C++实现MD5

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#include#include#include#include 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;}