这道题目很有挑战性,简单讲一下,欢迎论坛兄弟交流。
下载程序,peid检查发现是ASProtect 1.2x - 1.3x [Registered] -> Alexey Solodovnikov,加密壳直接在论坛找脚本脱掉,再次检查发现是Microsoft Visual Studio .NET 2005 -- 2008 -> Microsoft Corporation 。注意程序会用函数kernel32.GetVersionExW检查你的操作系统,xp的话会直接结束,win7则正常出现flag输入窗口。
大致原理:内存中有一块加密数据,解密后是bmp像素信息,从图像信息得到一串数字;而我们输入的字符串经过某种加密也得到一串数字,如果相同的话,输入的字符串就是flag.
图像的解密算法:
#include <stdio.h>
#include <stdlib.h>
#define SIZE 0x1800
int main(int argc, char *argv[])
{
FILE * fp;
unsigned char buf[SIZE*4];
fp = fopen("enc.dat", "rb");
fread(buf, sizeof(unsigned char), 0x6000,fp);
fclose(fp);
unsigned int i = 0;
unsigned int n = 0;
unsigned int m;
do
{
m = (*(unsigned int *)(buf + 4 *i + 1)) ^ n ^ (0x1800 - i) ;
n = n + (*(unsigned int *)(buf + 4 *i + 1));
*(unsigned int *)(buf + 4 *i + 1) = (m >> 17)+ (m << 15);
i++;
}
while ( i < (unsigned int)(0x1800 - 1) );
fp = fopen("enc.dat", "wb");
fwrite( buf, sizeof( unsigned char ), 0x6000,fp);
fclose(fp);
system("PAUSE");
}
输入字符串的加密算法:
#include <stdio.h>
#include <stdlib.h>
#define byte unsigned char
byte buf[16]={0};
unsigned char data[16] = {
0xCF, 0xE3, 0x04, 0x6F, 0xC2, 0x1C, 0x39, 0x6F, 0xDC, 0xAF, 0xC8, 0x43, 0x6A, 0xAB, 0xEB, 0x2C
};
static unsigned char index[16] = {
0x00, 0x04, 0x08, 0x0C, 0x01, 0x05, 0x09, 0x0D, 0x02, 0x06, 0x0A, 0x0E, 0x03, 0x07, 0x0B, 0x0F
};
unsigned char idx_401230[16] = {
0x00, 0x01, 0x02, 0x03, 0x05, 0x06, 0x07, 0x04, 0x0A, 0x0B, 0x08, 0x09, 0x0F, 0x0C, 0x0D, 0x0E
};
static unsigned char key[0xB0] = {
0x2C, 0xC2, 0xDC, 0x6A, 0xE3, 0xAB, 0xAF, 0x1C, 0x04, 0x6F, 0xC8, 0xEB, 0x39, 0x6F, 0x43, 0xCF,
0xB1, 0x73, 0xAF, 0xC5, 0x0A, 0xA1, 0x0E, 0x12, 0x8E, 0xE1, 0x29, 0xC2, 0x3B, 0x54, 0x17, 0xD8,
0x7A, 0x09, 0xA6, 0x63, 0x2F, 0x8E, 0x80, 0x92, 0xEF, 0x0E, 0x27, 0xE5, 0x9D, 0xC9, 0xDE, 0x06,
0x31, 0x38, 0x9E, 0xFD, 0xF6, 0x78, 0xF8, 0x6A, 0x80, 0x8E, 0xA9, 0x4C, 0x66, 0xAF, 0x71, 0x77,
0x3B, 0x03, 0x9D, 0x60, 0xDF, 0xA7, 0x5F, 0x35, 0x75, 0xFB, 0x52, 0x1E, 0x32, 0x9D, 0xEC, 0x9B,
0xBD, 0xBE, 0x23, 0x43, 0xAD, 0x0A, 0x55, 0x60, 0x61, 0x9A, 0xC8, 0xD6, 0xE2, 0x7F, 0x93, 0x08,
0x4D, 0xF3, 0xD0, 0x93, 0x5B, 0x51, 0x04, 0x64, 0x51, 0xCB, 0x03, 0xD5, 0xF8, 0x87, 0x14, 0x1C,
0x4E, 0xBD, 0x6D, 0xFE, 0x58, 0x09, 0x0D, 0x69, 0xCD, 0x06, 0x05, 0xD0, 0x24, 0xA3, 0xB7, 0xAB,
0x37, 0x8A, 0xE7, 0x19, 0x28, 0x21, 0x2C, 0x45, 0xAF, 0xA9, 0xAC, 0x7C, 0x9F, 0x3C, 0x8B, 0x20,
0x42, 0xC8, 0x2F, 0x36, 0x38, 0x19, 0x35, 0x70, 0x18, 0xB1, 0x1D, 0x61, 0x4B, 0x77, 0xFC, 0xDC,
0x25, 0xED, 0xC2, 0xF4, 0xD7, 0xCE, 0xFB, 0x8B, 0x9E, 0x2F, 0x32, 0x53, 0x4E, 0x39, 0xC5, 0x19
};
unsigned char substitute[0x100] = {
0x52, 0x09, 0x6A, 0xD5, 0x30, 0x36, 0xA5, 0x38, 0xBF, 0x40, 0xA3, 0x9E, 0x81, 0xF3, 0xD7, 0xFB,
0x7C, 0xE3, 0x39, 0x82, 0x9B, 0x2F, 0xFF, 0x87, 0x34, 0x8E, 0x43, 0x44, 0xC4, 0xDE, 0xE9, 0xCB,
0x54, 0x7B, 0x94, 0x32, 0xA6, 0xC2, 0x23, 0x3D, 0xEE, 0x4C, 0x95, 0x0B, 0x42, 0xFA, 0xC3, 0x4E,
0x08, 0x2E, 0xA1, 0x66, 0x28, 0xD9, 0x24, 0xB2, 0x76, 0x5B, 0xA2, 0x49, 0x6D, 0x8B, 0xD1, 0x25,
0x72, 0xF8, 0xF6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xD4, 0xA4, 0x5C, 0xCC, 0x5D, 0x65, 0xB6, 0x92,
0x6C, 0x70, 0x48, 0x50, 0xFD, 0xED, 0xB9, 0xDA, 0x5E, 0x15, 0x46, 0x57, 0xA7, 0x8D, 0x9D, 0x84,
0x90, 0xD8, 0xAB, 0x00, 0x8C, 0xBC, 0xD3, 0x0A, 0xF7, 0xE4, 0x58, 0x05, 0xB8, 0xB3, 0x45, 0x06,
0xD0, 0x2C, 0x1E, 0x8F, 0xCA, 0x3F, 0x0F, 0x02, 0xC1, 0xAF, 0xBD, 0x03, 0x01, 0x13, 0x8A, 0x6B,
0x3A, 0x91, 0x11, 0x41, 0x4F, 0x67, 0xDC, 0xEA, 0x97, 0xF2, 0xCF, 0xCE, 0xF0, 0xB4, 0xE6, 0x73,
0x96, 0xAC, 0x74, 0x22, 0xE7, 0xAD, 0x35, 0x85, 0xE2, 0xF9, 0x37, 0xE8, 0x1C, 0x75, 0xDF, 0x6E,
0x47, 0xF1, 0x1A, 0x71, 0x1D, 0x29, 0xC5, 0x89, 0x6F, 0xB7, 0x62, 0x0E, 0xAA, 0x18, 0xBE, 0x1B,
0xFC, 0x56, 0x3E, 0x4B, 0xC6, 0xD2, 0x79, 0x20, 0x9A, 0xDB, 0xC0, 0xFE, 0x78, 0xCD, 0x5A, 0xF4,
0x1F, 0xDD, 0xA8, 0x33, 0x88, 0x07, 0xC7, 0x31, 0xB1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xEC, 0x5F,
0x60, 0x51, 0x7F, 0xA9, 0x19, 0xB5, 0x4A, 0x0D, 0x2D, 0xE5, 0x7A, 0x9F, 0x93, 0xC9, 0x9C, 0xEF,
0xA0, 0xE0, 0x3B, 0x4D, 0xAE, 0x2A, 0xF5, 0xB0, 0xC8, 0xEB, 0xBB, 0x3C, 0x83, 0x53, 0x99, 0x61,
0x17, 0x2B, 0x04, 0x7E, 0xBA, 0x77, 0xD6, 0x26, 0xE1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0C, 0x7D
};
int main(int argc, char *argv[])
{
byte tmp[16]={0};
int i,j;
for(i=0;i<16;i++) {
printf("%02x ",data[i]);
}
printf("\n");
for(i=0;i<16;i++) tmp[index[i]]=~data[i];
for(i=0;i<16;i++) buf[i]=tmp[i];
j=10;
do {
for(i=0;i<16;i++) { buf[i]= buf[i] ^ key[16*j +i]; }
if (j!=10) { sub_4012D0();sub_4012D0();sub_4012D0(); }
sub_401230();
sub_401140();
j--;
} while(j>0);
j=0;
for(i=0;i<16;i++) buf[i]=buf[i] ^ key[16*j +i];
for(i=0;i<4;i++) {
tmp[i]=buf[4*i];
tmp[i+4]=buf[4*i+1];
tmp[i+8]=buf[4*i+2];
tmp[i+0xC]=buf[4*i+3];
}
for(i=0;i<16;i++) buf[i]=tmp[i];
show_buf(); //
system("PAUSE");
}
void sub_4012D0()
{
char b1,b2,b3,b4,tt;
int i;
char tmp[16]={0};
for(i=0;i<16;i++) tmp[i]=buf[i];
for(i=0;i<16;i++)
{
b1=tmp[i]; b2=tmp[(i+4)%16]; b3=tmp[(i+8)%16]; b4=tmp[(i+12)%16];
tt=b1;
b1=2*b1;
if(tt<0) { b1^=0x1B; }
tt=b2;
b2=2*b2;
if(tt<0) { b2^=0x1B; }
b2=tt ^ b2;
buf[i]=b1 ^ b2 ^ b3 ^ b4;
}
}
void sub_401140()
{
int i;
for(i=0;i<16;i++) {
buf[i]=substitute[buf[i]];
}
}
void sub_401230()
{
byte tmp[16]={0};
int i;
for(i=0;i<16;i++) tmp[idx_401230[i]]=buf[i];
for(i=0;i<16;i++) buf[i]=tmp[i];
}
void show_buf(){
int i;
for(i=0;i<16;i++) {
printf("%02x ",buf[i]);
}
printf("\n");
}
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