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# vim: tabstop=4 shiftwidth=4 softtabstop=4
# Copyright 2011 OpenStack LLC.
# All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
"""
Authentication related utilities and helper functions.
"""
def auth_str_equal(provided, known):
"""Constant-time string comparison.
:params provided: the first string
:params known: the second string
:return: True if the strings are equal.
This function takes two strings and compares them. It is intended to be
used when doing a comparison for authentication purposes to help guard
against timing attacks. When using the function for this purpose, always
provide the user-provided password as the first argument. The time this
function will take is always a factor of the length of this string.
"""
result = 0
p_len = len(provided)
k_len = len(known)
for i in xrange(p_len):
a = ord(provided[i]) if i < p_len else 0
b = ord(known[i]) if i < k_len else 0
result |= a ^ b
return (p_len == k_len) & (result == 0)
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