MD5解密方法(常见的MD5解密方法)

一、MD5算法原理

MD5算法是一种单向加密算法，可以把任意长度的消息通过一定的算法，变成一个128位的十六进制数字串。这个过程是不可逆的，也就是说无法从加密后的结果推算出加密前的原始数据。

MD5算法的核心是4个函数，分别为F、G、H、I。这些函数都是基于位运算的逻辑函数，其实现方式比较简单。


/*用于计算MD5第1轮到第16轮的函数*/
#define FF(a,b,c,d,X,s,ac) { 
 (a)+=F((b),(c),(d))+(X)+(ac);  
 (a)=ROTATE_LEFT((a),(s)); 
 (a)+=(b); 
}
 
/*用于计算MD5第17轮到第32轮的函数*/
#define GG(a,b,c,d,X,s,ac) { 
 (a)+=G((b),(c),(d))+(X)+(ac); 
 (a)=ROTATE_LEFT((a),(s)); 
 (a)+=(b); 
}
 
/*用于计算MD5第33轮到第48轮的函数*/
#define HH(a,b,c,d,X,s,ac) { 
 (a)+=H((b),(c),(d))+(X)+(ac);  
 (a)=ROTATE_LEFT((a),(s)); 
 (a)+=(b); 
}
 
/*用于计算MD5第49轮到第64轮的函数*/
#define II(a,b,c,d,X,s,ac) { 
 (a)+=I((b),(c),(d))+(X)+(ac);  
 (a)=ROTATE_LEFT((a),(s)); 
 (a)+=(b); 
}

二、MD5算法的应用场景

由于MD5算法可以将任意长度的数据加密成固定长度的数字串，因此它非常适合在数据传输过程中进行应用。比如在网站用户注册时，可以将用户的密码使用MD5算法加密储存，这样即使服务器被攻击，黑客也无法直接获得用户的密码。

此外，MD5算法还可以用作数字签名、文件校验、数据完整性校验等方面的应用。在实际开发中，我们可以在文件传输、数据备份、软件升级等场景下使用MD5算法来保证传输过程中数据的完整性和准确性。

三、MD5算法的破解和攻击

MD5算法虽然可以将密码等敏感信息加密，但它不是绝对安全的。在理论上，MD5算法是可以被破解的。其主要原因是MD5算法本身存在一些漏洞，攻击者可以利用这些漏洞来实现暴力破解、彩虹表攻击等方式对MD5加密后的数据进行破解。

因此，在实际开发中，我们需要采取一系列的安全措施来保护数据的安全。比如使用更为高级的加密算法来保护数据、限制用户的登录次数和频率、强制用户使用强密码等。

四、MD5算法的代码示例

下面是一个使用C++语言实现的MD5算法示例：



#include

#include

#include

const unsigned int S[64]={

    7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22,

    5, 9, 14, 20, 5, 9, 14, 20, 5, 9, 14, 20, 5, 9, 14, 20,

    4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23,

    6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21

};

const unsigned int K[64]={

    0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee,

    0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501,

    0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be,

    0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821,

    0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa,

    0xd62f105d, 0x2441453, 0xd8a1e681, 0xe7d3fbc8,

    0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed,

    0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a,

    0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c,

    0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,

    0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x4881d05,

    0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665,

    0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039,

    0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1,

    0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1,

    0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391

};

using namespace std;

unsigned int A, B, C, D;

//前向声明

unsigned int F(unsigned int X, unsigned int Y, unsigned int Z);

unsigned int G(unsigned int X, unsigned int Y, unsigned int Z);

unsigned int H(unsigned int X, unsigned int Y, unsigned int Z);

unsigned int I(unsigned int X, unsigned int Y, unsigned int Z);

void FF(unsigned int& a,unsigned int b,unsigned int c,unsigned int d,unsigned int Mj, unsigned int s, unsigned int ti);

void GG(unsigned int& a,unsigned int b,unsigned int c,unsigned int d,unsigned int Mj, unsigned int s, unsigned int ti);

void HH(unsigned int& a,unsigned int b,unsigned int c,unsigned int d,unsigned int Mj, unsigned int s, unsigned int ti);

void II(unsigned int& a,unsigned int b,unsigned int c,unsigned int d,unsigned int Mj, unsigned int s, unsigned int ti);

//置换函数

unsigned int F(unsigned int X,unsigned int Y,unsigned int Z){

    return ((X)&(Y))|(~(X)&(Z));

}

unsigned int G(unsigned int X,unsigned int Y,unsigned int Z){

    return ((X)&(Z))|((Y)&~(Z));

}

unsigned int H(unsigned int X,unsigned int Y,unsigned int Z){

    return (X)^(Y)^(Z);

}

unsigned int I(unsigned int X,unsigned int Y,unsigned int Z){

    return (Y)^((X)|~(Z));

}

//循环左移函数

#define ROTATE_LEFT(x,n) ((x)<>(32-(n)))

//将数转换为十六进制字符串

void ToHex(const unsigned char* input,unsigned int len,char* output){

    const char* table = "0123456789abcdef";

    for(unsigned int i=0;i>4];

        output[i*2+1] = table[input[i]&0x0f];

    }

    output[len*2]=0;

}

//MD5加密

void EncryptMD5(const unsigned char* msg,unsigned int msg_len,char* output){

    unsigned long i, j;

    unsigned char bytes[64];

    unsigned int count[2] = {0, 0};

    unsigned int A, B, C, D;

    //初始化MD缓冲区

    A = 0x67452301;

    B = 0xefcdab89;

    C = 0x98badcfe;

    D = 0x10325476;

    //计算全局消息个数

    count[0] = msg_len<>29;

    //重复填充消息

    while (msg_len >= 64){

        memcpy(bytes, msg, 64);

        //1024 比特MD缓冲区更新

        FF(A,B,C,D,*((unsigned int*)bytes+ 0),S[ 0],K[ 0]);

        FF(D,A,B,C,*((unsigned int*)bytes+ 1),S[ 1],K[ 1]);

        FF(C,D,A,B,*((unsigned int*)bytes+ 2),S[ 2],K[ 2]);

        FF(B,C,D,A,*((unsigned int*)bytes+ 3),S[ 3],K[ 3]);

        FF(A,B,C,D,*((unsigned int*)bytes+ 4),S[ 4],K[ 4]);

        FF(D,A,B,C,*((unsigned int*)bytes+ 5),S[ 5],K[ 5]);

        FF(C,D,A,B,*((unsigned int*)bytes+ 6),S[ 6],K[ 6]);

        FF(B,C,D,A,*((unsigned int*)bytes+ 7),S[ 7],K[ 7]);

        FF(A,B,C,D,*((unsigned int*)bytes+ 8),S[ 8],K[ 8]);

        FF(D,A,B,C,*((unsigned int*)bytes+ 9),S[ 9],K[ 9]);

        FF(C,D,A,B,*((unsigned int*)bytes+10),S[10],K[10]);

        FF(B,C,D,A,*((unsigned int*)bytes+11),S[11],K[11]);

        FF(A,B,C,D,*((unsigned int*)bytes+12),S[12],K[12]);

        FF(D,A,B,C,*((unsigned int*)bytes+13),S[13],K[13]);

        FF(C,D,A,B,*((unsigned int*)bytes+14),S[14],K[14]);

        FF(B,C,D,A,*((unsigned int*)bytes+15),S[15],K[15]);

        msg += 64;

        msg_len -= 64;

    }

    memset(bytes,0,64);

    memcpy(bytes,msg,msg_len);

    //填充，保证消息长度为512的整数倍

    bytes[msg_len++] = 0x80;

    if(msg_len <= 56){

        memset(bytes+msg_len, 0, 56-msg_len);

    }

    else{

        memset(bytes+msg_len, 0, 64-msg_len);

        //1024 比特MD缓冲区更新

        FF(A,B,C,D,*((unsigned int*)bytes+ 0),S[ 0],K[ 0]);

        FF(D,A,B,C,*((unsigned int*)bytes+ 1),S[ 1],K[ 1]);

        FF(C,D,A,B,*((unsigned int*)bytes+ 2),S[ 2],K[ 2]);

        FF(B,C,D,A,*((unsigned int*)bytes+ 3),S[ 3],K[ 3]);

        FF(A,B,C,D,*((unsigned int*)bytes+ 4),S[ 4],K[ 4]);

        FF(D,A,B,C,*((unsigned int*)bytes+ 5),S[ 5],K[ 5]);

        FF(C,D,A,B,*((unsigned int*)bytes+ 6),S[ 6],K[ 6]);

        FF(B,C,D,A,*((unsigned int*)bytes+ 7),S[ 7],K[ 7]);

        FF(A,B,C,D,*((unsigned int*)bytes+ 8),S[ 8],K[ 8]);

        FF(D,A,B,C,*((unsigned int*)bytes+ 9),S[ 9],K[

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