1 /*
2 * Copyright (c) 1998-2006 The TCPDUMP project
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that: (1) source code
6 * distributions retain the above copyright notice and this paragraph
7 * in its entirety, and (2) distributions including binary code include
8 * the above copyright notice and this paragraph in its entirety in
9 * the documentation or other materials provided with the distribution.
10 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND
11 * WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT
12 * LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
13 * FOR A PARTICULAR PURPOSE.
14 *
15 * miscellaneous checksumming routines
16 *
17 * Original code by Hannes Gredler (hannes@gredler.at)
18 */
19
20 #include <config.h>
21
22 #include "netdissect-stdinc.h"
23
24 #include <stdio.h>
25 #include <stdlib.h>
26 #include <string.h>
27
28 #include "netdissect.h"
29
30 /*
31 * CRC-10 table generated using the following Python snippet:
32
33 import sys
34
35 crc_table = []
36 for i in range(256):
37 accum = i << 2
38 for j in range(8):
39 accum <<= 1
40 if accum & 0x400:
41 accum ^= 0x633
42 crc_table.append(accum)
43
44 for i in range(int(len(crc_table)/8)):
45 for j in range(8):
46 sys.stdout.write("0x%04x, " % crc_table[i*8+j])
47 sys.stdout.write("\n")
48
49 */
50 static const uint16_t crc10_table[256] =
51 {
52 0x0000, 0x0233, 0x0255, 0x0066, 0x0299, 0x00aa, 0x00cc, 0x02ff,
53 0x0301, 0x0132, 0x0154, 0x0367, 0x0198, 0x03ab, 0x03cd, 0x01fe,
54 0x0031, 0x0202, 0x0264, 0x0057, 0x02a8, 0x009b, 0x00fd, 0x02ce,
55 0x0330, 0x0103, 0x0165, 0x0356, 0x01a9, 0x039a, 0x03fc, 0x01cf,
56 0x0062, 0x0251, 0x0237, 0x0004, 0x02fb, 0x00c8, 0x00ae, 0x029d,
57 0x0363, 0x0150, 0x0136, 0x0305, 0x01fa, 0x03c9, 0x03af, 0x019c,
58 0x0053, 0x0260, 0x0206, 0x0035, 0x02ca, 0x00f9, 0x009f, 0x02ac,
59 0x0352, 0x0161, 0x0107, 0x0334, 0x01cb, 0x03f8, 0x039e, 0x01ad,
60 0x00c4, 0x02f7, 0x0291, 0x00a2, 0x025d, 0x006e, 0x0008, 0x023b,
61 0x03c5, 0x01f6, 0x0190, 0x03a3, 0x015c, 0x036f, 0x0309, 0x013a,
62 0x00f5, 0x02c6, 0x02a0, 0x0093, 0x026c, 0x005f, 0x0039, 0x020a,
63 0x03f4, 0x01c7, 0x01a1, 0x0392, 0x016d, 0x035e, 0x0338, 0x010b,
64 0x00a6, 0x0295, 0x02f3, 0x00c0, 0x023f, 0x000c, 0x006a, 0x0259,
65 0x03a7, 0x0194, 0x01f2, 0x03c1, 0x013e, 0x030d, 0x036b, 0x0158,
66 0x0097, 0x02a4, 0x02c2, 0x00f1, 0x020e, 0x003d, 0x005b, 0x0268,
67 0x0396, 0x01a5, 0x01c3, 0x03f0, 0x010f, 0x033c, 0x035a, 0x0169,
68 0x0188, 0x03bb, 0x03dd, 0x01ee, 0x0311, 0x0122, 0x0144, 0x0377,
69 0x0289, 0x00ba, 0x00dc, 0x02ef, 0x0010, 0x0223, 0x0245, 0x0076,
70 0x01b9, 0x038a, 0x03ec, 0x01df, 0x0320, 0x0113, 0x0175, 0x0346,
71 0x02b8, 0x008b, 0x00ed, 0x02de, 0x0021, 0x0212, 0x0274, 0x0047,
72 0x01ea, 0x03d9, 0x03bf, 0x018c, 0x0373, 0x0140, 0x0126, 0x0315,
73 0x02eb, 0x00d8, 0x00be, 0x028d, 0x0072, 0x0241, 0x0227, 0x0014,
74 0x01db, 0x03e8, 0x038e, 0x01bd, 0x0342, 0x0171, 0x0117, 0x0324,
75 0x02da, 0x00e9, 0x008f, 0x02bc, 0x0043, 0x0270, 0x0216, 0x0025,
76 0x014c, 0x037f, 0x0319, 0x012a, 0x03d5, 0x01e6, 0x0180, 0x03b3,
77 0x024d, 0x007e, 0x0018, 0x022b, 0x00d4, 0x02e7, 0x0281, 0x00b2,
78 0x017d, 0x034e, 0x0328, 0x011b, 0x03e4, 0x01d7, 0x01b1, 0x0382,
79 0x027c, 0x004f, 0x0029, 0x021a, 0x00e5, 0x02d6, 0x02b0, 0x0083,
80 0x012e, 0x031d, 0x037b, 0x0148, 0x03b7, 0x0184, 0x01e2, 0x03d1,
81 0x022f, 0x001c, 0x007a, 0x0249, 0x00b6, 0x0285, 0x02e3, 0x00d0,
82 0x011f, 0x032c, 0x034a, 0x0179, 0x0386, 0x01b5, 0x01d3, 0x03e0,
83 0x021e, 0x002d, 0x004b, 0x0278, 0x0087, 0x02b4, 0x02d2, 0x00e1
84 };
85
86 uint16_t
verify_crc10_cksum(uint16_t accum,const u_char * p,int length)87 verify_crc10_cksum(uint16_t accum, const u_char *p, int length)
88 {
89 int i;
90
91 for ( i = 0; i < length; i++ ) {
92 accum = ((accum << 8) & 0x3ff)
93 ^ crc10_table[( accum >> 2) & 0xff]
94 ^ *p++;
95 }
96 return accum;
97 }
98
99 /*
100 * Creates the OSI Fletcher checksum. See 8473-1, Appendix C, section C.3.
101 * The checksum field of the passed PDU does not need to be reset to zero.
102 */
103 uint16_t
create_osi_cksum(const uint8_t * pptr,int checksum_offset,int length)104 create_osi_cksum (const uint8_t *pptr, int checksum_offset, int length)
105 {
106
107 int x;
108 int y;
109 uint32_t mul;
110 uint32_t c0;
111 uint32_t c1;
112 uint16_t checksum;
113 int idx;
114
115 c0 = 0;
116 c1 = 0;
117
118 for (idx = 0; idx < length; idx++) {
119 /*
120 * Ignore the contents of the checksum field.
121 */
122 if (idx == checksum_offset ||
123 idx == checksum_offset+1) {
124 c1 += c0;
125 pptr++;
126 } else {
127 c0 = c0 + *(pptr++);
128 c1 += c0;
129 }
130 }
131
132 c0 = c0 % 255;
133 c1 = c1 % 255;
134
135 mul = (length - checksum_offset)*(c0);
136
137 x = mul - c0 - c1;
138 y = c1 - mul - 1;
139
140 if ( y >= 0 ) y++;
141 if ( x < 0 ) x--;
142
143 x %= 255;
144 y %= 255;
145
146
147 if (x == 0) x = 255;
148 if (y == 0) y = 255;
149
150 y &= 0x00FF;
151 checksum = ((x << 8) | y);
152
153 return checksum;
154 }
155