MinecraftPasswordRetrieval.java

import java.io.*;
import java.util.Random;
import javax.crypto.*;
import javax.crypto.spec.*;

public class MinecraftPasswordRetrieval {
    public static final String ENCRYPTION_TYPE       = "PBEWithMD5AndDES";
    public static final int    ENCRYPTION_ITERATIONS = 5;
    public static final String ENCRYPTION_KEY        = "passwordfile";
    public static final long   SALT_SEED   = 43287234L;
    public static final int    SALT_LENGTH = 8;

    public static void main(String[] args) throws Exception {
        File passFile = new File(getMinecraftDir(), "lastlogin");
        DataInputStream dis = new DataInputStream(new CipherInputStream(new FileInputStream(passFile), getCipher()));
        System.out.println("Username: " + dis.readUTF());
        System.out.println("Password: " + dis.readUTF());
        dis.close();
    }

    public static File getMinecraftDir() {
        File home = new File(System.getProperty("user.home"));
        switch (OS.getOS()) {
            case WINDOWS: return new File(System.getenv("APPDATA"), ".minecraft");
            case MACOSX:  return new File(home, "Library/Application Support/minecraft");
            case LINUX:   return new File(home, ".minecraft");
        }
        throw new RuntimeException("The Compiler is too stupid to realize that this line is dead code.");
    }

    public static Cipher getCipher() throws Exception {
        SecretKey pbeKey = SecretKeyFactory.getInstance(ENCRYPTION_TYPE).generateSecret(new PBEKeySpec(ENCRYPTION_KEY.toCharArray()));
        PBEParameterSpec pbeParamSpec = new PBEParameterSpec(getSalt(), ENCRYPTION_ITERATIONS);
        Cipher cipher = Cipher.getInstance(ENCRYPTION_TYPE);
        cipher.init(Cipher.DECRYPT_MODE, pbeKey, pbeParamSpec);
        return cipher;
    }

    public static byte[] getSalt() {
        Random random = new Random(SALT_SEED);
        byte[] salt = new byte[SALT_LENGTH];
        random.nextBytes(salt);
        return salt;
    }

    public static enum OS { // http://java.net/projects/swingx/sources/svn/content/trunk/swingx-core/src/main/java/org/jdesktop/swingx/util/Utilities.java
        WINDOWS, LINUX, MACOSX;
        public static OS getOS() {
            String osName = System.getProperty("os.name");
            if (osName.startsWith("Windows"))
                return WINDOWS;
            else if (osName.equals("Mac OS X"))
                return MACOSX;
            return LINUX; // Linux, BSD, Solaris, …
        }
    }
}