/* * 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) 2010-2018 Fox Crypto B.V. <openvpn@fox-it.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, write to the Free Software Foundation, Inc., * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. */ /** * @file * Control Channel Processor module documentation file. */ /** * @defgroup control_processor Control Channel Processor module * * This module controls the setup and maintenance of VPN tunnels and the * associated security parameters. * * @par This module's role * The Control Channel Processor module lies at the core of OpenVPN's * activities. It handles the setup of new VPN tunnels, the negotiation * of data channel security parameters, the managing of active VPN * tunnels, and finally the cleanup of expired VPN tunnels. * * @par State structures * A large amount of VPN tunnel state information must be stored within an * OpenVPN process. A wide variety of container structures are used by * this module for that purpose. Several of these structures are listed * below, and the function of the first three VPN tunnel state containers * is described in more detail later. * - VPN tunnel state containers: * - \c tls_multi, security parameter state for a single VPN tunnel. * Contains three instances of the \c tls_session structure. * - \c tls_session, security parameter state of a single session * within a VPN tunnel. Contains two instances of the \c key_state * structure. * - \c key_state, security parameter state of one TLS and data * channel %key set. * - Data channel security parameter containers: * - \c key_ctx_bi, container for two sets of OpenSSL cipher and/or * HMAC context (both directions). Contains two instances of the \c * key_ctx structure. * - \c key_ctx, container for one set of OpenSSL cipher and/or HMAC * context (one directions. * - Key material containers: * - \c key2, container for two sets of cipher and/or HMAC %key * material (both directions). Contains two instances of the \c key * structure. * - \c key, container for one set of cipher and/or HMAC %key material * (one direction). * - \c key_direction_state, ordering of %key material within the \c * key2.key array. * - Key method 2 random material containers: * - \c key_source2, container for both halves of random material used * for %key method 2. Contains two instances of the \c key_source * structure. * - \c key_source, container for one half of random material used for * %key method 2. * * @par The life of a \c tls_multi object * A \c tls_multi structure contains all the security parameter state * information related to the control and data channels of one VPN tunnel. * Its life cycle can be summarized as follows: * -# Initialization: \c tls_multi_init() and \c * tls_multi_init_finalize(), which are called (indirectly) from \c * init_instance() when initializing a new \c context structure. * - Initializes a \c tls_multi structure. * - Allocates the three \c tls_session objects contained by the \c * tls_multi structure, and initializes as appropriate. * -# Management: \c tls_multi_process() and \c tls_pre_decrypt() * - If a new session is initiated by the remote peer, then \c * tls_pre_decrypt() starts the new session negotiation in the * un-trusted \c tls_session. * - If the, as yet, un-trusted \c tls_session authenticates * successfully, then \c tls_multi_process() moves it so as to be * the active \c tls_session. * - If an error occurs during processing of a \c key_state object, * then \c tls_multi_process() cleans up and initializes the * associated \c tls_session object. If the error occurred in the * active \c key_state of the active \c tls_session and the * lame-duck \c key_state of that \c tls_session has not yet * expired, it is preserved as fallback. * -# Cleanup: \c tls_multi_free(), which is called (indirectly) from \c * close_instance() when cleaning up a \c context structure. * - Cleans up a \c tls_multi structure. * - Cleans up the three \c tls_session objects contained by the \c * tls_multi structure. * * @par The life of a \c tls_session object * A \c tls_session structure contains the state information related to an * active and a lame-duck \c key_state. Its life cycle can be summarized * as follows: * -# Initialization: \c tls_session_init() * - Initializes a \c tls_session structure. * - Initializes the primary \c key_state by calling \c * key_state_init(). * -# Renegotiation: \c key_state_soft_reset() * - Cleans up the old lame-duck \c key_state by calling \c * key_state_free(). * - Moves the old primary \c key_state to be the new lame-duck \c * key_state. * - Initializes a new primary \c key_state by calling \c * key_state_init(). * -# Cleanup: \c tls_session_free() * - Cleans up a \c tls_session structure. * - Cleans up all \c key_state objects associated with the session by * calling \c key_state_free() for each. * * @par The life of a \c key_state object * A \c key_state structure represents one control and data channel %key * set. It contains an OpenSSL TLS object that encapsulates the control * channel, and the data channel security parameters needed by the \link * data_crypto Data Channel Crypto module\endlink to perform cryptographic * operations on data channel packets. Its life cycle can be summarized * as follows: * -# Initialization: \c key_state_init() * - Initializes a \c key_state structure. * - Creates a new OpenSSL TLS object to encapsulate this new control * channel session. * - Sets \c key_state.state to \c S_INITIAL. * - Allocates several internal buffers. * - Initializes new reliability layer structures for this key set. * -# Negotiation: \c tls_process() * - The OpenSSL TLS object negotiates a TLS session between itself * and the remote peer's TLS object. * - Key material is generated and exchanged through the TLS session * between OpenVPN peers. * - Both peers initialize their data channel cipher and HMAC key * contexts. * - On successful negotiation, the \c key_state.state will progress * from \c S_INITIAL to \c S_ACTIVE and \c S_NORMAL. * -# Active tunneling: \link data_crypto Data Channel Crypto * module\endlink * - Data channel packet to be sent to a remote OpenVPN peer: * - \c tls_pre_encrypt() loads the security parameters from the \c * key_state into a \c crypto_options structure. * - \c openvpn_encrypt() uses the \c crypto_options to an encrypt * and HMAC sign the data channel packet. * - Data channel packet received from a remote OpenVPN peer: * - \c tls_pre_decrypt() loads the security parameters from the \c * key_state into a \c crypto_options structure. * - \c openvpn_encrypt() uses the \c crypto_options to * authenticate and decrypt the data channel packet. * -# Cleanup: \c key_state_free() * - Cleans up a \c key_state structure together with its OpenSSL TLS * object, key material, internal buffers, and reliability layer * structures. * * @par Control functions * The following two functions drive the Control Channel Processor's * activities. * - \c tls_multi_process(), iterates through the \c tls_session objects * within a given \c tls_multi of a VPN tunnel, and calls \c * tls_process() for each \c tls_session which is being set up, is * already active, or is busy expiring. * - \c tls_process(), performs the Control Channel Processor module's * core handling of received control channel messages, and generates * appropriate messages to be sent. * * @par Functions which control data channel key generation * - Key method 1 key exchange functions: * - \c key_method_1_write(), generates and processes key material to * be sent to the remote OpenVPN peer. * - \c key_method_1_read(), processes key material received from the * remote OpenVPN peer. * - Key method 2 key exchange functions: * - \c key_method_2_write(), generates and processes key material to * be sent to the remote OpenVPN peer. * - \c key_method_2_read(), processes key material received from the * remote OpenVPN peer. */