网上找到的实现md5函数代码，包括一个头文件md5.h和一个源文件md5.c，用下面的测试代码test.c测试通过，各文件依次如下：
.h文件——md5.h
#ifndef MD5_H#define MD5_Htypedef struct{unsigned int count[2];unsigned int state[4];unsigned char buffer[64]; }MD5_CTX;#define F(x,y,z) ((x & y) | (~x & z))#define G(x,y,z) ((x & z) | (y & ~z))#define H(x,y,z) (x^y^z)#define I(x,y,z) (y ^ (x | ~z))#define ROTATE_LEFT(x,n) ((x << n) | (x >> (32-n)))#define FF(a,b,c,d,x,s,ac) \{ \a += F(b,c,d) + x + ac; \a = ROTATE_LEFT(a,s); \a += b; \}#define GG(a,b,c,d,x,s,ac) \{ \a += G(b,c,d) + x + ac; \a = ROTATE_LEFT(a,s); \a += b; \}#define HH(a,b,c,d,x,s,ac) \{ \a += H(b,c,d) + x + ac; \a = ROTATE_LEFT(a,s); \a += b; \}#define II(a,b,c,d,x,s,ac) \{ \a += I(b,c,d) + x + ac; \a = ROTATE_LEFT(a,s); \a += b; \} void MD5Init(MD5_CTX *context);void MD5Update(MD5_CTX *context,unsigned char *input,unsigned int inputlen);void MD5Final(MD5_CTX *context,unsigned char digest[16]);void MD5Transform(unsigned int state[4],unsigned char block[64]);void MD5Encode(unsigned char *output,unsigned int *input,unsigned int len);void MD5Decode(unsigned int *output,unsigned char *input,unsigned int len);#endif
.c文件——md5.c
#include <memory.h>#include "md5.h"unsigned char PADDING[]={0x80,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};void MD5Init(MD5_CTX *context){context->count[0] = 0;context->count[1] = 0;context->state[0] = 0x67452301;context->state[1] = 0xEFCDAB89;context->state[2] = 0x98BADCFE;context->state[3] = 0x10325476;}void MD5Update(MD5_CTX *context,unsigned char *input,unsigned int inputlen){unsigned int i = 0,index = 0,partlen = 0;index = (context->count[0] >> 3) & 0x3F;partlen = 64 - index;context->count[0] += inputlen << 3;if(context->count[0] < (inputlen << 3))context->count[1]++;context->count[1] += inputlen >> 29;if(inputlen >= partlen){memcpy(&context->buffer[index],input,partlen);MD5Transform(context->state,context->buffer);for(i = partlen;i+64 <= inputlen;i+=64)MD5Transform(context->state,&input[i]);index = 0; } else{i = 0;}memcpy(&context->buffer[index],&input[i],inputlen-i);}void MD5Final(MD5_CTX *context,unsigned char digest[16]){unsigned int index = 0,padlen = 0;unsigned char bits[8];index = (context->count[0] >> 3) & 0x3F;padlen = (index < 56)?(56-index):(120-index);MD5Encode(bits,context->count,8);MD5Update(context,PADDING,padlen);MD5Update(context,bits,8);MD5Encode(digest,context->state,16);}void MD5Encode(unsigned char *output,unsigned int *input,unsigned int len){unsigned int i = 0,j = 0;while(j < len){output[j] = input[i] & 0xFF; output[j+1] = (input[i] >> 8) & 0xFF;output[j+2] = (input[i] >> 16) & 0xFF;output[j+3] = (input[i] >> 24) & 0xFF;i++;j+=4;}}void MD5Decode(unsigned int *output,unsigned char *input,unsigned int len){unsigned int i = 0,j = 0;while(j < len){output[i] = (input[j]) |(input[j+1] << 8) |(input[j+2] << 16) |(input[j+3] << 24);i++;j+=4; }}void MD5Transform(unsigned int state[4],unsigned char block[64]){unsigned int a = state[0];unsigned int b = state[1];unsigned int c = state[2];unsigned int d = state[3];unsigned int x[64];MD5Decode(x,block,64);FF(a, b, c, d, x[ 0], 7, 0xd76aa478); /* 1 */FF(d, a, b, c, x[ 1], 12, 0xe8c7b756); /* 2 */FF(c, d, a, b, x[ 2], 17, 0x242070db); /* 3 */FF(b, c, d, a, x[ 3], 22, 0xc1bdceee); /* 4 */FF(a, b, c, d, x[ 4], 7, 0xf57c0faf); /* 5 */FF(d, a, b, c, x[ 5], 12, 0x4787c62a); /* 6 */FF(c, d, a, b, x[ 6], 17, 0xa8304613); /* 7 */FF(b, c, d, a, x[ 7], 22, 0xfd469501); /* 8 */FF(a, b, c, d, x[ 8], 7, 0x698098d8); /* 9 */FF(d, a, b, c, x[ 9], 12, 0x8b44f7af); /* 10 */FF(c, d, a, b, x[10], 17, 0xffff5bb1); /* 11 */FF(b, c, d, a, x[11], 22, 0x895cd7be); /* 12 */FF(a, b, c, d, x[12], 7, 0x6b901122); /* 13 */FF(d, a, b, c, x[13], 12, 0xfd987193); /* 14 */FF(c, d, a, b, x[14], 17, 0xa679438e); /* 15 */FF(b, c, d, a, x[15], 22, 0x49b40821); /* 16 *//* Round 2 */GG(a, b, c, d, x[ 1], 5, 0xf61e2562); /* 17 */GG(d, a, b, c, x[ 6], 9, 0xc040b340); /* 18 */GG(c, d, a, b, x[11], 14, 0x265e5a51); /* 19 */GG(b, c, d, a, x[ 0], 20, 0xe9b6c7aa); /* 20 */GG(a, b, c, d, x[ 5], 5, 0xd62f105d); /* 21 */GG(d, a, b, c, x[10], 9, 0x2441453); /* 22 */GG(c, d, a, b, x[15], 14, 0xd8a1e681); /* 23 */GG(b, c, d, a, x[ 4], 20, 0xe7d3fbc8); /* 24 */GG(a, b, c, d, x[ 9], 5, 0x21e1cde6); /* 25 */GG(d, a, b, c, x[14], 9, 0xc33707d6); /* 26 */GG(c, d, a, b, x[ 3], 14, 0xf4d50d87); /* 27 */GG(b, c, d, a, x[ 8], 20, 0x455a14ed); /* 28 */GG(a, b, c, d, x[13], 5, 0xa9e3e905); /* 29 */GG(d, a, b, c, x[ 2], 9, 0xfcefa3f8); /* 30 */GG(c, d, a, b, x[ 7], 14, 0x676f02d9); /* 31 */GG(b, c, d, a, x[12], 20, 0x8d2a4c8a); /* 32 *//* Round 3 */HH(a, b, c, d, x[ 5], 4, 0xfffa3942); /* 33 */HH(d, a, b, c, x[ 8], 11, 0x8771f681); /* 34 */HH(c, d, a, b, x[11], 16, 0x6d9d6122); /* 35 */HH(b, c, d, a, x[14], 23, 0xfde5380c); /* 36 */HH(a, b, c, d, x[ 1], 4, 0xa4beea44); /* 37 */HH(d, a, b, c, x[ 4], 11, 0x4bdecfa9); /* 38 */HH(c, d, a, b, x[ 7], 16, 0xf6bb4b60); /* 39 */HH(b, c, d, a, x[10], 23, 0xbebfbc70); /* 40 */HH(a, b, c, d, x[13], 4, 0x289b7ec6); /* 41 */HH(d, a, b, c, x[ 0], 11, 0xeaa127fa); /* 42 */HH(c, d, a, b, x[ 3], 16, 0xd4ef3085); /* 43 */HH(b, c, d, a, x[ 6], 23, 0x4881d05); /* 44 */HH(a, b, c, d, x[ 9], 4, 0xd9d4d039); /* 45 */HH(d, a, b, c, x[12], 11, 0xe6db99e5); /* 46 */HH(c, d, a, b, x[15], 16, 0x1fa27cf8); /* 47 */HH(b, c, d, a, x[ 2], 23, 0xc4ac5665); /* 48 *//* Round 4 */II(a, b, c, d, x[ 0], 6, 0xf4292244); /* 49 */II(d, a, b, c, x[ 7], 10, 0x432aff97); /* 50 */II(c, d, a, b, x[14], 15, 0xab9423a7); /* 51 */II(b, c, d, a, x[ 5], 21, 0xfc93a039); /* 52 */II(a, b, c, d, x[12], 6, 0x655b59c3); /* 53 */II(d, a, b, c, x[ 3], 10, 0x8f0ccc92); /* 54 */II(c, d, a, b, x[10], 15, 0xffeff47d); /* 55 */II(b, c, d, a, x[ 1], 21, 0x85845dd1); /* 56 */II(a, b, c, d, x[ 8], 6, 0x6fa87e4f); /* 57 */II(d, a, b, c, x[15], 10, 0xfe2ce6e0); /* 58 */II(c, d, a, b, x[ 6], 15, 0xa3014314); /* 59 */II(b, c, d, a, x[13], 21, 0x4e0811a1); /* 60 */II(a, b, c, d, x[ 4], 6, 0xf7537e82); /* 61 */II(d, a, b, c, x[11], 10, 0xbd3af235); /* 62 */II(c, d, a, b, x[ 2], 15, 0x2ad7d2bb); /* 63 */II(b, c, d, a, x[ 9], 21, 0xeb86d391); /* 64 */state[0] += a;state[1] += b;state[2] += c;state[3] += d;}
测试文件——test.c
#include <stdio.h>#include <string.h>#include <stdlib.h>#include "md5.h"int main(int argc, char *argv[]){int i;unsigned char encrypt[] ="admin";//21232f297a57a5a743894a0e4a801fc3unsigned char decrypt[16]; MD5_CTX md5;MD5Init(&md5); MD5Update(&md5,encrypt,strlen((char *)encrypt));MD5Final(&md5,decrypt); printf("加密前:%s\n加密后:",encrypt);for(i=0;i<16;i++){printf("%02x",decrypt[i]);}getchar();return 0;}
亲身测试，发现一下问题：
1、test文件内有strlen（）函数，头文件中应该引用响应的函数库#include <string.h>
执行命令：
[root@localhost md5]# gcc -g test.c md5.c -o md5
执行结果：
温馨提示：
可以用md5在线解密破解,md5解密加密网址进行测试，结果的正确与否。
参考链接：/xhhjin/article/details/8450686
