/*
* 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"
/*
* 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 */