path: root/src/openvpn/crypto.h

/*
 *  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) 2002-2010 OpenVPN Technologies, Inc. <sales@openvpn.net>
 *  Copyright (C) 2010-2014 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 (see the file COPYING included with this
 *  distribution); if not, write to the Free Software Foundation, Inc.,
 *  59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

/**
 * @file Data Channel Cryptography Module
 *
 * @addtogroup data_crypto Data Channel Crypto module
 *
 * @par Crypto packet formats
 * The Data Channel Crypto module supports a number of crypto modes and
 * configurable options. The actual packet format depends on these options. A
 * Data Channel packet can consist of:
 *  - \b Opcode, one byte specifying the packet type (see @ref network_protocol
 *    "Network protocol").
 *  - \b Peer-id, if using the v2 data channel packet format (see @ref
 *    network_protocol "Network protocol").
 *  - \b HMAC, covering the ciphertext IV + ciphertext. The HMAC size depends
 *    on the \c \-\-auth option. If \c \-\-auth \c none is specified, there is no
 *    HMAC at all.
 *  - \b Ciphertext \b IV, if not disabled by \c \-\-no-iv. The IV size depends on
 *    the \c \-\-cipher option.
 *  - \b Packet \b ID, a 32-bit incrementing packet counter that provides replay
 *    protection (if not disabled by \c \-\-no-replay).
 *  - \b Timestamp, a 32-bit timestamp of the current time.
 *  - \b Payload, the plain text network packet to be encrypted (unless
 *    encryption is disabled by using \c \-\-cipher \c none). The payload might
 *    already be compressed (see @ref compression "Compression module").
 *
 * @par
 * This section does not discuss the opcode and peer-id, since those do not
 * depend on the data channel crypto. See @ref network_protocol
 * "Network protocol" for more information on those.
 *
 * @par
 * \e Legenda \n
 * <tt>[ xxx ]</tt> = unprotected \n
 * <tt>[ - xxx - ]</tt> = authenticated \n
 * <tt>[ * xxx * ]</tt> = encrypted and authenticated
 *
 * @par
 * <b>CBC data channel cypto format</b> \n
 * In CBC mode, both TLS-mode and static key mode are supported. The IV
 * consists of random bits to provide unpredictable IVs. \n
 * <i>CBC IV format:</i> \n
 * <tt> [ - random - ] </tt> \n
 * <i>CBC data channel crypto format in TLS-mode:</i> \n
 * <tt> [ HMAC ] [ - IV - ] [ * packet ID * ] [ * packet payload * ] </tt> \n
 * <i>CBC data channel crypto format in static key mode:</i> \n
 * <tt> [ HMAC ] [ - IV - ] [ * packet ID * ] [ * timestamp * ]
 * [ * packet payload * ] </tt>
 *
 * @par
 * <b>CFB/OFB data channel crypto format</b> \n
 * CFB and OFB modes are only supported in TLS mode. In these modes, the IV
 * consists of the packet counter and a timestamp. If the IV is more than 8
 * bytes long, the remaining space is filled with zeroes. The packet counter may
 * not roll over within a single TLS sessions. This results in a unique IV for
 * each packet, as required by the CFB and OFB cipher modes.
 *
 * @par
 * <i>CFB/OFB IV format:</i> \n
 * <tt>   [ - packet ID - ] [ - timestamp - ] [ - opt: zero-padding - ] </tt>\n
 * <i>CFB/OFB data channel crypto format:</i> \n
 * <tt>   [ HMAC ] [ - IV - ] [ * packet payload * ] </tt>
 *
 * @par
 * <b>No-crypto data channel format</b> \n
 * In no-crypto mode (\c \-\-cipher \c none is specified), both TLS-mode and
 * static key mode are supported. No encryption will be performed on the packet,
 * but packets can still be authenticated. This mode does not require an IV.\n
 * <i>No-crypto data channel crypto format in TLS-mode:</i> \n
 * <tt> [ HMAC ] [ - packet ID - ] [ - packet payload - ] </tt> \n
 * <i>No-crypto data channel crypto format in static key mode:</i> \n
 * <tt> [ HMAC ] [ - packet ID - ] [ - timestamp - ] [ - packet payload - ] </tt>
 *
 */

#ifndef CRYPTO_H
#define CRYPTO_H

#ifdef ENABLE_CRYPTO

#include "crypto_backend.h"
#include "basic.h"
#include "buffer.h"
#include "packet_id.h"
#include "mtu.h"

/** Wrapper struct to pass around MD5 digests */
struct md5_digest {
  uint8_t digest[MD5_DIGEST_LENGTH];
};

/*
 * Defines a key type and key length for both cipher and HMAC.
 */
struct key_type
{
  uint8_t cipher_length; 	/**< Cipher length, in bytes */
  uint8_t hmac_length;		/**< HMAC length, in bytes */
  const cipher_kt_t *cipher;	/**< Cipher static parameters */
  const md_kt_t *digest;	/**< Message digest static parameters */
};

/**
 * Container for unidirectional cipher and HMAC %key material.
 * @ingroup control_processor
 */
struct key
{
  uint8_t cipher[MAX_CIPHER_KEY_LENGTH];
                                /**< %Key material for cipher operations. */
  uint8_t hmac[MAX_HMAC_KEY_LENGTH];
                                /**< %Key material for HMAC operations. */
};


/**
 * Container for one set of OpenSSL cipher and/or HMAC contexts.
 * @ingroup control_processor
 */
struct key_ctx
{
  cipher_ctx_t *cipher;      	/**< Generic cipher %context. */
  hmac_ctx_t *hmac;               /**< Generic HMAC %context. */
};

#define KEY_DIRECTION_BIDIRECTIONAL 0 /* same keys for both directions */
#define KEY_DIRECTION_NORMAL        1 /* encrypt with keys[0], decrypt with keys[1] */
#define KEY_DIRECTION_INVERSE       2 /* encrypt with keys[1], decrypt with keys[0] */

/**
 * Container for bidirectional cipher and HMAC %key material.
 * @ingroup control_processor
 */
struct key2
{
  int n;                        /**< The number of \c key objects stored
                                 *   in the \c key2.keys array. */
  struct key keys[2];           /**< Two unidirectional sets of %key
                                 *   material. */
};

/**
 * %Key ordering of the \c key2.keys array.
 * @ingroup control_processor
 *
 * This structure takes care of correct ordering when using unidirectional
 * or bidirectional %key material, and allows the same shared secret %key
 * file to be loaded in the same way by client and server by having one of
 * the hosts use an reversed ordering.
 */
struct key_direction_state
{
  int out_key;                  /**< Index into the \c key2.keys array for
                                 *   the sending direction. */
  int in_key;                   /**< Index into the \c key2.keys array for
                                 *   the receiving direction. */
  int need_keys;                /**< The number of key objects necessary
                                 *   to support both sending and
                                 *   receiving.
                                 *
                                 *   This will be 1 if the same keys are
                                 *   used in both directions, or 2 if
                                 *   there are two sets of unidirectional
                                 *   keys. */
};

/**
 * Container for two sets of OpenSSL cipher and/or HMAC contexts for both
 * sending and receiving directions.
 * @ingroup control_processor
 */
struct key_ctx_bi
{
  struct key_ctx encrypt;       /**< OpenSSL cipher and/or HMAC contexts
                                 *   for sending direction. */
  struct key_ctx decrypt;       /**< OpenSSL cipher and/or HMAC contexts
                                 *   for receiving direction. */
};

/**
 * Security parameter state for processing data channel packets.
 * @ingroup data_crypto
 */
struct crypto_options
{
  struct key_ctx_bi *key_ctx_bi;
                                /**< OpenSSL cipher and HMAC contexts for
                                 *   both sending and receiving
                                 *   directions. */
  struct packet_id *packet_id;  /**< Current packet ID state for both
                                 *   sending and receiving directions. */
  struct packet_id_persist *pid_persist;
                                /**< Persistent packet ID state for
                                 *   keeping state between successive
                                 *   OpenVPN process startups. */

# define CO_PACKET_ID_LONG_FORM  (1<<0)
                                /**< Bit-flag indicating whether to use
                                 *   OpenVPN's long packet ID format. */
# define CO_USE_IV               (1<<1)
                                /**< Bit-flag indicating whether to
                                 *   generate a pseudo-random IV for each
                                 *   packet being encrypted. */
# define CO_IGNORE_PACKET_ID     (1<<2)
                                /**< Bit-flag indicating whether to ignore
                                 *   the packet ID of a received packet.
                                 *   This flag is used during processing
                                 *   of the first packet received from a
                                 *   client. */
# define CO_MUTE_REPLAY_WARNINGS (1<<3)
                                /**< Bit-flag indicating not to display
                                 *   replay warnings. */
  unsigned int flags;           /**< Bit-flags determining behavior of
                                 *   security operation functions. */
};

#define RKF_MUST_SUCCEED (1<<0)
#define RKF_INLINE       (1<<1)
void read_key_file (struct key2 *key2, const char *file, const unsigned int flags);

int write_key_file (const int nkeys, const char *filename);

int read_passphrase_hash (const char *passphrase_file,
			  const md_kt_t *digest,
			  uint8_t *output,
			  int len);

void generate_key_random (struct key *key, const struct key_type *kt);

void check_replay_iv_consistency(const struct key_type *kt, bool packet_id, bool use_iv);

bool check_key (struct key *key, const struct key_type *kt);

void fixup_key (struct key *key, const struct key_type *kt);

bool write_key (const struct key *key, const struct key_type *kt,
		struct buffer *buf);

int read_key (struct key *key, const struct key_type *kt, struct buffer *buf);

void init_key_type (struct key_type *kt, const char *ciphername,
    bool ciphername_defined, const char *authname, bool authname_defined,
    int keysize, bool cfb_ofb_allowed, bool warn);

/*
 * Key context functions
 */

void init_key_ctx (struct key_ctx *ctx, struct key *key,
		   const struct key_type *kt, int enc,
		   const char *prefix);

void free_key_ctx (struct key_ctx *ctx);

void free_key_ctx_bi (struct key_ctx_bi *ctx);


/**************************************************************************/
/** @name Functions for performing security operations on data channel packets
 *  @{ */

/**
 * Encrypt and HMAC sign a packet so that it can be sent as a data channel
 * VPN tunnel packet to a remote OpenVPN peer.
 * @ingroup data_crypto
 *
 * This function handles encryption and HMAC signing of a data channel
 * packet before it is sent to its remote OpenVPN peer.  It receives the
 * necessary security parameters in the \a opt argument, which should have
 * been set to the correct values by the \c tls_pre_encrypt() function.
 *
 * This function calls the \c EVP_Cipher* and \c HMAC_* functions of the
 * OpenSSL library to perform the actual security operations.
 *
 * If an error occurs during processing, then the \a buf %buffer is set to
 * empty.
 *
 * @param buf          - The %buffer containing the packet on which to
 *                       perform security operations.
 * @param work         - A working %buffer.
 * @param opt          - The security parameter state for this VPN tunnel.
 * @param frame        - The packet geometry parameters for this VPN
 *                       tunnel.
 * @return This function returns void.\n On return, the \a buf argument
 *     will point to the resulting %buffer.  This %buffer will either
 *     contain the processed packet ready for sending, or be empty if an
 *     error occurred.
 */
void openvpn_encrypt (struct buffer *buf, struct buffer work,
		      const struct crypto_options *opt,
		      const struct frame* frame);


/**
 * HMAC verify and decrypt a data channel packet received from a remote
 * OpenVPN peer.
 * @ingroup data_crypto
 *
 * This function handles authenticating and decrypting a data channel
 * packet received from a remote OpenVPN peer.  It receives the necessary
 * security parameters in the \a opt argument, which should have been set
 * to the correct values by the \c tls_pre_decrypt() function.
 *
 * This function calls the \c EVP_Cipher* and \c HMAC_* functions of the
 * OpenSSL library to perform the actual security operations.
 *
 * If an error occurs during processing, then the \a buf %buffer is set to
 * empty.
 *
 * @param buf          - The %buffer containing the packet received from a
 *                       remote OpenVPN peer on which to perform security
 *                       operations.
 * @param work         - A working %buffer.
 * @param opt          - The security parameter state for this VPN tunnel.
 * @param frame        - The packet geometry parameters for this VPN
 *                       tunnel.
 *
 * @return
 * @li True, if the packet was authenticated and decrypted successfully.
 * @li False, if an error occurred. \n On return, the \a buf argument will
 *     point to the resulting %buffer.  This %buffer will either contain
 *     the plaintext packet ready for further processing, or be empty if
 *     an error occurred.
 */
bool openvpn_decrypt (struct buffer *buf, struct buffer work,
		      const struct crypto_options *opt,
		      const struct frame* frame);

/** @} name Functions for performing security operations on data channel packets */

void crypto_adjust_frame_parameters(struct frame *frame,
				    const struct key_type* kt,
				    bool cipher_defined,
				    bool use_iv,
				    bool packet_id,
				    bool packet_id_long_form);


/* Minimum length of the nonce used by the PRNG */
#define NONCE_SECRET_LEN_MIN 16

/* Maximum length of the nonce used by the PRNG */
#define NONCE_SECRET_LEN_MAX 64

/** Number of bytes of random to allow before resetting the nonce */
#define PRNG_NONCE_RESET_BYTES 1024

/**
 * Pseudo-random number generator initialisation.
 * (see \c prng_rand_bytes())
 *
 * @param md_name			Name of the message digest to use
 * @param nonce_secret_len_param	Length of the nonce to use
 */
void prng_init (const char *md_name, const int nonce_secret_len_parm);

/*
 * Message digest-based pseudo random number generator.
 *
 * If the PRNG was initialised with a certain message digest, uses the digest
 * to calculate the next random number, and prevent depletion of the entropy
 * pool.
 *
 * This PRNG is aimed at IV generation and similar miscellaneous tasks. Use
 * \c rand_bytes() for higher-assurance functionality.
 *
 * Retrieves len bytes of pseudo random data, and places it in output.
 *
 * @param output	Output buffer
 * @param len		Length of the output buffer
 */
void prng_bytes (uint8_t *output, int len);

void prng_uninit ();

void test_crypto (const struct crypto_options *co, struct frame* f);


/* key direction functions */

void key_direction_state_init (struct key_direction_state *kds, int key_direction);

void verify_fix_key2 (struct key2 *key2, const struct key_type *kt, const char *shared_secret_file);

void must_have_n_keys (const char *filename, const char *option, const struct key2 *key2, int n);

int ascii2keydirection (int msglevel, const char *str);

const char *keydirection2ascii (int kd, bool remote);

/* print keys */
void key2_print (const struct key2* k,
		 const struct key_type *kt,
		 const char* prefix0,
		 const char* prefix1);

#define GHK_INLINE  (1<<0)
void get_tls_handshake_key (const struct key_type *key_type,
			    struct key_ctx_bi *ctx,
			    const char *passphrase_file,
			    const int key_direction,
			    const unsigned int flags);

/*
 * Inline functions
 */

static inline bool
key_ctx_bi_defined(const struct key_ctx_bi* key)
{
  return key->encrypt.cipher || key->encrypt.hmac || key->decrypt.cipher || key->decrypt.hmac;
}


#endif /* ENABLE_CRYPTO */
#endif /* CRYPTO_H */