vault-door-3
This vault uses for-loops and byte arrays. The source code for this vault is here: VaultDoor3.java
Download the Java file.
The password check rearranges 32 input characters before comparing them with a fixed string. To reverse it, map each character of that fixed string back to the original password index used by the loops: positions 0–7 stay unchanged, 8–15 are reversed, even positions 16–30 use 46-i, and odd positions 17–31 stay unchanged. This recovers the password body; wrap it in picoCTF{...}.
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import java.util.*;
class VaultDoor3 {
public static void main(String args[]) {
VaultDoor3 vaultDoor = new VaultDoor3();
Scanner scanner = new Scanner(System.in);
System.out.print("Enter vault password: ");
String userInput = scanner.next();
String input = userInput.substring("picoCTF{".length(),userInput.length()-1);
if (vaultDoor.checkPassword(input)) {
System.out.println("Access granted.");
} else {
System.out.println("Access denied!");
}
}
// Our security monitoring team has noticed some intrusions on some of the
// less secure doors. Dr. Evil has asked me specifically to build a stronger
// vault door to protect his Doomsday plans. I just *know* this door will
// keep all of those nosy agents out of our business. Mwa ha!
//
// -Minion #2671
public boolean checkPassword(String password) {
if (password.length() != 32) {
return false;
}
char[] buffer = new char[32];
int i;
for (i=0; i<8; i++) {
buffer[i] = password.charAt(i);
}
for (; i<16; i++) {
buffer[i] = password.charAt(23-i);
}
for (; i<32; i+=2) {
buffer[i] = password.charAt(46-i);
}
for (i=31; i>=17; i-=2) {
buffer[i] = password.charAt(i);
}
String s = new String(buffer);
return s.equals("jU5t_a_sna_3lpm1cg04e_u_4_m6rb42");
}
}
This post is licensed under CC BY 4.0 by the author.