首先需要实现MD5，网上发现一个较好的实现：
1、md5.h
1 #ifndef _MD5_H_
2 #define _MD5_H_
3 /*
4 * This is an OpenSSL-compatible implementation of the RSA Data Security, Inc.
5 * MD5 Message-Digest Algorithm (RFC 1321).
6 *
7 * Homepage:
8 * http://openwall.info/wiki/people/solar/software/public-domain-source-code/md5
9 *
10 * Author:
11 * Alexander Peslyak, better known as Solar Designer <solar at openwall.com>
12 *
13 * This software was written by Alexander Peslyak in 2001. No copyright is
14 * claimed, and the software is hereby placed in the public domain.
15 * In case this attempt to disclaim copyright and place the software in the
16 * public domain is deemed null and void, then the software is
17 * Copyright (c) 2001 Alexander Peslyak and it is hereby released to the
18 * general public under the following terms:
19 *
20 * Redistribution and use in source and binary forms, with or without
21 * modification, are permitted.
22 *
23 * There‘s ABSOLUTELY NO WARRANTY, express or implied.
24 *
25 * See md5.c for more information.
26 */
27
28
29 /* Any 32-bit or wider unsigned integer data type will do */
30 typedef unsigned int MD5_u32plus;
31
32 typedef struct {
33 MD5_u32plus lo, hi;
34 MD5_u32plus a, b, c, d;
35 unsigned char buffer[64];
36 MD5_u32plus block[16];
37 } MD5_CTX;
38
39 extern void MD5_Init(MD5_CTX *ctx);
40 extern void MD5_Update(MD5_CTX *ctx, const void *data, unsigned long size);
41 extern void MD5_Final(unsigned char *result, MD5_CTX *ctx);
42
43
44 #endif // _MD5_H_
2、md5.c
1 /*
2 * This is an OpenSSL-compatible implementation of the RSA Data Security, Inc.
3 * MD5 Message-Digest Algorithm (RFC 1321).
4 *
5 * Homepage:
6 * http://openwall.info/wiki/people/solar/software/public-domain-source-code/md5
7 *
8 * Author:
9 * Alexander Peslyak, better known as Solar Designer <solar at openwall.com>
10 *
11 * This software was written by Alexander Peslyak in 2001. No copyright is
12 * claimed, and the software is hereby placed in the public domain.
13 * In case this attempt to disclaim copyright and place the software in the
14 * public domain is deemed null and void, then the software is
15 * Copyright (c) 2001 Alexander Peslyak and it is hereby released to the
16 * general public under the following terms:
17 *
18 * Redistribution and use in source and binary forms, with or without
19 * modification, are permitted.
20 *
21 * There‘s ABSOLUTELY NO WARRANTY, express or implied.
22 *
23 * (This is a heavily cut-down "BSD license".)
24 *
25 * This differs from Colin Plumb‘s older public domain implementation in that
26 * no exactly 32-bit integer data type is required (any 32-bit or wider
27 * unsigned integer data type will do), there‘s no compile-time endianness
28 * configuration, and the function prototypes match OpenSSL‘s. No code from
29 * Colin Plumb‘s implementation has been reused; this comment merely compares
30 * the properties of the two independent implementations.
31 *
32 * The primary goals of this implementation are portability and ease of use.
33 * It is meant to be fast, but not as fast as possible. Some known
34 * optimizations are not included to reduce source code size and avoid
35 * compile-time configuration.
36 */
37
38 #include <string.h>
39
40 #include "md5.h"
41
42 /*
43 * The basic MD5 functions.
44 *
45 * F and G are optimized compared to their RFC 1321 definitions for
46 * architectures that lack an AND-NOT instruction, just like in Colin Plumb‘s
47 * implementation.
48 */
49 #define F(x, y, z) ((z) ^ ((x) & ((y) ^ (z))))
50 #define G(x, y, z) ((y) ^ ((z) & ((x) ^ (y))))
51 #define H(x, y, z) (((x) ^ (y)) ^ (z))
52 #define H2(x, y, z) ((x) ^ ((y) ^ (z)))
53 #define I(x, y, z) ((y) ^ ((x) | ~(z)))
54
55 /*
56 * The MD5 transformation for all four rounds.
57 */
58 #define STEP(f, a, b, c, d, x, t, s) 59 (a) += f((b), (c), (d)) + (x) + (t); 60 (a) = (((a) << (s)) | (((a) & 0xffffffff) >> (32 - (s)))); 61 (a) += (b);
62
63 /*
64 * SET reads 4 input bytes in little-endian byte order and stores them
65 * in a properly aligned word in host byte order.
66 *
67 * The check for little-endian architectures that tolerate unaligned
68 * memory accesses is just an optimization. Nothing will break if it
69 * doesn‘t work.
70 */
71 #if defined(__i386__) || defined(__x86_64__) || defined(__vax__)
72 #define SET(n) 73 (*(MD5_u32plus *)&ptr[(n) * 4])
74 #define GET(n) 75 SET(n)
76 #else
77 #define SET(n) 78 (ctx->block[(n)] = 79 (MD5_u32plus)ptr[(n) * 4] | 80 ((MD5_u32plus)ptr[(n) * 4 + 1] << 8) | 81 ((MD5_u32plus)ptr[(n) * 4 + 2] << 16) | 82 ((MD5_u32plus)ptr[(n) * 4 + 3] << 24))
83 #define GET(n) 84 (ctx->block[(n)])
85 #endif
86
87 /*
88 * This processes one or more 64-byte data blocks, but does NOT update
89 * the bit counters. There are no alignment requirements.
90 */
91 static const void *body(MD5_CTX *ctx, const void *data, unsigned long size)
92 {
93 const unsigned char *ptr;
94 MD5_u32plus a, b, c, d;
95 MD5_u32plus saved_a, saved_b, saved_c, saved_d;
96
97 ptr = (const unsigned char *)data;
98
99 a = ctx->a;
100 b = ctx->b;
101 c = ctx->c;
102 d = ctx->d;
103
104 do {
105 saved_a = a;
106 saved_b = b;
107 saved_c = c;
108 saved_d = d;
109
110 /* Round 1 */
111 STEP(F, a, b, c, d, SET(0), 0xd76aa478, 7)
112 STEP(F, d, a, b, c, SET(1), 0xe8c7b756, 12)
113 STEP(F, c, d, a, b, SET(2), 0x242070db, 17)
114 STEP(F, b, c, d, a, SET(3), 0xc1bdceee, 22)
115 STEP(F, a, b, c, d, SET(4), 0xf57c0faf, 7)
116 STEP(F, d, a, b, c, SET(5), 0x4787c62a, 12)
117 STEP(F, c, d, a, b, SET(6), 0xa8304613, 17)
118 STEP(F, b, c, d, a, SET(7), 0xfd469501, 22)
119 STEP(F, a, b, c, d, SET(8), 0x698098d8, 7)
120 STEP(F, d, a, b, c, SET(9), 0x8b44f7af, 12)
121 STEP(F, c, d, a, b, SET(10), 0xffff5bb1, 17)
122 STEP(F, b, c, d, a, SET(11), 0x895cd7be, 22)
123 STEP(F, a, b, c, d, SET(12), 0x6b901122, 7)
124 STEP(F, d, a, b, c, SET(13), 0xfd987193, 12)
125 STEP(F, c, d, a, b, SET(14), 0xa679438e, 17)
126 STEP(F, b, c, d, a, SET(15), 0x49b40821, 22)
127
128 /* Round 2 */
129 STEP(G, a, b, c, d, GET(1), 0xf61e2562, 5)
130 STEP(G, d, a, b, c, GET(6), 0xc040b340, 9)
131 STEP(G, c, d, a, b, GET(11), 0x265e5a51, 14)
132 STEP(G, b, c, d, a, GET(0), 0xe9b6c7aa, 20)
133 STEP(G, a, b, c, d, GET(5), 0xd62f105d, 5)
134 STEP(G, d, a, b, c, GET(10), 0x02441453, 9)
135 STEP(G, c, d, a, b, GET(15), 0xd8a1e681, 14)
136 STEP(G, b, c, d, a, GET(4), 0xe7d3fbc8, 20)
137 STEP(G, a, b, c, d, GET(9), 0x21e1cde6, 5)
138 STEP(G, d, a, b, c, GET(14), 0xc33707d6, 9)
139 STEP(G, c, d, a, b, GET(3), 0xf4d50d87, 14)
140 STEP(G, b, c, d, a, GET(8), 0x455a14ed, 20)
141 STEP(G, a, b, c, d, GET(13), 0xa9e3e905, 5)
142 STEP(G, d, a, b, c, GET(2), 0xfcefa3f8, 9)
143 STEP(G, c, d, a, b, GET(7), 0x676f02d9, 14)
144 STEP(G, b, c, d, a, GET(12), 0x8d2a4c8a, 20)
145
146 /* Round 3 */
147 STEP(H, a, b, c, d, GET(5), 0xfffa3942, 4)
148 STEP(H2, d, a, b, c, GET(8), 0x8771f681, 11)
149 STEP(H, c, d, a, b, GET(11), 0x6d9d6122, 16)
150 STEP(H2, b, c, d, a, GET(14), 0xfde5380c, 23)
151 STEP(H, a, b, c, d, GET(1), 0xa4beea44, 4)
152 STEP(H2, d, a, b, c, GET(4), 0x4bdecfa9, 11)
153 STEP(H, c, d, a, b, GET(7), 0xf6bb4b60, 16)
154 STEP(H2, b, c, d, a, GET(10), 0xbebfbc70, 23)
155 STEP(H, a, b, c, d, GET(13), 0x289b7ec6, 4)
156 STEP(H2, d, a, b, c, GET(0), 0xeaa127fa, 11)
157 STEP(H, c, d, a, b, GET(3), 0xd4ef3085, 16)
158 STEP(H2, b, c, d, a, GET(6), 0x04881d05, 23)
159 STEP(H, a, b, c, d, GET(9), 0xd9d4d039, 4)
160 STEP(H2, d, a, b, c, GET(12), 0xe6db99e5, 11)
161 STEP(H, c, d, a, b, GET(15), 0x1fa27cf8, 16)
162 STEP(H2, b, c, d, a, GET(2), 0xc4ac5665, 23)
163
164 /* Round 4 */
165 STEP(I, a, b, c, d, GET(0), 0xf4292244, 6)
166 STEP(I, d, a, b, c, GET(7), 0x432aff97, 10)
167 STEP(I, c, d, a, b, GET(14), 0xab9423a7, 15)
168 STEP(I, b, c, d, a, GET(5), 0xfc93a039, 21)
169 STEP(I, a, b, c, d, GET(12), 0x655b59c3, 6)
170 STEP(I, d, a, b, c, GET(3), 0x8f0ccc92, 10)
171 STEP(I, c, d, a, b, GET(10), 0xffeff47d, 15)
172 STEP(I, b, c, d, a, GET(1), 0x85845dd1, 21)
173 STEP(I, a, b, c, d, GET(8), 0x6fa87e4f, 6)
174 STEP(I, d, a, b, c, GET(15), 0xfe2ce6e0, 10)
175 STEP(I, c, d, a, b, GET(6), 0xa3014314, 15)
176 STEP(I, b, c, d, a, GET(13), 0x4e0811a1, 21)
177 STEP(I, a, b, c, d, GET(4), 0xf7537e82, 6)
178 STEP(I, d, a, b, c, GET(11), 0xbd3af235, 10)
179 STEP(I, c, d, a, b, GET(2), 0x2ad7d2bb, 15)
180 STEP(I, b, c, d, a, GET(9), 0xeb86d391, 21)
181
182 a += saved_a;
183 b += saved_b;
184 c += saved_c;
185 d += saved_d;
186
187 ptr += 64;
188 } while (size -= 64);
189
190 ctx->a = a;
191 ctx->b = b;
192 ctx->c = c;
193 ctx->d = d;
194
195 return ptr;
196 }
197
198 void MD5_Init(MD5_CTX *ctx)
199 {
200 ctx->a = 0x67452301;
201 ctx->b = 0xefcdab89;
202 ctx->c = 0x98badcfe;
203 ctx->d = 0x10325476;
204
205 ctx->lo = 0;
206 ctx->hi = 0;
207 }
208
209 void MD5_Update(MD5_CTX *ctx, const void *data, unsigned long size)
210 {
211 MD5_u32plus saved_lo;
212 unsigned long used, available;
213
214 saved_lo = ctx->lo;
215 if ((ctx->lo = (saved_lo + size) & 0x1fffffff) < saved_lo)
216 ctx->hi++;
217 ctx->hi += size >> 29;
218
219 used = saved_lo & 0x3f;
220
221 if (used) {
222 available = 64 - used;
223
224 if (size < available) {
225 memcpy(&ctx->buffer[used], data, size);
226 return;
227 }
228
229 memcpy(&ctx->buffer[used], data, available);
230 data = (const unsigned char *)data + available;
231 size -= available;
232 body(ctx, ctx->buffer, 64);
233 }
234
235 if (size >= 64) {
236 data = body(ctx, data, size & ~(unsigned long)0x3f);
237 size &= 0x3f;
238 }
239
240 memcpy(ctx->buffer, data, size);
241 }
242
243 void MD5_Final(unsigned char *result, MD5_CTX *ctx)
244 {
245 unsigned long used, available;
246
247 used = ctx->lo & 0x3f;
248
249 ctx->buffer[used++] = 0x80;
250
251 available = 64 - used;
252
253 if (available < 8) {
254 memset(&ctx->buffer[used], 0, available);
255 body(ctx, ctx->buffer, 64);
256 used = 0;
257 available = 64;
258 }
259
260 memset(&ctx->buffer[used], 0, available - 8);
261
262 ctx->lo <<= 3;
263 ctx->buffer[56] = ctx->lo;
264 ctx->buffer[57] = ctx->lo >> 8;
265 ctx->buffer[58] = ctx->lo >> 16;
266 ctx->buffer[59] = ctx->lo >> 24;
267 ctx->buffer[60] = ctx->hi;
268 ctx->buffer[61] = ctx->hi >> 8;
269 ctx->buffer[62] = ctx->hi >> 16;
270 ctx->buffer[63] = ctx->hi >> 24;
271
272 body(ctx, ctx->buffer, 64);
273
274 result[0] = ctx->a;
275 result[1] = ctx->a >> 8;
276 result[2] = ctx->a >> 16;
277 result[3] = ctx->a >> 24;
278 result[4] = ctx->b;
279 result[5] = ctx->b >> 8;
280 result[6] = ctx->b >> 16;
281 result[7] = ctx->b >> 24;
282 result[8] = ctx->c;
283 result[9] = ctx->c >> 8;
284 result[10] = ctx->c >> 16;
285 result[11] = ctx->c >> 24;
286 result[12] = ctx->d;
287 result[13] = ctx->d >> 8;
288 result[14] = ctx->d >> 16;
289 result[15] = ctx->d >> 24;
290
291 memset(ctx, 0, sizeof(*ctx));
292 }
3、简单测试
1 #include <stdio.h>
2 #include <string.h>
3 #include <stdlib.h>
4 #include "md5.h"
5
6 // enter start position and end position
7 unsigned char* getMD5InRange(const char* filename, long startpos, long endpos)
8 {
9 FILE* file = fopen(filename, "r");
10 fseek(file, startpos, SEEK_SET); // redirect the file pointer to start position
11 char *buf = (char *)malloc(endpos-startpos+1);
12 fread(buf, sizeof(char), endpos-startpos+1, file); // read the data to buffer
13
14 printf("buf: %s\n", buf);
15 unsigned char *decrypt = (unsigned char *)malloc(sizeof(unsigned char*)*16);
16 MD5_CTX md5;
17 MD5_Init(&md5); // three steps to get md5
18 MD5_Update(&md5, buf, strlen(buf));
19 MD5_Final(decrypt, &md5);
20 fclose(file);
21 return decrypt;
22 }
23
24
25 int main(int argc, char* argv[])
26 {
27 int i, st, ed;
28 unsigned char *decrypt2;
29
30 while(~scanf("%d%d", &st, &ed))
31 {
32 decrypt2 = getMD5InRange("aaa.txt", st, ed);
33 for(i = 0; i < 16; i++)
34 printf("%02x", decrypt2[i]);
35 printf("\n");
36 }
37 return 0;
38 }
4、文本文件aaa.txt
shanghaisndacompanygrandcloudwww.grandcloud.com
5、Makefile
test: test.o md5.o
cc -o test test.o md5.o
test.o : test.c md5.h
cc -c test.c md5.c
6、运行结果（centos6.6，请在unix环境下编译运行）
时间： 2024-08-05 15:00:14