MD5算法实现

md5.h

#ifndef MD5_H#define MD5_Htypedef struct{unsigned int count[2];/* 位数量, 模 2^64 (低位在前) */unsigned int state[4];/* state (ABCD) */unsigned char buffer[64];/* 输入缓冲器 */}MD5_CTX;//非线性辅助函数#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))/* ROTATE_LEFT 将x循环左移n位 */#define ROTATE_LEFT(x,n) ((x << n) | (x >> (32-n)))/* 循环从加法中分离出是为了防止重复计算*/#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; \          }/*初始化md5的结构*/void MD5Init(MD5_CTX *context);/*将与加密的信息传递给md5结构，可以多次调用context：初始化过了的md5结构input：欲加密的信息，可以任意长inputLen：指定input的长度*/void MD5Update(MD5_CTX *context, unsigned char *input, unsigned int inputlen);/*获取加密 的最终结果digest：保存最终的加密串context：你前面初始化并填入了信息的md5结构*/void MD5Final(MD5_CTX *context, unsigned char digest[16]);/*对512bits信息(即block缓冲区)进行一次处理，每次处理包括四轮state[4]：md5结构中的state[4]，用于保存对512bits信息加密的中间结果或者最终结果block[64]：欲加密的512bits信息*/void MD5Transform(unsigned int state[4], unsigned char block[64]);/*字节转换函数output：用于输出的字符缓冲区input：欲转换的四字节的整数形式的数组len：output缓冲区的长度，要求是4的整数倍*/void MD5Encode(unsigned char *output, unsigned int *input, unsigned int len);/*与上面相反的转换函数output：保存转换出的整数input：欲转换的字符缓冲区len：输入的字符缓冲区的长度，要求是4的整数倍*/void MD5Decode(unsigned int *output, unsigned char *input, unsigned int len);#endif

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 };/*初始化md5的结构*/void MD5Init(MD5_CTX *context){/*将当前的有效信息的长度设成0,这个很简单,还没有有效信息,长度当然是0了*/context->count[0] = 0;context->count[1] = 0;/* Load magic initialization constants.*//*初始化变量，算法要求这样 */context->state[0] = 0x67452301;context->state[1] = 0xEFCDAB89;context->state[2] = 0x98BADCFE;context->state[3] = 0x10325476;}/*将与加密的信息传递给md5结构，可以多次调用context：初始化过了的md5结构input：欲加密的信息，可以任意长inputLen：指定input的长度*/void MD5Update(MD5_CTX *context, unsigned char *input, unsigned int inputlen){unsigned int i = 0, index = 0, partlen = 0;/* Compute number of bytes mod 64 *//**计算已有信息的bits长度的字节数的模64, 64bytes=512bits。*  用于判断已有信息加上当前传过来的信息的总长度能不能达到512bits，*  如果能够达到则对凑够的512bits进行一次处理*//*计算已有信息模64后的字节数*/index = (context->count[0] >> 3) & 0x3F;/*计算已有的字节数长度还差多少字节可以凑成64字节的整倍数*/partlen = 64 - index;/* Update number of bits *//* 更新已有信息的bits长度，当已有长度加上新输入信息的长度*  如果小于新输入的信息长度，说明高位进位*/context->count[0] += inputlen << 3;if (context->count[0] < (inputlen << 3))context->count[1]++;context->count[1] += inputlen >> 29;//输入的高位字节数/* Transform as many times as possible.*//*如果当前输入的字节数 大于 已有字节数长度补足64字节整倍数所差的字节数*/if (inputlen >= partlen){/*用当前输入的内容把context->buffer的内容补足512bits*/memcpy(&context->buffer[index], input, partlen);/*用基本函数对填充满的512bits（已经保存到context->buffer中） 做一次转换，转换结果保存到context->state中*/MD5Transform(context->state, context->buffer);/*对当前输入的剩余字节（满足512bits）做转换,转换结果保存到context->state中*/for (i = partlen; i + 64 <= inputlen; i += 64)/*改为i+64<=inputlen更容易理解*/MD5Transform(context->state, &input[i]);index = 0;}else{i = 0;}/* Buffer remaining input *//*将输入缓冲区中不足512bits的剩余内容填充到context->buffer中，留待以后再作处理*/memcpy(&context->buffer[index], &input[i], inputlen - i);}/*获取加密 的最终结果digest：保存最终的加密串context：你前面初始化并填入了信息的md5结构*/void MD5Final(MD5_CTX *context, unsigned char digest[16]){unsigned int index = 0, padlen = 0;unsigned char bits[8];/* 计算已有的bits长度的字节数的模64, 64bytes=512bits*/index = (context->count[0] >> 3) & 0x3F;/*计算需要填充的字节数，padLen的取值范围在1-64之间*/padlen = (index < 56) ? (56 - index) : (120 - index);/*将要被转换的信息转换成8bits的字符串*/MD5Encode(bits, context->count, 8);/*这一次函数调用至多导致一次MD5Transform调用，因为这一次填充后的大小为：48~64+48字节数*/MD5Update(context, PADDING, padlen);/*补上原始信息的bits长度（bits长度固定的用64bits表示），这一次能够恰巧凑够512bits，不会多也不会少*/MD5Update(context, bits, 8);/*将最终的结果保存到digest中，将4个32bits转换成16个8bits*/MD5Encode(digest, context->state, 16);}/*字节转换函数(unsigned int * TO unsigned char *)output：用于输出的字符缓冲区input：欲转换的四字节的整数形式的数组len：output缓冲区的长度，要求是4的整数倍*/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;}}/*与上面相反的转换函数((unsigned char * TO unsigned int *))output：保存转换出的整数input：欲转换的字符缓冲区len：输入的字符缓冲区的长度，要求是4的整数倍*/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;}}/*对512bits信息(即block缓冲区)进行一次处理，每次处理包括四轮state[4]：md5结构中的state[4]，用于保存对512bits信息加密的中间结果或者最终结果block[64]：欲加密的512bits信息*/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;}

test.cpp

#include <stdio.h>  #include <stdlib.h>#include <string.h>extern "C"{#include "md5.h"};int main(int argc, char *argv[]){int i;unsigned char encrypt[] = "admin";unsigned char decrypt[16];MD5_CTX md5;MD5Init(&md5);MD5Update(&md5, encrypt, strlen((char *)encrypt));MD5Final(&md5, decrypt);printf("加密前:%s\n", encrypt);printf("加密后:");for (i = 0; i < 16; i++){printf("%02x", decrypt[i]);}putchar('\n');return 0;}