rev/vault_door_3

rev/vault_door_3/VaultDoor3.java

@@ -0,0 +1,44 @@
+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_3lpm11g54e_u_4_m4r042");
+    }
+}

rev/vault_door_3/solve.py

@@ -0,0 +1,63 @@
+#!/usr/bin/env python3
+
+# 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_3lpm11g54e_u_4_m4r042");
+# }
+
+def encode(xs: list):
+    assert len(xs) == 32
+    result = [None] * 32
+
+    for i in range(0, 8):
+        result[i] = xs[i]
+
+    for i in range(8, 16):
+        result[i] = xs[23 - i]
+
+    for i in range(16, 32, 2):
+        result[i] = xs[46 - i]
+
+    for i in range(31, 16, -2):
+        result[i] = xs[i]
+
+    return result
+
+def decode(xs: list):
+    assert len(xs) == 32
+    indices = list(range(len(xs)))
+    shuffled = encode(indices)
+
+    ordered = [None] * len(xs)
+    for i, idx in enumerate(shuffled):
+        ordered[idx] = xs[i]
+
+    return ordered
+
+
+assert encode(decode( list(range(32)) )) == list(range(32))
+
+def main():
+    output = "jU5t_a_sna_3lpm11g54e_u_4_m4r042"
+    print("picoCTF{" + ''.join(decode(list(output))) + "}")
+
+if __name__ == '__main__':
+    main()
+