MD5算法理论和实现

来源：互联网发布：网络运营许可证编辑：程序博客网时间：2024/05/21 08:49

MD5是消息摘要算法第5版，它是一种在计算机安全领域广泛使用的一种散列函数，用来提供消息完整性保护。任意长度的数据算出来的MD5值长度都是一样的，均为128bit，而且即使只修改原始数据的极小一部分，也会使算出的MD5值产生很大的变化。十年前，2005年山东大学的王小云教授发表论文说可以破解MD5码。但目前MD5码的应用还是挺广泛的，可能不久的将来会有新的算法取代其。

MD5算法理论

填充：填充到512位的整数倍，N*512+448，最后64位存放原始数据比特位的长度
初始化变量：链接变量等
分组处理：以512位为单位，进行计算
详细的理论介绍见百度百科: 点击

MD5算法实现

参考网上的代码，自己加入了一些注释：

#include<iostream>#include<math.h>#include<string>#include<vector>using namespace std;int ROL(int x, int s) //循环移位要考虑符号的问题{    int temp1 = x << s;    int temp2 = x >> (32 - s);    int temp3 = 0;    for(int i = 0; i<s; i++)    {        temp3 += temp2 & (1<<i);    }    return temp1 | temp3;}int F(int x ,int y, int z){    return (x & y) | ((~x) & z);}int G(int x, int y, int z){    return (x & z) | (y & (~z));}int H(int x, int y, int z){    return x ^ y ^ z;}int I(int x, int y, int z){    return y ^ (x | (~z));}void FF(int &a, int b, int c, int d, int m, unsigned char s, int ti){    a = a + F(b, c, d) + m + ti;    a = ROL(a, s);    a += b;}void GG(int &a, int b, int c, int d, int m, unsigned char s, int ti){    a = a + G(b, c, d) + m + ti;    a = ROL(a, s);    a += b;}void HH(int &a, int b, int c, int d, int m, unsigned char s,int ti){    a = a + H(b, c, d) + m + ti;    a = ROL(a, s);    a += b;}void II(int &a, int b, int c, int d, int m, unsigned char s, int ti){    a = a + I(b, c, d) + m + ti;    a = ROL(a, s);    a += b;}void output(int a) //以小端规则输出{     for(int i = 0; i<4; i++)    {        int temp = a & 0xff;        if( temp < 16)        {        cout<<"0";        }        printf("%x",temp);        a = a >> 8;    }}int main(){    vector<int*> v;    string s1="message digest";    cout<<"请输入需要加密的信息："<<endl;    getline(cin,s1);    int A,B,C,D,a,b,c,d;    //初始化四个链接变量A,B,C,D    A = 0x67452301;    B = 0xefcdab89;    C = 0x98badcfe;    D = 0x10325476;    int bits,len = s1.length(),i,j,p,counter = 0,num;    bits = len * 8;    //字符串长度    p=1;    for(i = 0; i<len; )    {        int M[16];        for(j = 0; j < 16; j++)        {            if(4*p-1 < len)   // 每4个字符组成一个整型值             {                num = 4*p-1;            }            else            {                num = len-1;            }            counter = 0;            M[j] = s1[num];            counter++;            i++;            for(; counter < 4; counter++)  //4个字符一组中，进行移位操作             {                if(i >= len) break;                M[j] = M[j] << 8;                 M[j] += s1[num - counter];                i++;            }            p++;            if(i >= len) break;        }        if(j < 16)  //出现不足512位的情况，即原始字符串转换成比特位数，不是512的整数倍         {            for(int k = j+1; k<16; k++)            {                M[k] = 0;            }            if( counter < 4)            {                M[j] += 0x80 << (counter*8);            }            else   //有四个字符             {                j++;                M[j] += 0x80;            }            if(j < 14)  // 即小于448             {                M[14] = bits & 0x00000000ffffffffULL; //声明该数为无符号长长整形，64bit                 M[15] = bits & 0xffffffff00000000ULL;                v.push_back(M);            }            else   //大于等于448             {                v.push_back(M);                int N[16];                for(int k = 0; k<14; k++)                {                    N[k] = 0;                }                N[14] = bits & 0x00000000ffffffffULL;                N[15] = bits & 0xffffffff00000000ULL;                v.push_back(N);            }        }    }    //考虑空字符串的情况    if( s1.length() == 0)    {        int M[16];        M[0] = 0x00000080;        for(int n = 1; n<16; n++)        {            M[n] = 0;        }        v.push_back(M);    }    vector<int*>::iterator it;    //主循环    for(it = v.begin(); it != v.end(); it++)    {        a = A; b = B; c = C; d = D;        //第一轮        FF(a,b,c,d,(*it)[0],7,0xd76aa478);        FF(d,a,b,c,(*it)[1],12,0xe8c7b756);        FF(c,d,a,b,(*it)[2],17,0x242070db);         FF(b,c,d,a,(*it)[3],22,0xc1bdceee);        FF(a,b,c,d,(*it)[4],7,0xf57c0faf);        FF(d,a,b,c,(*it)[5],12,0x4787c62a);         FF(c,d,a,b,(*it)[6],17,0xa8304613);        FF(b,c,d,a,(*it)[7],22,0xfd469501) ;        FF(a,b,c,d,(*it)[8],7,0x698098d8) ;        FF(d,a,b,c,(*it)[9],12,0x8b44f7af) ;        FF(c,d,a,b,(*it)[10],17,0xffff5bb1) ;        FF(b,c,d,a,(*it)[11],22,0x895cd7be) ;        FF(a,b,c,d,(*it)[12],7,0x6b901122) ;        FF(d,a,b,c,(*it)[13],12,0xfd987193) ;        FF(c,d,a,b,(*it)[14],17,0xa679438e) ;        FF(b,c,d,a,(*it)[15],22,0x49b40821);        //第二轮        GG(a,b,c,d,(*it)[1],5,0xf61e2562);         GG(d,a,b,c,(*it)[6],9,0xc040b340);         GG(c,d,a,b,(*it)[11],14,0x265e5a51);         GG(b,c,d,a,(*it)[0],20,0xe9b6c7aa) ;        GG(a,b,c,d,(*it)[5],5,0xd62f105d) ;        GG(d,a,b,c,(*it)[10],9,0x02441453) ;        GG(c,d,a,b,(*it)[15],14,0xd8a1e681);         GG(b,c,d,a,(*it)[4],20,0xe7d3fbc8) ;        GG(a,b,c,d,(*it)[9],5,0x21e1cde6) ;        GG(d,a,b,c,(*it)[14],9,0xc33707d6) ;        GG(c,d,a,b,(*it)[3],14,0xf4d50d87) ;        GG(b,c,d,a,(*it)[8],20,0x455a14ed);         GG(a,b,c,d,(*it)[13],5,0xa9e3e905);         GG(d,a,b,c,(*it)[2],9,0xfcefa3f8) ;        GG(c,d,a,b,(*it)[7],14,0x676f02d9) ;        GG(b,c,d,a,(*it)[12],20,0x8d2a4c8a);        //第三轮        HH(a,b,c,d,(*it)[5],4,0xfffa3942);         HH(d,a,b,c,(*it)[8],11,0x8771f681);         HH(c,d,a,b,(*it)[11],16,0x6d9d6122);         HH(b,c,d,a,(*it)[14],23,0xfde5380c) ;        HH(a,b,c,d,(*it)[1],4,0xa4beea44) ;        HH(d,a,b,c,(*it)[4],11,0x4bdecfa9) ;        HH(c,d,a,b,(*it)[7],16,0xf6bb4b60) ;        HH(b,c,d,a,(*it)[10],23,0xbebfbc70);         HH(a,b,c,d,(*it)[13],4,0x289b7ec6);         HH(d,a,b,c,(*it)[0],11,0xeaa127fa);         HH(c,d,a,b,(*it)[3],16,0xd4ef3085);         HH(b,c,d,a,(*it)[6],23,0x04881d05);         HH(a,b,c,d,(*it)[9],4,0xd9d4d039);         HH(d,a,b,c,(*it)[12],11,0xe6db99e5);         HH(c,d,a,b,(*it)[15],16,0x1fa27cf8);        HH(b,c,d,a,(*it)[2],23,0xc4ac5665);        //第四轮        II(a,b,c,d,(*it)[0],6,0xf4292244) ;        II(d,a,b,c,(*it)[7],10,0x432aff97) ;        II(c,d,a,b,(*it)[14],15,0xab9423a7);         II(b,c,d,a,(*it)[5],21,0xfc93a039) ;        II(a,b,c,d,(*it)[12],6,0x655b59c3) ;        II(d,a,b,c,(*it)[3],10,0x8f0ccc92) ;        II(c,d,a,b,(*it)[10],15,0xffeff47d);         II(b,c,d,a,(*it)[1],21,0x85845dd1) ;        II(a,b,c,d,(*it)[8],6,0x6fa87e4f) ;        II(d,a,b,c,(*it)[15],10,0xfe2ce6e0);         II(c,d,a,b,(*it)[6],15,0xa3014314);        II(b,c,d,a,(*it)[13],21,0x4e0811a1);         II(a,b,c,d,(*it)[4],6,0xf7537e82) ;        II(d,a,b,c,(*it)[11],10,0xbd3af235);         II(c,d,a,b,(*it)[2],15,0x2ad7d2bb);         II(b,c,d,a,(*it)[9],21,0xeb86d391);        A += a;        B += b;        C += c;        D += d;    }    cout<<"MD5 = ";    output(A);    output(B);    output(C);    output(D);    cout<<endl;    return 0;}

参考文献

MD5加密C++实现代码实例
MD5算法步骤详解

0 0