mirror of
https://github.com/OpenVPN/openvpn3.git
synced 2024-09-20 12:12:15 +02:00
66 lines
2.0 KiB
C++
66 lines
2.0 KiB
C++
// OpenVPN -- An application to securely tunnel IP networks
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// over a single port, with support for SSL/TLS-based
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// session authentication and key exchange,
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// packet encryption, packet authentication, and
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// packet compression.
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//
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// Copyright (C) 2012-2019 OpenVPN Inc.
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Affero General Public License Version 3
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// as published by the Free Software Foundation.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Affero General Public License for more details.
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//
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// You should have received a copy of the GNU Affero General Public License
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// along with this program in the COPYING file.
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// If not, see <http://www.gnu.org/licenses/>.
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#include <string>
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#include <atomic>
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namespace openvpn {
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namespace crypto {
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// Compare strings in a way that is more resistant to timing attacks.
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// s1 should be the string provided by the user, while s2 is the
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// "secret" string that we are comparing s1 against.
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// Our goal is to prevent timing data from leaking info about the
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// length or content of s2.
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// https://nachtimwald.com/2017/04/02/constant-time-string-comparison-in-c/
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inline bool str_neq(const char *s1, const char *s2)
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{
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unsigned int neq = 0;
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size_t i = 0;
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size_t j = 0;
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size_t k = 0;
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while (true)
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{
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neq |= s1[i] ^ s2[j];
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if (s1[i] == '\0')
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break;
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i++;
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atomic_thread_fence(std::memory_order_acq_rel);
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if (s2[j] != '\0')
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j++;
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atomic_thread_fence(std::memory_order_acq_rel);
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if (s2[j] == '\0')
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k++;
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}
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atomic_thread_fence(std::memory_order_acq_rel);
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return bool(neq);
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}
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inline bool str_neq(const std::string& s1, const std::string& s2)
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{
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return str_neq(s1.c_str(), s2.c_str());
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}
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}
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}
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