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165db1a8 | 1 | /* -*-c-*- |
2 | * | |
0ba8de86 | 3 | * $Id$ |
165db1a8 | 4 | * |
5 | * Protocol definition for TrIPE | |
6 | * | |
7 | * (c) 2003 Straylight/Edgeware | |
8 | */ | |
9 | ||
10 | /*----- Licensing notice --------------------------------------------------* | |
11 | * | |
12 | * This file is part of Trivial IP Encryption (TrIPE). | |
13 | * | |
14 | * TrIPE is free software; you can redistribute it and/or modify | |
15 | * it under the terms of the GNU General Public License as published by | |
16 | * the Free Software Foundation; either version 2 of the License, or | |
17 | * (at your option) any later version. | |
18 | * | |
19 | * TrIPE is distributed in the hope that it will be useful, | |
20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
22 | * GNU General Public License for more details. | |
23 | * | |
24 | * You should have received a copy of the GNU General Public License | |
25 | * along with TrIPE; if not, write to the Free Software Foundation, | |
26 | * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | |
27 | */ | |
28 | ||
165db1a8 | 29 | #ifndef TRIPE_PROTOCOL_H |
30 | #define TRIPE_PROTOCOL_H | |
31 | ||
32 | /*----- TrIPE protocol ----------------------------------------------------*/ | |
33 | ||
34 | /* --- TrIPE message format --- * | |
35 | * | |
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. | |
39 | */ | |
40 | ||
41 | #define MSG_CATMASK 0xf0 | |
42 | #define MSG_TYPEMASK 0x0f | |
43 | ||
44 | /* --- Encrypted message packets --- * | |
45 | * | |
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. | |
50 | * | |
51 | * The only packet type accepted is zero. | |
52 | * | |
53 | * Packets may be encrypted under any live keyset, but should use the most | |
54 | * recent one. | |
55 | */ | |
56 | ||
57 | #define MSG_PACKET 0x00 | |
58 | ||
59 | /* --- Key exchange packets --- */ | |
60 | ||
61 | #define MSG_KEYEXCH 0x10 | |
62 | ||
63 | #define KX_PRECHAL 0u | |
de7bd20b MW |
64 | #define KX_CHAL 1u |
65 | #define KX_REPLY 2u | |
66 | #define KX_SWITCH 3u | |
67 | #define KX_SWITCHOK 4u | |
68 | #define KX_NMSG 5u | |
165db1a8 | 69 | |
0ba8de86 | 70 | /* --- Miscellaneous packets --- */ |
71 | ||
72 | #define MSG_MISC 0x20 | |
73 | ||
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 */ | |
37941236 | 79 | #define MISC_GREET 5u /* A greeting from a NATed peer */ |
0ba8de86 | 80 | |
165db1a8 | 81 | /* --- Symmetric encryption and keysets --- * |
82 | * | |
83 | * Packets consist of an 80-bit MAC, a 32-bit sequence number, and the | |
84 | * encrypted payload. | |
85 | * | |
86 | * The plaintext is encrypted using Blowfish in CBC mode with ciphertext | |
0ba8de86 | 87 | * stealing (as described in [Schneier]). The initialization vector is |
165db1a8 | 88 | * selected randomly, and prepended to the actual ciphertext. |
89 | * | |
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.) | |
94 | * | |
95 | * A keyset consists of | |
96 | * | |
97 | * * an integrity (MAC) key; | |
98 | * * a confidentiality (encryption) key; and | |
99 | * * a sequence numbering space | |
100 | * | |
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. | |
109 | * | |
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 | |
114 | * its peer. | |
115 | */ | |
116 | ||
117 | /*----- That's all, folks -------------------------------------------------*/ | |
118 | ||
119 | #endif |