test(b"\x0C" * 16,
                b"Test With Truncation",
                "56461ef2342edc00f9bab995690efd4c")

        md5test(b"\xaa" * 80,
                b"Test Using Larger Than Block-Size Key - Hash Key First",
                "6b1ab7fe4bd7bf8f0b62e6ce61b9d0cd")

        md5test(b"\xaa" * 80,
                (b"Test Using Larger Than Block-Size Key "
                 b"and Larger Than One Block-Size Data"),
                "6f630fad67cda0ee1fb1f562db3aa53e")

    @hashlib_helper.requires_hashdigest('sha1', openssl=True)
    def test_sha_vectors(self):
        def shatest(key, data, digest):
            self.assert_hmac(
                key, data, digest,
                hashfunc=hashlib.sha1,
                hashname="sha1",
                digest_size=20,
                block_size=64
            )

        shatest(b"\x0b" * 20,
                b"Hi There",
                "b617318655057264e28bc0b6fb378c8ef146be00")

        shatest(b"Jefe",
                b"what do ya want for nothing?",
                "effcdf6ae5eb2fa2d27416d5f184df9c259a7c79")

        shatest(b"\xAA" * 20,
                b"\xDD" * 50,
                "125d7342b9ac11cd91a39af48aa17b4f63f175d3")

        shatest(bytes(range(1, 26)),
                b"\xCD" * 50,
                "4c9007f4026250c6bc8414f9bf50c86c2d7235da")

        shatest(b"\x0C" * 20,
                b"Test With Truncation",
                "4c1a03424b55e07fe7f27be1d58bb9324a9a5a04")

        shatest(b"\xAA" * 80,
                b"Test Using Larger Than Block-Size Key - Hash Key First",
                "aa4ae5e15272d00e95705637ce8a3b55ed402112")

        shatest(b"\xAA" * 80,
                (b"Test Using Larger Than Block-Size Key "
                 b"and Larger Than One Block-Size Data"),
                "e8e99d0f45237d786d6bbaa7965c7808bbff1a91")

    def _rfc4231_test_cases(self, hashfunc, hash_name, digest_size, block_size):
        def hmactest(key, data, hexdigests):
            digest = hexdigests[hashfunc]

            self.assert_hmac(
                key, data, digest,
                hashfunc=hashfunc,
                hashname=hash_name,
                digest_size=digest_size,
                block_size=block_size
            )

        # 4.2.  Test Case 1
        hmactest(key = b'\x0b'*20,
                 data = b'Hi There',
                 hexdigests = {
                   hashlib.sha224: '896fb1128abbdf196832107cd49df33f'
                                   '47b4b1169912ba4f53684b22',
                   hashlib.sha256: 'b0344c61d8db38535ca8afceaf0bf12b'
                                   '881dc200c9833da726e9376c2e32cff7',
                   hashlib.sha384: 'afd03944d84895626b0825f4ab46907f'
                                   '15f9dadbe4101ec682aa034c7cebc59c'
                                   'faea9ea9076ede7f4af152e8b2fa9cb6',
                   hashlib.sha512: '87aa7cdea5ef619d4ff0b4241a1d6cb0'
                                   '2379f4e2ce4ec2787ad0b30545e17cde'
                                   'daa833b7d6b8a702038b274eaea3f4e4'
                                   'be9d914eeb61f1702e696c203a126854',
                 })

        # 4.3.  Test Case 2
        hmactest(key = b'Jefe',
                 data = b'what do ya want for nothing?',
                 hexdigests = {
                   hashlib.sha224: 'a30e01098bc6dbbf45690f3a7e9e6d0f'
                                   '8bbea2a39e6148008fd05e44',
                   hashlib.sha256: '5bdcc146bf60754e6a042426089575c7'
                                   '5a003f089d2739839dec58b964ec3843',
                   hashlib.sha384: 'af45d2e376484031617f78d2b58a6b1b'
                                   '9c7ef464f5a01b47e42ec3736322445e'
                                   '8e2240ca5e69e2c78b3239ecfab21649',
                   hashlib.sha512: '164b7a7bfcf819e2e395fbe73b56e0a3'
                                   '87bd64222e831fd610270cd7ea250554'
                                   '9758bf75c05a994a6d034f65f8f0e6fd'
                                   'caeab1a34d4a6b4b636e070a38bce737',
                 })

        # 4.4.  Test Case 3
        hmactest(key = b'\xaa'*20,
                 data = b'\xdd'*50,
                 hexdigests = {
                   hashlib.sha224: '7fb3cb3588c6c1f6ffa9694d7d6ad264'
                                   '9365b0c1f65d69d1ec8333ea',
                   hashlib.sha256: '773ea91e36800e46854db8ebd09181a7'
                                   '2959098b3ef8c122d9635514ced565fe',
                   hashlib.sha384: '88062608d3e6ad8a0aa2ace014c8a86f'
                                   '0aa635d947ac9febe83ef4e55966144b'
                                   '2a5ab39dc13814b94e3ab6e101a34f27',
                   hashlib.sha512: 'fa73b0089d56a284efb0f0756c890be9'
                                   'b1b5dbdd8ee81a3655f83e33b2279d39'
                                   'bf3e848279a722c806b485a47e67c807'
                                   'b946a337bee8942674278859e13292fb',
                 })

        # 4.5.  Test Case 4
        hmactest(key = bytes(x for x in range(0x01, 0x19+1)),
                 data = b'\xcd'*50,
                 hexdigests = {
                   hashlib.sha224: '6c11506874013cac6a2abc1bb382627c'
                                   'ec6a90d86efc012de7afec5a',
                   hashlib.sha256: '82558a389a443c0ea4cc819899f2083a'
                                   '85f0faa3e578f8077a2e3ff46729665b',
                   hashlib.sha384: '3e8a69b7783c25851933ab6290af6ca7'
                                   '7a9981480850009cc5577c6e1f573b4e'
                                   '6801dd23c4a7d679ccf8a386c674cffb',
                   hashlib.sha512: 'b0ba465637458c6990e5a8c5f61d4af7'
                                   'e576d97ff94b872de76f8050361ee3db'
                                   'a91ca5c11aa25eb4d679275cc5788063'
                                   'a5f19741120c4f2de2adebeb10a298dd',
                 })

        # 4.7.  Test Case 6
        hmactest(key = b'\xaa'*131,
                 data = b'Test Using Larger Than Block-Siz'
                        b'e Key - Hash Key First',
                 hexdigests = {
                   hashlib.sha224: '95e9a0db962095adaebe9b2d6f0dbce2'
                                   'd499f112f2d2b7273fa6870e',
                   hashlib.sha256: '60e431591ee0b67f0d8a26aacbf5b77f'
                                   '8e0bc6213728c5140546040f0ee37f54',
                   hashlib.sha384: '4ece084485813e9088d2c63a041bc5b4'
                                   '4f9ef1012a2b588f3cd11f05033ac4c6'
                                   '0c2ef6ab4030fe8296248df163f44952',
                   hashlib.sha512: '80b24263c7c1a3ebb71493c1dd7be8b4'
                                   '9b46d1f41b4aeec1121b013783f8f352'
                                   '6b56d037e05f2598bd0fd2215d6a1e52'
                                   '95e64f73f63f0aec8b915a985d786598',
                 })

        # 4.8.  Test Case 7
        hmactest(key = b'\xaa'*131,
                 data = b'This is a test using a larger th'
                        b'an block-size key and a larger t'
                        b'han block-size data. The key nee'
                        b'ds to be hashed before being use'
                        b'd by the HMAC algorithm.',
                 hexdigests = {
                   hashlib.sha224: '3a854166ac5d9f023f54d517d0b39dbd'
                                   '946770db9c2b95c9f6f565d1',
                   hashlib.sha256: '9b09ffa71b942fcb27635fbcd5b0e944'
                                   'bfdc63644f0713938a7f51535c3a35e2',
                   hashlib.sha384: '6617178e941f020d351e2f254e8fd32c'
                                   '602420feb0b8fb9adccebb82461e99c5'
                                   'a678cc31e799176d3860e6110c46523e',
                   hashlib.sha512: 'e37b6a775dc87dbaa4dfa9f96e5e3ffd'
                                   'debd71f8867289865df5a32d20cdc944'
                                   'b6022cac3c4982b10d5eeb55c3e4de15'
                                   '134676fb6de0446065c97440fa8c6a58',
                 })

    @hashlib_helper.requires_hashdigest('sha224', openssl=True)
    def test_sha224_rfc4231(self):
        self._rfc4231_test_cases(hashlib.sha224, 'sha224', 28, 64)

    @hashlib_helper.requires_hashdigest('sha256', openssl=True)
    def test_sha256_rfc4231(self):
        self._rfc4231_test_cases(hashlib.sha256, 'sha256', 32, 64)

    @hashlib_helper.requires_hashdigest('sha384', openssl=True)
    def test_sha384_rfc4231(self):
        self._rfc4231_test_cases(hashlib.sha384, 'sha384', 48, 128)

    @hashlib_helper.requires_hashdigest('sha512', openssl=True)
    def test_sha512_rfc4231(self):
        self._rfc4231_test_cases(hashlib.sha512, 'sha512', 64, 128)

    @hashlib_helper.requires_hashdigest('sha256')
    def test_legacy_block_size_warnings(self):
        class MockCrazyHash(object):
            """Ain't no block_size attribute here."""
            def __init__(self, *args):
                self._x = hashlib.sha256(*args)
                self.digest_size = self._x.digest_size
            def update(self, v):
                self._x.update(v)
            def digest(self):
                return self._x.digest()

        with warnings.catch_warnings():
            warnings.simplefilter('error', RuntimeWarning)
            with self.assertRaises(RuntimeWarning):
                hmac.HMAC(b'a', b'b', digestmod=MockCrazyHash)
                self.fail('Expected warning about missing block_size')

            MockCrazyHash.block_size = 1
            with self.assertRaises(RuntimeWarning):
                hmac.HMAC(b'a', b'b', digestmod=MockCrazyHash)
                self.fail('Expected warning about small block_size')

    def test_with_digestmod_no_default(self):
        """The digestmod parameter is required as of Python 3.8."""
        with self.assertRaisesRegex(TypeError, r'required.*digestmod'):
            key = b"\x0b" * 16
            data = b"Hi There"
            hmac.HMAC(key, data, digestmod=None)
        with self.assertRaisesRegex(TypeError, r'required.*digestmod'):
            hmac.new(key, data)
        with self.assertRaisesRegex(TypeError, r'required.*digestmod'):
            hmac.HMAC(key, msg=data, digestmod='')


class ConstructorTestCase(unittest.TestCase):

    expected = (
        "6c845b47f52b3b47f6590c502db7825aad757bf4fadc8fa972f7cd2e76a5bdeb"
    )

    @hashlib_helper.requires_hashdigest('sha256')
    def test_normal(self):
        # Standard constructor call.
        try:
            hmac.HMAC(b"key", digestmod='sha256')
        except Exception:
            self.fail("Standard constructor call raised exception.")

    @hashlib_helper.requires_hashdigest('sha256')
    def test_with_str_key(self):
        # Pass a key of type str, which is an error, because it expects a key
        # of type bytes
        with self.assertRaises(TypeError):
            h = hmac.HMAC("key", digestmod='sha256')

    @hashlib_helper.requires_hashdigest('sha256')
    def test_dot_new_with_str_key(self):
        # Pass a key of type str, which is an error, because it expects a key
        # of type bytes
        with self.assertRaises(TypeError):
            h = hmac.new("key", digestmod='sha256')

    @hashlib_helper.requires_hashdigest('sha256')
    def test_withtext(self):
        # Constructor call with text.
        try:
            h = hmac.HMAC(b"key", b"hash this!", digestmod='sha256')
        except Exception:
            self.fail("Constructor call with text argument raised exception.")
        self.assertEqual(h.hexdigest(), self.expected)

    @hashlib_helper.requires_hashdigest('sha256')
    def test_with_bytearray(self):
        try:
            h = hmac.HMAC(bytearray(b"key"), bytearray(b"hash this!"),
                          digestmod="sha256")
        except Exception:
            self.fail("Constructor call with bytearray arguments raised exception.")
        self.assertEqual(h.hexdigest(), self.expected)

    @hashlib_helper.requires_hashdigest('sha256')
    def test_with_memoryview_msg(self):
        try:
            h = hmac.HMAC(b"key", memoryview(b"hash this!"), digestmod="sha256")
        except Exception:
            self.fail("Constructor call with memoryview msg raised exception.")
        self.assertEqual(h.hexdigest(), self.expected)

    @hashlib_helper.requires_hashdigest('sha256')
    def test_withmodule(self):
        # Constructor call with text and digest module.
        try:
            h = hmac.HMAC(b"key", b"", hashlib.sha256)
        except Exception:
            self.fail("Constructor call with hashlib.sha256 raised exception.")

    @unittest.skipUnless(C_HMAC is not None, 'need _hashlib')
    def test_internal_types(self):
        # internal types like _hashlib.C_HMAC are not constructable
        with self.assertRaisesRegex(
            TypeError, "cannot create 'HMAC' instance"
        ):
            C_HMAC()

    @unittest.skipUnless(sha256_module is not None, 'need _sha256')
    def test_with_sha256_module(self):
        h = hmac.HMAC(b"key", b"hash this!", digestmod=sha256_module.sha256)
        self.assertEqual(h.hexdigest(), self.expected)
        self.assertEqual(h.name, "hmac-sha256")

        digest = hmac.digest(b"key", b"hash this!", sha256_module.sha256)
        self.assertEqual(digest, binascii.unhexlify(self.expected))


class SanityTestCase(unittest.TestCase):

    @hashlib_helper.requires_hashdigest('sha256')
    def test_exercise_all_methods(self):
        # Exercising all methods once.
        # This must not raise any exceptions
        try:
            h = hmac.HMAC(b"my secret key", digestmod="sha256")
            h.update(b"compute the hash of this text!")
            h.digest()
            h.hexdigest()
            h.copy()
        except Exception:
            self.fail("Exception raised during normal usage of HMAC class.")


class CopyTestCase(unittest.TestCase):

    @hashlib_helper.requires_hashdigest('sha256')
    def test_attributes_old(self):
        # Testing if attributes are of same type.
        h1 = hmac.HMAC.__new__(hmac.HMAC)
        h1._init_old(b"key", b"msg", digestmod="sha256")
        h2 = h1.copy()
        self.assertEqual(type(h1._inner), type(h2._inner),
            "Types of inner don't match.")
        self.assertEqual(type(h1._outer), type(h2._outer),
            "Types of outer don't match.")

    @hashlib_helper.requires_hashdigest('sha256')
    def test_realcopy_old(self):
        # Testing if the copy method created a real copy.
        h1 = hmac.HMAC.__new__(hmac.HMAC)
        h1._init_old(b"key", b"msg", digestmod="sha256")
        h2 = h1.copy()
        # Using id() in case somebody has overridden __eq__/__ne__.
        self.assertTrue(id(h1) != id(h2), "No real copy of the HMAC instance.")
        self.assertTrue(id(h1._inner) != id(h2._inner),
            "No real copy of the attribute 'inner'.")
        self.assertTrue(id(h1._outer) != id(h2._outer),
            "No real copy of the attribute 'outer'.")
        self.assertIs(h1._hmac, None)

    @unittest.skipIf(_hashopenssl is None, "test requires _hashopenssl")
    @hashlib_helper.requires_hashdigest('sha256')
    def test_realcopy_hmac(self):
        h1 = hmac.HMAC.__new__(hmac.HMAC)
        h1._init_hmac(b"key", b"msg", digestmod="sha256")
        h2 = h1.copy()
        self.assertTrue(id(h1._hmac) != id(h2._hmac))

    @hashlib_helper.requires_hashdigest('sha256')
    def test_equality(self):
        # Testing if the copy has the same digests.
        h1 = hmac.HMAC(b"key", digestmod="sha256")
        h1.update(b"some random text")
        h2 = h1.copy()
        self.assertEqual(h1.digest(), h2.digest(),
            "Digest of copy doesn't match original digest.")
        self.assertEqual(h1.hexdigest(), h2.hexdigest(),
            "Hexdigest of copy doesn't match original hexdigest.")

    @hashlib_helper.requires_hashdigest('sha256')
    def test_equality_new(self):
        # Testing if the copy has the same digests with hmac.new().
        h1 = hmac.new(b"key", digestmod="sha256")
        h1.update(b"some random text")
        h2 = h1.copy()
        self.assertTrue(
            id(h1) != id(h2), "No real copy of the HMAC instance."
        )
        self.assertEqual(h1.digest(), h2.digest(),
            "Digest of copy doesn't match original digest.")
        self.assertEqual(h1.hexdigest(), h2.hexdigest(),
            "Hexdigest of copy doesn't match original hexdigest.")


class CompareDigestTestCase(unittest.TestCase):

    def test_hmac_compare_digest(self):
        self._test_compare_digest(hmac.compare_digest)
        if openssl_compare_digest is not None:
            self.assertIs(hmac.compare_digest, openssl_compare_digest)
        else:
            self.assertIs(hmac.compare_digest, operator_compare_digest)

    def test_operator_compare_digest(self):
        self._test_compare_digest(operator_compare_digest)

    @unittest.skipIf(openssl_compare_digest is None, "test requires _hashlib")
    def test_openssl_compare_digest(self):
        self._test_compare_digest(openssl_compare_digest)

    def _test_compare_digest(self, compare_digest):
        # Testing input type exception handling
        a, b = 100, 200
        self.assertRaises(TypeError, compare_digest, a, b)
        a, b = 100, b"foobar"
        self.assertRaises(TypeError, compare_digest, a, b)
        a, b = b"foobar", 200
        self.assertRaises(TypeError, compare_digest, a, b)
        a, b = "foobar", b"foobar"
        self.assertRaises(TypeError, compare_digest, a, b)
        a, b = b"foobar", "foobar"
        self.assertRaises(TypeError, compare_digest, a, b)

        # Testing bytes of different lengths
        a, b = b"foobar", b"foo"
        self.assertFalse(compare_digest(a, b))
        a, b = b"\xde\xad\xbe\xef", b"\xde\xad"
        self.assertFalse(compare_digest(a, b))

        # Testing bytes of same lengths, different values
        a, b = b"foobar", b"foobaz"
        self.assertFalse(compare_digest(a, b))
        a, b = b"\xde\xad\xbe\xef", b"\xab\xad\x1d\xea"
        self.assertFalse(compare_digest(a, b))

        # Testing bytes of same lengths, same values
        a, b = b"foobar", b"foobar"
        self.assertTrue(compare_digest(a, b))
        a, b = b"\xde\xad\xbe\xef", b"\xde\xad\xbe\xef"
        self.assertTrue(compare_digest(a, b))

        # Testing bytearrays of same lengths, same values
        a, b = bytearray(b"foobar"), bytearray(b"foobar")
        self.assertTrue(compare_digest(a, b))

        # Testing bytearrays of different lengths
        a, b = bytearray(b"foobar"), bytearray(b"foo")
        self.assertFalse(compare_digest(a, b))

        # Testing bytearrays of same lengths, different values
        a, b = bytearray(b"foobar"), bytearray(b"foobaz")
        self.assertFalse(compare_digest(a, b))

        # Testing byte and bytearray of same lengths, same values
        a, b = bytearray(b"foobar"), b"foobar"
        self.assertTrue(compare_digest(a, b))
        self.assertTrue(compare_digest(b, a))

        # Testing byte bytearray of different lengths
        a, b = bytearray(b"foobar"), b"foo"
        self.assertFalse(compare_digest(a, b))
        self.assertFalse(compare_digest(b, a))

        # Testing byte and bytearray of same lengths, different values
        a, b = bytearray(b"foobar"), b"foobaz"
        self.assertFalse(compare_digest(a, b))
        self.assertFalse(compare_digest(b, a))

        # Testing str of same lengths
        a, b = "foobar", "foobar"
        self.assertTrue(compare_digest(a, b))

        # Testing str of different lengths
        a, b = "foo", "foobar"
        self.assertFalse(compare_digest(a, b))

        # Testing bytes of same lengths, different values
        a, b = "foobar", "foobaz"
        self.assertFalse(compare_digest(a, b))

        # Testing error cases
        a, b = "foobar", b"foobar"
        self.assertRaises(TypeError, compare_digest, a, b)
        a, b = b"foobar", "foobar"
        self.assertRaises(TypeError, compare_digest, a, b)
        a, b = b"foobar", 1
        self.assertRaises(TypeError, compare_digest, a, b)
        a, b = 100, 200
        self.assertRaises(TypeError, compare_digest, a, b)
        a, b = "fooä", "fooä"
        self.assertRaises(TypeError, compare_digest, a, b)

        # subclasses are supported by ignore __eq__
        class mystr(str):
            def __eq__(self, other):
                return False

        a, b = mystr("foobar"), mystr("foobar")
        self.assertTrue(compare_digest(a, b))
        a, b = mystr("foobar"), "foobar"
        self.assertTrue(compare_digest(a, b))
        a, b = mystr("foobar"), mystr("foobaz")
        self.assertFalse(compare_digest(a, b))

        class mybytes(bytes):
            def __eq__(self, other):
                return False

        a, b = mybytes(b"foobar"), mybytes(b"foobar")
        self.assertTrue(compare_digest(a, b))
        a, b = mybytes(b"foobar"), b"foobar"
        self.assertTrue(compare_digest(a, b))
        a, b = mybytes(b"foobar"), mybytes(b"foobaz")
        self.assertFalse(compare_digest(a, b))


if __name__ == "__main__":
    unittest.main()