以下代码是自己用C++语言对MD5算法的实现，编程工具是VC2013。虽然代码的封装性、安全性和效率远远比不上RFC文档中的标准实现或者OpenSSL的源码（这些代码研究了很久依旧没看懂，它们的效率虽
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以下代码是自己用C++语言对MD5算法的实现，编程工具是VC2013。虽然代码的封装性、安全性和效率远远比不上RFC文档中的标准实现或者OpenSSL的源码（这些代码研究了很久依旧没看懂，它们的效率虽高，但可读性不高，不适合于我这种基础比较薄弱的童鞋阅读），但算法思路比较直观，清晰易懂，方便让基础比较薄弱的童鞋阅读。本人属于C++初学者，编写的代码可能不够简洁，不够美观，很多地方也没有考虑周到，希望大家见谅，也希望能有高手能指正批评。
注意：每处理64个字符就进行一次MD5操作，MD5算法本身不算太难，主要是输入消息的预处理过程比较麻烦。
#pragma warning(disable : 4996)//VC2013增加了安全机制，如果不加这句会出现编译错误#include<iostream>#include<string>#include<stdio.h>#include<stdlib.h>#include <bitset>using namespace std;typedef unsigned int UNINT;//为unsigned int重命名，方便编程#define S11 7#define S12 12#define S13 17#define S14 22#define S21 5#define S22 9#define S23 14#define S24 20#define S31 4#define S32 11#define S33 16#define S34 23#define S41 6#define S42 10#define S43 15#define S44 21UNINT hash_state[4];UNINT word_32[16];char block[64];//初始化向量（A,B,C,D）void Init(){ hash_state[0] = 0x67452301; hash_state[1] = 0xefcdab89; hash_state[2] = 0x98badcfe; hash_state[3] = 0x10325476;}//将长度为64的字符数组转换成长度为16的整型数组，即将四个字符数组单元转换为一个整型数组int char64_to_word32(int n){ int i; for (i = 0; i < n; i++){ word_32[i] = (block[4 * i + 0] << 24) ^ (block[4 * i + 1] << 16) ^ (block[4 * i + 2] << 8) ^ block[4 * i + 3]; } return i;}//新建一个分组存放消息长度void newblock_length(UNINT l){ for (int i = 0; i < 15; i++){ word_32[i] = 0; } //将消息长度存放在最后4个字节 word_32[15] = l;}UNINT rotate_left(UNINT x, UNINT n){ return ((x << n) | (x >> (32 - n)));}UNINT F(UNINT x, UNINT y, UNINT z){ return ((x & y) | (~x & z));}UNINT G(UNINT x, UNINT y, UNINT z){ return ((x & z) | (y & ~z));}UNINT H(UNINT x, UNINT y, UNINT z){ return (x ^ y ^ z);}UNINT I(UNINT x, UNINT y, UNINT z){ return (y ^ (x | ~z));}void FF(UNINT* a, UNINT b, UNINT c, UNINT d, UNINT x, UNINT s, UNINT ac){ *a += F(b, c, d) + x + ac; *a = rotate_left(*a, s); *a += b;}void GG(UNINT* a, UNINT b, UNINT c, UNINT d, UNINT x, UNINT s, UNINT ac){ *a += G(b, c, d) + x + ac; *a = rotate_left(*a, s); *a += b;}void HH(UNINT* a, UNINT b, UNINT c, UNINT d, UNINT x, UNINT s, UNINT ac){ *a += H(b, c, d) + x + ac; *a = rotate_left(*a, s); *a += b;}void II(UNINT* a, UNINT b, UNINT c, UNINT d, UNINT x, UNINT s, UNINT ac){ *a += I(b, c, d) + x + ac; *a = rotate_left(*a, s); *a += b;}void MD5_Transform(UNINT* x){ UNINT a, b, c, d; a = hash_state[0]; b = hash_state[1]; c = hash_state[2]; d = hash_state[3]; // Round 1 FF(&a, b, c, d, x[0], S11, 0xd76aa478); FF(&d, a, b, c, x[1], S12, 0xe8c7b756); FF(&c, d, a, b, x[2], S13, 0x242070db); FF(&b, c, d, a, x[3], S14, 0xc1bdceee); FF(&a, b, c, d, x[4], S11, 0xf57c0faf); FF(&d, a, b, c, x[5], S12, 0x4787c62a); FF(&c, d, a, b, x[6], S13, 0xa8304613); FF(&b, c, d, a, x[7], S14, 0xfd469501); FF(&a, b, c, d, x[8], S11, 0x698098d8); FF(&d, a, b, c, x[9], S12, 0x8b44f7af); FF(&c, d, a, b, x[10], S13, 0xffff5bb1); FF(&b, c, d, a, x[11], S14, 0x895cd7be); FF(&a, b, c, d, x[12], S11, 0x6b901122); FF(&d, a, b, c, x[13], S12, 0xfd987193); FF(&c, d, a, b, x[14], S13, 0xa679438e); FF(&b, c, d, a, x[15], S14, 0x49b40821); // Round 2 GG(&a, b, c, d, x[1], S21, 0xf61e2562); GG(&d, a, b, c, x[6], S22, 0xc040b340); GG(&c, d, a, b, x[11], S23, 0x265e5a51); GG(&b, c, d, a, x[0], S24, 0xe9b6c7aa); GG(&a, b, c, d, x[5], S21, 0xd62f105d); GG(&d, a, b, c, x[10], S22, 0x2441453); GG(&c, d, a, b, x[15], S23, 0xd8a1e681); GG(&b, c, d, a, x[4], S24, 0xe7d3fbc8); GG(&a, b, c, d, x[9], S21, 0x21e1cde6); GG(&d, a, b, c, x[14], S22, 0xc33707d6); GG(&c, d, a, b, x[3], S23, 0xf4d50d87); GG(&b, c, d, a, x[8], S24, 0x455a14ed); GG(&a, b, c, d, x[13], S21, 0xa9e3e905); GG(&d, a, b, c, x[2], S22, 0xfcefa3f8); GG(&c, d, a, b, x[7], S23, 0x676f02d9); GG(&b, c, d, a, x[12], S24, 0x8d2a4c8a); // Round 3 HH(&a, b, c, d, x[5], S31, 0xfffa3942); HH(&d, a, b, c, x[8], S32, 0x8771f681); HH(&c, d, a, b, x[11], S33, 0x6d9d6122); HH(&b, c, d, a, x[14], S34, 0xfde5380c); HH(&a, b, c, d, x[1], S31, 0xa4beea44); HH(&d, a, b, c, x[4], S32, 0x4bdecfa9); HH(&c, d, a, b, x[7], S33, 0xf6bb4b60); HH(&b, c, d, a, x[10], S34, 0xbebfbc70); HH(&a, b, c, d, x[13], S31, 0x289b7ec6); HH(&d, a, b, c, x[0], S32, 0xeaa127fa); HH(&c, d, a, b, x[3], S33, 0xd4ef3085); HH(&b, c, d, a, x[6], S34, 0x4881d05); HH(&a, b, c, d, x[9], S31, 0xd9d4d039); HH(&d, a, b, c, x[12], S32, 0xe6db99e5); HH(&c, d, a, b, x[15], S33, 0x1fa27cf8); HH(&b, c, d, a, x[2], S34, 0xc4ac5665); // Round 4 II(&a, b, c, d, x[0], S41, 0xf4292244); II(&d, a, b, c, x[7], S42, 0x432aff97); II(&c, d, a, b, x[14], S43, 0xab9423a7); II(&b, c, d, a, x[5], S44, 0xfc93a039); II(&a, b, c, d, x[12], S41, 0x655b59c3); II(&d, a, b, c, x[3], S42, 0x8f0ccc92); II(&c, d, a, b, x[10], S43, 0xffeff47d); II(&b, c, d, a, x[1], S44, 0x85845dd1); II(&a, b, c, d, x[8], S41, 0x6fa87e4f); II(&d, a, b, c, x[15], S42, 0xfe2ce6e0); II(&c, d, a, b, x[6], S43, 0xa3014314); II(&b, c, d, a, x[13], S44, 0x4e0811a1); II(&a, b, c, d, x[4], S41, 0xf7537e82); II(&d, a, b, c, x[11], S42, 0xbd3af235); II(&c, d, a, b, x[2], S43, 0x2ad7d2bb); II(&b, c, d, a, x[9], S44, 0xeb86d391); hash_state[0] += a; hash_state[1] += b; hash_state[2] += c; hash_state[3] += d;}int main(){ UNINT word_pos, block_pos, counter, counter_update; string str ; Init();//初始化向量（A,B,C,D） cin >> str; counter = str.length();//计算输入消息的长度 counter_update = counter; block_pos = 0; //对输入消息进行分组，每组64bytes while (counter_update / 64>0){ str.copy(block, 64, 64 * block_pos);//将起始位置为64*j的后续64个字符拷贝到block数组 char64_to_word32(16);//将64个字符转换成16个字 //MD5 MD5_Transform(word_32); block_pos++; counter_update -= 64; } if (counter_update % 64 == 0){ newblock_length(counter); //MD5 MD5_Transform(word_32); } else{ //对剩余不足64bytes的分组进行处理 str.copy(block, counter_update, 64 * block_pos); //如果最后一个分组剩余不足4bytes空间来存放原始消息长度，则用0将该分组填充满，然后再新建一个分组存放消息长度 if (counter_update > 60){ //将block数组前面4k个字符转换成k个整型数 word_pos = char64_to_word32(counter_update / 4); //更新block最后剩余的字符数 counter_update -= 4 * word_pos; //根据剩余字符数模4的不同结果进行不同的处理 switch (counter_update){ case 0:{ break; } //如果最后剩余一个字符，则将其左移到最高8位，后面24位补0 case 1:{ word_32[word_pos] = (block[4 * word_pos] << 24) ^ 0x000000; word_pos++; break; } //如果最后剩余两个字符，则将其左移到最高16位，后面16位补0 case 2:{ word_32[word_pos] = (block[4 * word_pos] << 24) ^ (block[4 * word_pos + 1] << 16) ^ 0x0000; word_pos++; break; } //如果最后剩余三个字符，则将其左移到最高24位，后面8位补0 case 3:{ word_32[word_pos] = (block[4 * word_pos] << 24) ^ (block[4 * word_pos + 1] << 16) ^ (block[4 * word_pos + 2] << 8) ^ 0x00; word_pos++; break; } } //对word_36数组的剩余单元填充 while (word_pos < 16){ word_32[word_pos] = 0; word_pos++; } //MD5 MD5_Transform(word_32); //新建一个数组存放消息长度 newblock_length(counter); //MD5 MD5_Transform(word_32); } //如果最后一个分组剩余超过4bytes的空间，则用最后4bytes存放消息长度，其他位置用0填充 else{ word_pos = char64_to_word32(counter_update / 4); counter_update -= 4 * word_pos; switch (counter_update){ case 0:{ break; } case 1:{ word_32[word_pos] = (block[4 * word_pos] << 24) ^ 0x000000; word_pos++; break; } case 2:{ word_32[word_pos] = (block[4 * word_pos] << 24) ^ (block[4 * word_pos + 1] << 16) ^ 0x0000; word_pos++; break; } case 3:{ word_32[word_pos] = (block[4 * word_pos] << 24) ^ (block[4 * word_pos + 1] << 16) ^ (block[4 * word_pos + 2] << 8) ^ 0x00; word_pos++; break; } } while (word_pos < 15){ word_32[word_pos] = 0; word_pos++; } word_32[15] = counter; //MD5 MD5_Transform(word_32); } } cout << hex << hash_state[0] << endl; cout << hex << hash_state[1] << endl; cout << hex << hash_state[2] << endl; cout << hex << hash_state[3] << endl; system("pause"); return 0;}