1 files changed, 71 insertions, 1 deletions
diff --git a/src/openvpn/crypto.h b/src/openvpn/crypto.h
index bf2f802..e489827 100644
--- a/src/openvpn/crypto.h
+++ b/src/openvpn/crypto.h
@@ -6,7 +6,7 @@
  *             packet compression.
  *
  *  Copyright (C) 2002-2010 OpenVPN Technologies, Inc. <sales@openvpn.net>
- *  Copyright (C) 2010 Fox Crypto B.V. <openvpn@fox-it.com>
+ *  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
@@ -25,6 +25,76 @@
 
 /**
  * @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