3 * Protocol definition for TrIPE
5 * (c) 2003 Straylight/Edgeware
8 /*----- Licensing notice --------------------------------------------------*
10 * This file is part of Trivial IP Encryption (TrIPE).
12 * TrIPE is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU General Public License as published by
14 * the Free Software Foundation; either version 2 of the License, or
15 * (at your option) any later version.
17 * TrIPE is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU General Public License for more details.
22 * You should have received a copy of the GNU General Public License
23 * along with TrIPE; if not, write to the Free Software Foundation,
24 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
27 #ifndef TRIPE_PROTOCOL_H
28 #define TRIPE_PROTOCOL_H
30 /*----- TrIPE protocol ----------------------------------------------------*/
32 #define TRIPE_PORT 4070 /* Assigned by IANA */
34 /* --- TrIPE message format --- *
36 * A packet begins with a single-byte message type. The top four bits are a
37 * category code used to send the message to the right general place in the
38 * code; the bottom bits identify the actual message type.
41 #define MSG_CATMASK 0xf0
42 #define MSG_TYPEMASK 0x0f
44 /* --- Encrypted message packets --- *
46 * Messages of category @MSG_PACKET@ contain encrypted network packets. The
47 * message content is a symmetric-encrypted block (see below). Reception of
48 * a packet encrypted under a new key implicitly permits that key to be used
49 * to send further packets.
51 * The only packet type accepted is zero.
53 * Packets may be encrypted under any live keyset, but should use the most
57 #define MSG_PACKET 0x00
59 /* --- Key exchange packets --- */
61 #define MSG_KEYEXCH 0x10
67 #define KX_SWITCHOK 4u
70 /* --- Miscellaneous packets --- */
74 #define MISC_NOP 0u /* Do nothing; ignore me */
75 #define MISC_PING 1u /* Transport-level ping */
76 #define MISC_PONG 2u /* Transport-level ping response */
77 #define MISC_EPING 3u /* Encrypted ping */
78 #define MISC_EPONG 4u /* Encrypted ping response */
79 #define MISC_GREET 5u /* A greeting from a NATed peer */
81 /* --- Symmetric encryption and keysets --- *
83 * Packets consist of an 80-bit MAC, a 32-bit sequence number, and the
86 * The plaintext is encrypted using Blowfish in CBC mode with ciphertext
87 * stealing (as described in [Schneier]). The initialization vector is
88 * selected randomly, and prepended to the actual ciphertext.
90 * The MAC is computed using the HMAC construction with RIPEMD160 over the
91 * sequence number and the ciphertext (with IV); the first 80 bits of the
92 * output are used. (This is the minimum allowed by the draft FIPS for HMAC,
93 * and the recommended truncation.)
95 * A keyset consists of
97 * * an integrity (MAC) key;
98 * * a confidentiality (encryption) key; and
99 * * a sequence numbering space
101 * in each direction. The packets sent by a host encrypted under a
102 * particular keyset are assigned consecutive sequence numbers starting from
103 * zero. The receiving host must ensure that it only accepts each packet at
104 * most once. It should maintain a window of sequence numbers: packets with
105 * numbers beyond the end of the window are accepted and cause the window to
106 * be advanced; packets with numbers before the start of the window are
107 * rejected; packets with numbers which appear within the window are accepted
108 * only if the number has not been seen before.
110 * When a host sends a @KX_SWITCH@ or @KX_SWITCHOK@ message, it installs the
111 * newly-negotiated keyset in a `listen-only' state: it may not send a packet
112 * encrypted under the keyset until either it has received a @KX_SWITCH@ or
113 * @KX_SWITCHOK@ message, or a @MSG_PACKET@ encrypted under the keyset, from
117 /*----- That's all, folks -------------------------------------------------*/