| 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] == 1734304867 | |
| && x[6] == 942695730 | |
| && x[7] == 942748212; | |
| } | |
| } | |