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/*
* OpenVPN -- An application to securely tunnel IP networks
* over a single TCP/UDP port, with support for SSL/TLS-based
* session authentication and key exchange,
* packet encryption, packet authentication, and
* packet compression.
*
* Copyright (C) 2010-2026 Sentyron B.V. <openvpn@sentyron.com>
*
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, see <https://www.gnu.org/licenses/>.
*/
/**
* @file
* Data Channel Crypto module documentation file.
*/
/**
* @addtogroup data_crypto Data Channel Crypto module
*
* The Data Channel Crypto Module performs cryptographic operations on
* data channel packets.
*
* @par Security parameters
* This module is merely the user of a VPN tunnel's security parameters.
* It does not perform the negotiation and setup of the security
* parameters, nor the %key generation involved. These actions are done
* by the \link control_processor Control Channel Processor\endlink. This
* module receives the appropriate security parameters from that module in
* the form of a \c crypto_options structure when they are necessary for
* processing a packet.
*
* @par Packet processing functions
* This module receives data channel packets from the \link data_control
* Data Channel Control module\endlink and processes them according to the
* security parameters of the packet's VPN tunnel. The \link data_control
* Data Channel Control module\endlink uses the following interface
* functions:
* - For packets which will be sent to a remote OpenVPN peer:
* - \c tls_pre_encrypt()
* - \c openvpn_encrypt()
* - \c tls_post_encrypt()
* - For packets which have been received from a remote OpenVPN peer:
* - \c tls_pre_decrypt() (documented as part of the \link
* external_multiplexer External Multiplexer\endlink)
* - \c openvpn_decrypt()
*
* @par Settings that control this module's activity
* How the data channel processes packets received from the \link data_control
* Data Channel Control module\endlink at runtime depends on the associated
* \c crypto_options structure. To perform cryptographic operations, the
* \c crypto_options.key_ctx_bi must contain the correct cipher and HMAC
* security parameters for the direction the packet is traveling in.
*
* @par Crypto algorithms
* This module uses the crypto algorithm implementations of the external
* crypto library (currently either OpenSSL (default), or mbed TLS).
*/
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