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寻找md5值是它自己的数（下称Z数）
Z数一个128位长度的数，找到它如同大海捞针
下面代码的核心是 md5_is_self 函数，当传入的是Z数时，函数返回真
main函数里面的实现只是一个使用 md5_is_self() 例子，main函数里面的代码并不能找到Z数
#include <stdio.h>
int print_md5(const unsigned int in[4])
{
int j;
union {
unsigned int i;
unsigned char c[4];
} u;
u.i = 1;
if(u.c[0] == 1) {
// little endian
for(j = 0; j < 4; j++) {
u.i = in[j];
printf("%02x%02x%02x%02x", u.c[0], u.c[1], u.c[2], u.c[3]);
}
} else {
// big endian
for(j = 0; j < 4; j++) {
u.i = in[j];
printf("%02x%02x%02x%02x", u.c[3], u.c[2], u.c[1], u.c[0]);
}
}
printf("\n");
return 0;
}
#define FF(b,c,d) ( d ^ (b & (c ^ d)) ) // ( (b & c) | (~b & d) )
#define FG(b,c,d) FF(d, b, c) // ( (b & d) | (c & ~d) )
#define FH(b,c,d) ( b ^ c ^ d )
#define FI(b,c,d) ( c ^ (b | ~d) )
#define ROLL(a,s) ( (a<<s) | (a>>(32-s)) )
#define OP(func, a,b,c,d, k,s,t) a+=func(b,c,d)+k+t; a=b+ROLL(a,s)
int md5_is_self(const unsigned int in[4])
{
unsigned int A = 0x67452301;
unsigned int B = 0xefcdab89;
unsigned int C = 0x98badcfe;
unsigned int D = 0x10325476;
OP(FF, A, B, C, D, in[0], 7, 0xd76aa478);
OP(FF, D, A, B, C, in[1], 12, 0xe8c7b756);
OP(FF, C, D, A, B, in[2], 17, 0x242070db);
OP(FF, B, C, D, A, in[3], 22, 0xc1bdceee);
OP(FF, A, B, C, D, 0x80, 7, 0xf57c0faf);
OP(FF, D, A, B, C, 0, 12, 0x4787c62a);
OP(FF, C, D, A, B, 0, 17, 0xa8304613);
OP(FF, B, C, D, A, 0, 22, 0xfd469501);
OP(FF, A, B, C, D, 0, 7, 0x698098d8);
OP(FF, D, A, B, C, 0, 12, 0x8b44f7af);
OP(FF, C, D, A, B, 0, 17, 0xffff5bb1);
OP(FF, B, C, D, A, 0, 22, 0x895cd7be);
OP(FF, A, B, C, D, 0, 7, 0x6b901122);
OP(FF, D, A, B, C, 0, 12, 0xfd987193);
OP(FF, C, D, A, B, 0x80, 17, 0xa679438e);
OP(FF, B, C, D, A, 0, 22, 0x49b40821);
OP(FG, A, B, C, D, in[1], 5, 0xf61e2562);
OP(FG, D, A, B, C, 0, 9, 0xc040b340);
OP(FG, C, D, A, B, 0, 14, 0x265e5a51);
OP(FG, B, C, D, A, in[0], 20, 0xe9b6c7aa);
OP(FG, A, B, C, D, 0, 5, 0xd62f105d);
OP(FG, D, A, B, C, 0, 9, 0x02441453);
OP(FG, C, D, A, B, 0, 14, 0xd8a1e681);
OP(FG, B, C, D, A, 0x80, 20, 0xe7d3fbc8);
OP(FG, A, B, C, D, 0, 5, 0x21e1cde6);
OP(FG, D, A, B, C, 0x80, 9, 0xc33707d6);
OP(FG, C, D, A, B, in[3], 14, 0xf4d50d87);
OP(FG, B, C, D, A, 0, 20, 0x455a14ed);
OP(FG, A, B, C, D, 0, 5, 0xa9e3e905);
OP(FG, D, A, B, C, in[2], 9, 0xfcefa3f8);
OP(FG, C, D, A, B, 0, 14, 0x676f02d9);
OP(FG, B, C, D, A, 0, 20, 0x8d2a4c8a);
OP(FH, A, B, C, D, 0, 4, 0xfffa3942);
OP(FH, D, A, B, C, 0, 11, 0x8771f681);
OP(FH, C, D, A, B, 0, 16, 0x6d9d6122);
OP(FH, B, C, D, A, 0x80, 23, 0xfde5380c);
OP(FH, A, B, C, D, in[1], 4, 0xa4beea44);
OP(FH, D, A, B, C, 0x80, 11, 0x4bdecfa9);
OP(FH, C, D, A, B, 0, 16, 0xf6bb4b60);
OP(FH, B, C, D, A, 0, 23, 0xbebfbc70);
OP(FH, A, B, C, D, 0, 4, 0x289b7ec6);
OP(FH, D, A, B, C, in[0], 11, 0xeaa127fa);
OP(FH, C, D, A, B, in[3], 16, 0xd4ef3085);
OP(FH, B, C, D, A, 0, 23, 0x04881d05);
OP(FH, A, B, C, D, 0, 4, 0xd9d4d039);
OP(FH, D, A, B, C, 0, 11, 0xe6db99e5);
OP(FH, C, D, A, B, 0, 16, 0x1fa27cf8);
OP(FH, B, C, D, A, in[2], 23, 0xc4ac5665);
OP(FI, A, B, C, D, in[0], 6, 0xf4292244);
OP(FI, D, A, B, C, 0, 10, 0x432aff97);
OP(FI, C, D, A, B, 0x80, 15, 0xab9423a7);
OP(FI, B, C, D, A, 0, 21, 0xfc93a039);
OP(FI, A, B, C, D, 0, 6, 0x655b59c3);
OP(FI, D, A, B, C, in[3], 10, 0x8f0ccc92);
OP(FI, C, D, A, B, 0, 15, 0xffeff47d);
OP(FI, B, C, D, A, in[1], 21, 0x85845dd1);
OP(FI, A, B, C, D, 0, 6, 0x6fa87e4f);
OP(FI, D, A, B, C, 0, 10, 0xfe2ce6e0);
OP(FI, C, D, A, B, 0, 15, 0xa3014314);
OP(FI, B, C, D, A, 0, 21, 0x4e0811a1);
OP(FI, A, B, C, D, 0x80, 6, 0xf7537e82);
OP(FI, D, A, B, C, 0, 10, 0xbd3af235);
OP(FI, C, D, A, B, in[2], 15, 0x2ad7d2bb);
OP(FI, B, C, D, A, 0, 21, 0xeb86d391);
return A+0x67452301==in[0] && B+0xefcdab89==in[1] && C+0x98badcfe==in[2] && D+0x10325476==in[3];
}
int main(int argc, char * argv[])
{
// example:
unsigned int in[4] = { 0x5643237f, 0x1245e6a0, 0xd3e6aa01, 0x7f431234 };
while(in[3]++) {
if(md5_is_self(in)) {
print_md5(in);
return 0;
}
}
return 1;
}
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原文地址：http://my.oschina.net/2bit/blog/512670
