源代码 ：
#include#include #include #include unsigned char submit[6];void play(){ int i; printf("Submit your 6 lotto bytes : "); fflush(stdout); int r; r = read(0, submit, 6); printf("Lotto Start!\n"); //sleep(1); // generate lotto numbers int fd = open("/dev/urandom", O_RDONLY); if(fd==-1){ printf("error. tell admin\n"); exit(-1); } unsigned char lotto[6]; if(read(fd, lotto, 6) != 6){ printf("error2. tell admin\n"); exit(-1); } for(i=0; i<6; i++){ lotto[i] = (lotto[i] % 45) + 1; // 1 ~ 45 } close(fd); // calculate lotto score int match = 0, j = 0; for(i=0; i<6; i++){ for(j=0; j<6; j++){ if(lotto[i] == submit[j]){ match++; } } } // win! if(match == 6){ system("/bin/cat flag"); } else{ printf("bad luck...\n"); }}void help(){ printf("- nLotto Rule -\n"); printf("nlotto is consisted with 6 random natural numbers less than 46\n"); printf("your goal is to match lotto numbers as many as you can\n"); printf("if you win lottery for *1st place*, you will get reward\n"); printf("for more details, follow the link below\n"); printf("http://www.nlotto.co.kr/counsel.do?method=playerGuide#buying_guide01\n\n"); printf("mathematical chance to win this game is known to be 1/8145060.\n");}int main(int argc, char* argv[]){ // menu unsigned int menu; while(1){ printf("- Select Menu -\n"); printf("1. Play Lotto\n"); printf("2. Help\n"); printf("3. Exit\n"); scanf("%d", &menu); switch(menu){ case 1: play(); break; case 2: help(); break; case 3: printf("bye\n"); return 0; default: printf("invalid menu\n"); break; } } return 0;}
关键程序 ：
1 int match = 0, j = 0; 2 for(i=0; i<6; i++){ 3 for(j=0; j<6; j++){ 4 if(lotto[i] == submit[j]){ 5 match++; 6 } 7 } 8 } 9 10 // win!11 if(match == 6){12 system("/bin/cat flag");13 } 题中让输入的Lotto在1-45范围之内，并且当lotto等于submit的时候，match加1，当match回到6的时候得到flag。而lotto是本地生成的，那么看一下它是怎么生成的：
1 for(i=0; i<6; i++){2 lotto[i] = (lotto[i] % 45) + 1; // 1 ~ 453 }4 close(fd); 思路是在1-45范围内随机生成。
看一下assic表：
真正符号输入是从33开始的，那我们在这个范围内选择字符输入。
如图选择一个字符一直输入，总能找到相等的字符，达到6个得到flag:
sorry mom... I FORGOT to check duplicate numbers... :(