md5-info

MD5

MD5信息摘要算法(英语:MD5 Message-Digest Algorithm),一种被广泛使用的密码散列函数,可以产生出一个128位(16字节)的散列值(hash value),用于确保信息传输完整一致。MD5由美国密码学家罗纳德·李维斯特(Ronald Linn Rivest)设计,于1992年公开,用以取代MD4算法。这套算法的程序在 RFC 1321 标准中被加以规范。1996年后该算法被证实存在弱点,可以被加以破解,对于需要高度安全性的数据,专家一般建议改用其他算法,如SHA-2。2004年,证实MD5算法无法防止碰撞(collision),因此不适用于安全性认证,如SSL公开密钥认证或是数字签名等用途。

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C++实现

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#include<iostream>
#include<string>
using namespace std;
#define shift(x, n) (((x) << (n)) | ((x) >> (32-(n))))//右移的时候,高位一定要补零,而不是补充符号位
#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)))
#define A 0x67452301
#define B 0xefcdab89
#define C 0x98badcfe
#define D 0x10325476
//strBaye的长度
unsigned int strlength;
//A,B,C,D的临时变量
unsigned int atemp;
unsigned int btemp;
unsigned int ctemp;
unsigned int dtemp;
//常量ti unsigned int(abs(sin(i+1))*(2pow32))
const unsigned int k[]={
0xd76aa478,0xe8c7b756,0x242070db,0xc1bdceee,
0xf57c0faf,0x4787c62a,0xa8304613,0xfd469501,0x698098d8,
0x8b44f7af,0xffff5bb1,0x895cd7be,0x6b901122,0xfd987193,
0xa679438e,0x49b40821,0xf61e2562,0xc040b340,0x265e5a51,
0xe9b6c7aa,0xd62f105d,0x02441453,0xd8a1e681,0xe7d3fbc8,
0x21e1cde6,0xc33707d6,0xf4d50d87,0x455a14ed,0xa9e3e905,
0xfcefa3f8,0x676f02d9,0x8d2a4c8a,0xfffa3942,0x8771f681,
0x6d9d6122,0xfde5380c,0xa4beea44,0x4bdecfa9,0xf6bb4b60,
0xbebfbc70,0x289b7ec6,0xeaa127fa,0xd4ef3085,0x04881d05,
0xd9d4d039,0xe6db99e5,0x1fa27cf8,0xc4ac5665,0xf4292244,
0x432aff97,0xab9423a7,0xfc93a039,0x655b59c3,0x8f0ccc92,
0xffeff47d,0x85845dd1,0x6fa87e4f,0xfe2ce6e0,0xa3014314,
0x4e0811a1,0xf7537e82,0xbd3af235,0x2ad7d2bb,0xeb86d391};
//向左位移数
const unsigned int s[]={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 char str16[]="0123456789abcdef";
void mainLoop(unsigned int M[])
{
unsigned int f,g;
unsigned int a=atemp;
unsigned int b=btemp;
unsigned int c=ctemp;
unsigned int d=dtemp;
for (unsigned int i = 0; i < 64; i++)
{
if(i<16){
f=F(b,c,d);
g=i;
}else if (i<32)
{
f=G(b,c,d);
g=(5*i+1)%16;
}else if(i<48){
f=H(b,c,d);
g=(3*i+5)%16;
}else{
f=I(b,c,d);
g=(7*i)%16;
}
unsigned int tmp=d;
d=c;
c=b;
b=b+shift((a+f+k[i]+M[g]),s[i]);
a=tmp;
}
atemp=a+atemp;
btemp=b+btemp;
ctemp=c+ctemp;
dtemp=d+dtemp;
}
/*
*填充函数
*处理后应满足bits≡448(mod512),字节就是bytes≡56(mode64)
*填充方式为先加一个1,其它位补零
*最后加上64位的原来长度
*/
unsigned int* add(string str)
{
unsigned int num=((str.length()+8)/64)+1;//以512位,64个字节为一组
unsigned int *strByte=new unsigned int[num*16]; //64/4=16,所以有16个整数
strlength=num*16;
for (unsigned int i = 0; i < num*16; i++)
strByte[i]=0;
for (unsigned int i=0; i <str.length(); i++)
{
strByte[i>>2]|=(str[i])<<((i%4)*8);//一个整数存储四个字节,i>>2表示i/4 一个unsigned int对应4个字节,保存4个字符信息
}
strByte[str.length()>>2]|=0x80<<(((str.length()%4))*8);//尾部添加1 一个unsigned int保存4个字符信息,所以用128左移
/*
*添加原长度,长度指位的长度,所以要乘8,然后是小端序,所以放在倒数第二个,这里长度只用了32位
*/
strByte[num*16-2]=str.length()*8;
return strByte;
}
string changeHex(int a)
{
int b;
string str1;
string str="";
for(int i=0;i<4;i++)
{
str1="";
b=((a>>i*8)%(1<<8))&0xff; //逆序处理每个字节
for (int j = 0; j < 2; j++)
{
str1.insert(0,1,str16[b%16]);
b=b/16;
}
str+=str1;
}
return str;
}
string getMD5(string source)
{
atemp=A; //初始化
btemp=B;
ctemp=C;
dtemp=D;
unsigned int *strByte=add(source);
for(unsigned int i=0;i<strlength/16;i++)
{
unsigned int num[16];
for(unsigned int j=0;j<16;j++)
num[j]=strByte[i*16+j];
mainLoop(num);
}
return changeHex(atemp).append(changeHex(btemp)).append(changeHex(ctemp)).append(changeHex(dtemp));
}
unsigned int main()
{
string ss;
// cin>>ss;
string s=getMD5("abc");
cout<<s;
return 0;
}
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