mirror of
https://github.com/OpenVPN/openvpn3.git
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16b10559f2
OpenVPN Technologies, Inc. change their name to OpenVPN Inc. during the autumn of 2017. Signed-off-by: David Sommerseth <davids@openvpn.net>
141 lines
4.0 KiB
C++
141 lines
4.0 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) 2012-2017 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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// General-purpose OpenVPN protocol decrypt method (CBC/HMAC) that is independent of the underlying CRYPTO_API
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#ifndef OPENVPN_CRYPTO_DECRYPT_CHM_H
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#define OPENVPN_CRYPTO_DECRYPT_CHM_H
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#include <cstring>
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#include <openvpn/common/size.hpp>
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#include <openvpn/common/exception.hpp>
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#include <openvpn/common/memneq.hpp>
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#include <openvpn/buffer/buffer.hpp>
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#include <openvpn/frame/frame.hpp>
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#include <openvpn/crypto/cipher.hpp>
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#include <openvpn/crypto/ovpnhmac.hpp>
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#include <openvpn/crypto/static_key.hpp>
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#include <openvpn/crypto/packet_id.hpp>
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#include <openvpn/log/sessionstats.hpp>
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namespace openvpn {
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template <typename CRYPTO_API>
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class DecryptCHM {
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public:
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OPENVPN_SIMPLE_EXCEPTION(chm_unsupported_cipher_mode);
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Error::Type decrypt(BufferAllocated& buf, const PacketID::time_t now)
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{
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// skip null packets
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if (!buf.size())
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return Error::SUCCESS;
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// verify the HMAC
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if (hmac.defined())
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{
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unsigned char local_hmac[CRYPTO_API::HMACContext::MAX_HMAC_SIZE];
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const size_t hmac_size = hmac.output_size();
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const unsigned char *packet_hmac = buf.read_alloc(hmac_size);
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hmac.hmac(local_hmac, hmac_size, buf.c_data(), buf.size());
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if (crypto::memneq(local_hmac, packet_hmac, hmac_size))
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{
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buf.reset_size();
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return Error::HMAC_ERROR;
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}
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}
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// decrypt packet ID + payload
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if (cipher.defined())
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{
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unsigned char iv_buf[CRYPTO_API::CipherContext::MAX_IV_LENGTH];
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const size_t iv_length = cipher.iv_length();
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// extract IV from head of packet
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buf.read(iv_buf, iv_length);
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// initialize work buffer
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frame->prepare(Frame::DECRYPT_WORK, work);
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// decrypt from buf -> work
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const size_t decrypt_bytes = cipher.decrypt(iv_buf, work.data(), work.max_size(), buf.c_data(), buf.size());
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if (!decrypt_bytes)
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{
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buf.reset_size();
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return Error::DECRYPT_ERROR;
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}
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work.set_size(decrypt_bytes);
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// handle different cipher modes
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const int cipher_mode = cipher.cipher_mode();
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if (cipher_mode == CRYPTO_API::CipherContext::CIPH_CBC_MODE)
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{
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if (!verify_packet_id(work, now))
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{
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buf.reset_size();
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return Error::REPLAY_ERROR;
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}
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}
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else
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{
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throw chm_unsupported_cipher_mode();
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}
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// return cleartext result in buf
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buf.swap(work);
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}
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else // no encryption
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{
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if (!verify_packet_id(buf, now))
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{
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buf.reset_size();
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return Error::REPLAY_ERROR;
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}
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}
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return Error::SUCCESS;
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}
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Frame::Ptr frame;
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CipherContext<CRYPTO_API> cipher;
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OvpnHMAC<CRYPTO_API> hmac;
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PacketIDReceive pid_recv;
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private:
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bool verify_packet_id(BufferAllocated& buf, const PacketID::time_t now)
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{
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// ignore packet ID if pid_recv is not initialized
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if (pid_recv.initialized())
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{
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const PacketID pid = pid_recv.read_next(buf);
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if (!pid_recv.test_add(pid, now, true)) // verify packet ID
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return false;
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}
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return true;
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}
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BufferAllocated work;
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};
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} // namespace openvpn
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#endif // OPENVPN_CRYPTO_DECRYPT_H
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