Problem: Apparently Dr. Evil’s minions knew that our agency was making copies of their source code, because they intentionally sabotaged this source code in order to make it harder for our agents to analyze and crack into! The result is a quite mess, but I trust that my best special agent will find a way to solve it. The source code for this vault is here: VaultDoor8.java

File: THE_FILE

Solution:

Beautify the file with an online tool to make it more readable.

// These pesky special agents keep reverse engineering our source code and then
// breaking into our secret vaults. THIS will teach those sneaky sneaks a
// lesson.
//
// -Minion #0891
import java.util.*;
import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import java.security.*;
class VaultDoor8 {
    public static void main(String args[]) {
        Scanner b = new Scanner(System.in);
        System.out.print("Enter vault password: ");
        String c = b.next();
        String f = c.substring(8, c.length() - 1);
        VaultDoor8 a = new VaultDoor8();
        if (a.checkPassword(f)) {
            System.out.println("Access granted.");
        } else {
            System.out.println("Access denied!");
        }
    }
    public char[] scramble(String password) { /* Scramble a password by transposing pairs of bits. */
        char[] a = password.toCharArray();
        for (int b = 0; b < a.length; b++) {
            char c = a[b];
            c = switchBits(c, 1, 2);
            c = switchBits(c, 0, 3); /* c = switchBits(c,14,3); c = switchBits(c, 2, 0); */
            c = switchBits(c, 5, 6);
            c = switchBits(c, 4, 7);
            c = switchBits(c, 0, 1); /* d = switchBits(d, 4, 5); e = switchBits(e, 5, 6); */
            c = switchBits(c, 3, 4);
            c = switchBits(c, 2, 5);
            c = switchBits(c, 6, 7);
            a[b] = c;
        }
        return a;
    }
    public char switchBits(char c, int p1, int p2) {
        /* Move the bit in position p1 to position p2, and move the bit
        that was in position p2 to position p1. Precondition: p1 < p2 */
        char mask1 = (char)(1 << p1);
        char mask2 = (char)(1 << p2); /* char mask3 = (char)(1<<p1<<p2); mask1++; mask1--; */
        char bit1 = (char)(c & mask1);
        char bit2 = (char)(c & mask2);
        /* System.out.println("bit1 " + Integer.toBinaryString(bit1));
System.out.println("bit2 " + Integer.toBinaryString(bit2)); */
        char rest = (char)(c & ~(mask1 | mask2));
        char shift = (char)(p2 - p1);
        char result = (char)((bit1 << shift) | (bit2 >> shift) | rest);
        return result;
    }
    public boolean checkPassword(String password) {
        char[] scrambled = scramble(password);
        char[] expected = {
            0xF4,
            0xC0,
            0x97,
            0xF0,
            0x77,
            0x97,
            0xC0,
            0xE4,
            0xF0,
            0x77,
            0xA4,
            0xD0,
            0xC5,
            0x77,
            0xF4,
            0x86,
            0xD0,
            0xA5,
            0x45,
            0x96,
            0x27,
            0xB5,
            0x77,
            0xA4,
            0xF1,
            0x94,
            0xC1,
            0xC0,
            0xE1,
            0xC1,
            0xD1,
            0x85
        };
        return Arrays.equals(scrambled, expected);
    }
}

Main.java Switch the scramble order to un scramble the flag.

// These pesky special agents keep reverse engineering our source code and then
// breaking into our secret vaults. THIS will teach those sneaky sneaks a
// lesson.
//
// -Minion #0891
import java.util.*;
import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import java.security.*;
class Main {
	public static void main(String args[]) {
		char[] expected = {
			0xF4, 0xC0, 0x97, 0xF0, 0x77, 0x97, 0xC0, 0xE4, 0xF0, 
			0x77, 0xA4, 0xD0, 0xC5, 0x77, 0xF4, 0x86, 0xD0, 0xA5, 
			0x45, 0x96, 0x27, 0xB5, 0x77, 0xA4, 0xF1, 0x94, 0xC1, 
			0xC0, 0xE1, 0xC1, 0xD1, 0x85
		};
		System.out.println(String.valueOf(unscrable(String.valueOf(expected))));
	}
	public static char[] unscrable(String password) {
		char[] a = password.toCharArray();
		for (int b = 0; b < a.length; b++) {
		// To unscrable do everything backwards
			char c = a[b];
			c = switchBits(c, 6, 7);
			c = switchBits(c, 2, 5);
			c = switchBits(c, 3, 4);
			c = switchBits(c, 0, 1); /* d = switchBits(d, 4, 5); e = switchBits(e, 5, 6); */
			c = switchBits(c, 4, 7);
			c = switchBits(c, 5, 6);
			c = switchBits(c, 0, 3); /* c = switchBits(c,14,3); c = switchBits(c, 2, 0); */
			c = switchBits(c, 1, 2);
			a[b] = c;
		}
		return a;
	}
	public static char switchBits(char c, int p1, int p2) {
		/* Move the bit in position p1 to position p2, and move the bit
		that was in position p2 to position p1. Precondition: p1 < p2 */
		char mask1 = (char)(1 << p1);
		char mask2 = (char)(1 << p2); /* char mask3 = (char)(1<<p1<<p2); mask1++; mask1--; */
		char bit1 = (char)(c & mask1);
		char bit2 = (char)(c & mask2);
		/* System.out.println("bit1 " + Integer.toBinaryString(bit1));
System.out.println("bit2 " + Integer.toBinaryString(bit2)); */
		char rest = (char)(c & ~(mask1 | mask2));
		char shift = (char)(p2 - p1);
		char result = (char)((bit1 << shift) | (bit2 >> shift) | rest);
		return result;
	}
}

Flag: picoCTF{s0m3_m0r3_b1t_sh1fTiNg_b7a40645d}