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vault-door-7/VaultDoor7.java

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+import java.util.*;
+import javax.crypto.Cipher;
+import javax.crypto.spec.SecretKeySpec;
+import java.security.*;
+
+class VaultDoor7 {
+    public static void main(String args[]) {
+        VaultDoor7 vaultDoor = new VaultDoor7();
+        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!");
+        }
+    }
+
+    // Each character can be represented as a byte value using its
+    // ASCII encoding. Each byte contains 8 bits, and an int contains
+    // 32 bits, so we can "pack" 4 bytes into a single int. Here's an
+    // example: if the hex string is "01ab", then those can be
+    // represented as the bytes {0x30, 0x31, 0x61, 0x62}. When those
+    // bytes are represented as binary, they are:
+    //
+    // 0x30: 00110000
+    // 0x31: 00110001
+    // 0x61: 01100001
+    // 0x62: 01100010
+    //
+    // If we put those 4 binary numbers end to end, we end up with 32
+    // bits that can be interpreted as an int.
+    //
+    // 00110000001100010110000101100010 -> 808542562
+    //
+    // Since 4 chars can be represented as 1 int, the 32 character password can
+    // be represented as an array of 8 ints.
+    //
+    // - Minion #7816
+    public int[] passwordToIntArray(String hex) {
+        int[] x = new int[8];
+        byte[] hexBytes = hex.getBytes();
+        for (int i=0; i<8; i++) {
+            x[i] = hexBytes[i*4]   << 24
+                 | hexBytes[i*4+1] << 16
+                 | hexBytes[i*4+2] << 8
+                 | hexBytes[i*4+3];
+        }
+        return x;
+    }
+
+    public boolean checkPassword(String password) {
+        if (password.length() != 32) {
+            return false;
+        }
+        int[] x = passwordToIntArray(password);
+        return x[0] == 1096770097
+            && x[1] == 1952395366
+            && x[2] == 1600270708
+            && x[3] == 1601398833
+            && x[4] == 1716808014
+            && x[5] == 1734291511
+            && x[6] == 960049251
+            && x[7] == 1681089078;
+    }
+}