package pwd;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import java.math.BigInteger;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.spec.InvalidKeySpecException;
public class PBKDF2 {
  public static void main(String[] args) throws NoSuchAlgorithmException, InvalidKeySpecException {
    String originalPassword = "password";
    String encryptedPassword = generateStorngPasswordHash(originalPassword);
    System.out.println(encryptedPassword);
    String originalPassword2 = "123456";
    System.out.println("origin pwd: " + originalPassword + "  ; result > " + checkPW("userId", originalPassword, encryptedPassword));
    System.out.println("origin pwd: " + originalPassword2 + "  ; result > " + checkPW("userId", originalPassword2, encryptedPassword));
    //Output:
    //1000:14cc179bf6c2b8acb3daaca45b9d2f75:2e81f5220266cdddd13f98c458ae6388abe563a63244d0e4c8d0738a2bfa0fd2bfcfcbffab9cf2ec596c64d3f1db7468b95785f5adb21ed5580972fd87f2e854
    //origin pwd: password  ; result > true
    //origin pwd: 123456  ; result > false
  }
  public static Boolean checkPW(String userId, String originalPassword, String encryptedPassword)  throws NoSuchAlgorithmException, InvalidKeySpecException {
    return validatePassword(originalPassword, encryptedPassword);
  }
  private static boolean validatePassword(String originalPassword, String storedPassword) throws NoSuchAlgorithmException, InvalidKeySpecException {
    String[] parts = storedPassword.split(":");
    int iterations = Integer.parseInt(parts[0]);
    byte[] salt = fromHex(parts[1]);
    byte[] hash = fromHex(parts[2]);
    PBEKeySpec spec = new PBEKeySpec(originalPassword.toCharArray(), salt, iterations, hash.length * 8);
    SecretKeyFactory skf = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
    byte[] testHash = skf.generateSecret(spec).getEncoded();
    int diff = hash.length ^ testHash.length;
    for(int i = 0; i < hash.length && i < testHash.length; i++) {
      diff |= hash[i] ^ testHash[i];
    }
    return diff == 0;
  }
  private static byte[] fromHex(String hex) throws NoSuchAlgorithmException {
    byte[] bytes = new byte[hex.length() / 2];
    for(int i = 0; i<bytes.length ;i++) {
      bytes[i] = (byte)Integer.parseInt(hex.substring(2 * i, 2 * i + 2), 16);
    }
    return bytes;
  }
  private static String generateStorngPasswordHash(String password) throws NoSuchAlgorithmException, InvalidKeySpecException {
    int iterations = 1000;
    char[] chars = password.toCharArray();
    byte[] salt = getSalt();
    PBEKeySpec spec = new PBEKeySpec(chars, salt, iterations, 64*8);
    SecretKeyFactory skf = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
    byte[] hash = skf.generateSecret(spec).getEncoded();
    return iterations + ":" + toHex(salt) + ":" + toHex(hash);
  }
  private static byte[] getSalt() throws NoSuchAlgorithmException {
    SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
    byte[] salt = new byte[16];
    sr.nextBytes(salt);
    return salt;
  }
  private static String toHex(byte[] array) throws NoSuchAlgorithmException {
    BigInteger bi = new BigInteger(1, array);
    String hex = bi.toString(16);
    int paddingLength = (array.length * 2) - hex.length();
    if (paddingLength > 0) {
      return String.format("%0" + paddingLength + "d", 0) + hex;
    }
    return hex;
  }
}