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constant-time.rst	1592	0644	editdlrm
cryptographic-hashes.rst	9153	0644	editdlrm
index.rst	246	0644	editdlrm
key-derivation-functions.rst	39929	0644	editdlrm
keywrap.rst	3116	0644	editdlrm
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symmetric-encryption.rst	31500	0644	editdlrm
twofactor.rst	10562	0644	editdlrm

.. hazmat:: Constant time functions ======================= .. currentmodule:: cryptography.hazmat.primitives.constant_time This module contains functions for operating with secret data in a way that does not leak information about that data through how long it takes to perform the operation. These functions should be used whenever operating on secret data along with data that is user supplied. An example would be comparing a HMAC signature received from a client to the one generated by the server code for authentication purposes. For more information about this sort of issue, see `Coda Hale's blog post`_ about the timing attacks on KeyCzar and Java's ``MessageDigest.isEqual()``. .. function:: bytes_eq(a, b) Compares ``a`` and ``b`` with one another. If ``a`` and ``b`` have different lengths, this returns ``False`` immediately. Otherwise it compares them in a way that takes the same amount of time, regardless of how many characters are the same between the two. .. doctest:: >>> from cryptography.hazmat.primitives import constant_time >>> constant_time.bytes_eq(b"foo", b"foo") True >>> constant_time.bytes_eq(b"foo", b"bar") False :param bytes a: The left-hand side. :param bytes b: The right-hand side. :returns bool: ``True`` if ``a`` has the same bytes as ``b``, otherwise ``False``. :raises TypeError: This exception is raised if ``a`` or ``b`` is not ``bytes``. .. _`Coda Hale's blog post`: https://codahale.com/a-lesson-in-timing-attacks/