#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>

int main(int argc, char* argv[]){
    char fname[128];
    unsigned long long otp[2];

    if(argc!=2){
        printf("usage : ./otp [passcode]\n");
        return 0;
    }

    int fd = open("/dev/urandom", O_RDONLY);
    if(fd==-1) exit(-1);

    if(read(fd, otp, 16)!=16) exit(-1);
    close(fd);

    sprintf(fname, "/tmp/%llu", otp[0]);
    FILE* fp = fopen(fname, "w");
    if(fp==NULL){ exit(-1); }
    fwrite(&otp[1], 8, 1, fp);
    fclose(fp);

    printf("OTP generated.\n");

    unsigned long long passcode=0;
    FILE* fp2 = fopen(fname, "r");
    if(fp2==NULL){ exit(-1); }
    fread(&passcode, 8, 1, fp2);
    fclose(fp2);

    if(strtoul(argv[1], 0, 16) == passcode){
        printf("Congratz!\n");
        system("/bin/cat flag");
    }
    else{
        printf("OTP mismatch\n");
    }

    unlink(fname);
    return 0;
}