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1 office 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@juniper.net)
18 */
19  
20 #define NETDISSECT_REWORKED
21 #ifdef HAVE_CONFIG_H
22 #include "config.h"
23 #endif
24  
25 #include <tcpdump-stdinc.h>
26  
27 #include <stdio.h>
28 #include <stdlib.h>
29 #include <string.h>
30 #include <assert.h>
31  
32 #include "interface.h"
33  
34 /*
35 * CRC-10 table generated using the following Python snippet:
36  
37 import sys
38  
39 crc_table = []
40 for i in range(256):
41 accum = i << 2
42 for j in range(8):
43 accum <<= 1
44 if accum & 0x400:
45 accum ^= 0x633
46 crc_table.append(accum)
47  
48 for i in range(len(crc_table)/8):
49 for j in range(8):
50 sys.stdout.write("0x%04x, " % crc_table[i*8+j])
51 sys.stdout.write("\n")
52  
53 */
54 static const uint16_t crc10_table[256] =
55 {
56 0x0000, 0x0233, 0x0255, 0x0066, 0x0299, 0x00aa, 0x00cc, 0x02ff,
57 0x0301, 0x0132, 0x0154, 0x0367, 0x0198, 0x03ab, 0x03cd, 0x01fe,
58 0x0031, 0x0202, 0x0264, 0x0057, 0x02a8, 0x009b, 0x00fd, 0x02ce,
59 0x0330, 0x0103, 0x0165, 0x0356, 0x01a9, 0x039a, 0x03fc, 0x01cf,
60 0x0062, 0x0251, 0x0237, 0x0004, 0x02fb, 0x00c8, 0x00ae, 0x029d,
61 0x0363, 0x0150, 0x0136, 0x0305, 0x01fa, 0x03c9, 0x03af, 0x019c,
62 0x0053, 0x0260, 0x0206, 0x0035, 0x02ca, 0x00f9, 0x009f, 0x02ac,
63 0x0352, 0x0161, 0x0107, 0x0334, 0x01cb, 0x03f8, 0x039e, 0x01ad,
64 0x00c4, 0x02f7, 0x0291, 0x00a2, 0x025d, 0x006e, 0x0008, 0x023b,
65 0x03c5, 0x01f6, 0x0190, 0x03a3, 0x015c, 0x036f, 0x0309, 0x013a,
66 0x00f5, 0x02c6, 0x02a0, 0x0093, 0x026c, 0x005f, 0x0039, 0x020a,
67 0x03f4, 0x01c7, 0x01a1, 0x0392, 0x016d, 0x035e, 0x0338, 0x010b,
68 0x00a6, 0x0295, 0x02f3, 0x00c0, 0x023f, 0x000c, 0x006a, 0x0259,
69 0x03a7, 0x0194, 0x01f2, 0x03c1, 0x013e, 0x030d, 0x036b, 0x0158,
70 0x0097, 0x02a4, 0x02c2, 0x00f1, 0x020e, 0x003d, 0x005b, 0x0268,
71 0x0396, 0x01a5, 0x01c3, 0x03f0, 0x010f, 0x033c, 0x035a, 0x0169,
72 0x0188, 0x03bb, 0x03dd, 0x01ee, 0x0311, 0x0122, 0x0144, 0x0377,
73 0x0289, 0x00ba, 0x00dc, 0x02ef, 0x0010, 0x0223, 0x0245, 0x0076,
74 0x01b9, 0x038a, 0x03ec, 0x01df, 0x0320, 0x0113, 0x0175, 0x0346,
75 0x02b8, 0x008b, 0x00ed, 0x02de, 0x0021, 0x0212, 0x0274, 0x0047,
76 0x01ea, 0x03d9, 0x03bf, 0x018c, 0x0373, 0x0140, 0x0126, 0x0315,
77 0x02eb, 0x00d8, 0x00be, 0x028d, 0x0072, 0x0241, 0x0227, 0x0014,
78 0x01db, 0x03e8, 0x038e, 0x01bd, 0x0342, 0x0171, 0x0117, 0x0324,
79 0x02da, 0x00e9, 0x008f, 0x02bc, 0x0043, 0x0270, 0x0216, 0x0025,
80 0x014c, 0x037f, 0x0319, 0x012a, 0x03d5, 0x01e6, 0x0180, 0x03b3,
81 0x024d, 0x007e, 0x0018, 0x022b, 0x00d4, 0x02e7, 0x0281, 0x00b2,
82 0x017d, 0x034e, 0x0328, 0x011b, 0x03e4, 0x01d7, 0x01b1, 0x0382,
83 0x027c, 0x004f, 0x0029, 0x021a, 0x00e5, 0x02d6, 0x02b0, 0x0083,
84 0x012e, 0x031d, 0x037b, 0x0148, 0x03b7, 0x0184, 0x01e2, 0x03d1,
85 0x022f, 0x001c, 0x007a, 0x0249, 0x00b6, 0x0285, 0x02e3, 0x00d0,
86 0x011f, 0x032c, 0x034a, 0x0179, 0x0386, 0x01b5, 0x01d3, 0x03e0,
87 0x021e, 0x002d, 0x004b, 0x0278, 0x0087, 0x02b4, 0x02d2, 0x00e1
88 };
89  
90 static void
91 init_crc10_table(void)
92 {
93 #define CRC10_POLYNOMIAL 0x633
94 register int i, j;
95 register uint16_t accum;
96 uint16_t verify_crc10_table[256];
97  
98 for ( i = 0; i < 256; i++ )
99 {
100 accum = ((unsigned short) i << 2);
101 for ( j = 0; j < 8; j++ )
102 {
103 if ((accum <<= 1) & 0x400) accum ^= CRC10_POLYNOMIAL;
104 }
105 verify_crc10_table[i] = accum;
106 }
107 assert(memcmp(verify_crc10_table,
108 crc10_table,
109 sizeof(verify_crc10_table)) == 0);
110 #undef CRC10_POLYNOMIAL
111 }
112  
113 uint16_t
114 verify_crc10_cksum(uint16_t accum, const u_char *p, int length)
115 {
116 register int i;
117  
118 for ( i = 0; i < length; i++ )
119 {
120 accum = ((accum << 8) & 0x3ff)
121 ^ crc10_table[( accum >> 2) & 0xff]
122 ^ *p++;
123 }
124 return accum;
125 }
126  
127 /* precompute checksum tables */
128 void
129 init_checksum(void) {
130  
131 init_crc10_table();
132  
133 }
134  
135 /*
136 * Creates the OSI Fletcher checksum. See 8473-1, Appendix C, section C.3.
137 * The checksum field of the passed PDU does not need to be reset to zero.
138 */
139 uint16_t
140 create_osi_cksum (const uint8_t *pptr, int checksum_offset, int length)
141 {
142  
143 int x;
144 int y;
145 uint32_t mul;
146 uint32_t c0;
147 uint32_t c1;
148 uint16_t checksum;
149 int index;
150  
151 c0 = 0;
152 c1 = 0;
153  
154 for (index = 0; index < length; index++) {
155 /*
156 * Ignore the contents of the checksum field.
157 */
158 if (index == checksum_offset ||
159 index == checksum_offset+1) {
160 c1 += c0;
161 pptr++;
162 } else {
163 c0 = c0 + *(pptr++);
164 c1 += c0;
165 }
166 }
167  
168 c0 = c0 % 255;
169 c1 = c1 % 255;
170  
171 mul = (length - checksum_offset)*(c0);
172  
173 x = mul - c0 - c1;
174 y = c1 - mul - 1;
175  
176 if ( y >= 0 ) y++;
177 if ( x < 0 ) x--;
178  
179 x %= 255;
180 y %= 255;
181  
182  
183 if (x == 0) x = 255;
184 if (y == 0) y = 255;
185  
186 y &= 0x00FF;
187 checksum = ((x << 8) | y);
188  
189 return checksum;
190 }