import java.security.SecureRandom;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.SecretKeySpec;
import javax.crypto.KeyGenerator;
import javax.crypto.Mac;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.spec.InvalidKeySpecException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Formatter;
import java.util.Scanner;

/*
 * PBKDF2 salted password hashing.
 * Author: havoc AT defuse.ca
 * www: http://crackstation.net/hashing-security.htm
 */
public class TokenLogin {
    public static final String PBKDF2_ALGORITHM = "PBKDF2WithHmacSHA1";

    // The following constants may be changed without breaking existing hashes.
    public static final int SALT_BYTES = 20;
    public static final int HASH_BYTES = 20;
    public static final int PBKDF2_ITERATIONS = 1000;

    public static final int ITERATION_INDEX = 0;
    public static final int SALT_INDEX = 1;
    public static final int PBKDF2_INDEX = 2;

    /**
     * Returns a salted PBKDF2 hash of the password.
     *
     * @param   password    the password to hash
     * @return              a salted PBKDF2 hash of the password
     */
    public static String createHash(String password)
        throws NoSuchAlgorithmException, InvalidKeySpecException
    {
        return createHash(password.toCharArray());
    }

    /**
     * Returns a salted PBKDF2 hash of the password.
     *
     * @param   password    the password to hash
     * @return              a salted PBKDF2 hash of the password
     */
    public static String createHash(char[] password)
        throws NoSuchAlgorithmException, InvalidKeySpecException
    {
        // Generate a random salt
        SecureRandom random = new SecureRandom();
        byte[] salt = new byte[SALT_BYTES];
        random.nextBytes(salt);

        // Hash the password
        byte[] hash = pbkdf2(password, salt, PBKDF2_ITERATIONS, HASH_BYTES);
        // format iterations:salt:hash
        return PBKDF2_ITERATIONS + ":" + toHex(salt) + ":" +  toHex(hash);
    }

    /**
     * Validates a password using a hash.
     *
     * @param   password    the password to check
     * @param   goodHash    the hash of the valid password
     * @return              true if the password is correct, false if not
     */
    public static boolean validatePassword(String password, String goodHash)
        throws NoSuchAlgorithmException, InvalidKeySpecException
    {
        return validatePassword(password.toCharArray(), goodHash);
    }

    /**
     * Validates a password using a hash.
     *
     * @param   password    the password to check
     * @param   goodHash    the hash of the valid password
     * @return              true if the password is correct, false if not
     */
    public static boolean validatePassword(char[] password, String goodHash)
        throws NoSuchAlgorithmException, InvalidKeySpecException
    {
        // Decode the hash into its parameters
        String[] params = goodHash.split(":");
        int iterations = Integer.parseInt(params[ITERATION_INDEX]);
        byte[] salt = fromHex(params[SALT_INDEX]);
        byte[] hash = fromHex(params[PBKDF2_INDEX]);
        // Compute the hash of the provided password, using the same salt, 
        // iteration count, and hash length
        byte[] testHash = pbkdf2(password, salt, iterations, hash.length);
        // Compare the hashes in constant time. The password is correct if
        // both hashes match.
        return slowEquals(hash, testHash);        
    }

    /**
     * Compares two byte arrays in length-constant time. This comparison method
     * is used so that password hashes cannot be extracted from an on-line 
     * system using a timing attack and then attacked off-line.
     * 
     * @param   a       the first byte array
     * @param   b       the second byte array 
     * @return          true if both byte arrays are the same, false if not
     */
    private static boolean slowEquals(byte[] a, byte[] b)
    {
        int diff = a.length ^ b.length;
        for(int i = 0; i < a.length && i < b.length; i++)
            diff |= a[i] ^ b[i];
        return diff == 0;
    }

    /**
     *  Computes the PBKDF2 hash of a password.
     *
     * @param   password    the password to hash.
     * @param   salt        the salt
     * @param   iterations  the iteration count (slowness factor)
     * @param   bytes       the length of the hash to compute in bytes
     * @return              the PBDKF2 hash of the password
     */
    private static byte[] pbkdf2(char[] password, byte[] salt, int iterations, int bytes)
        throws NoSuchAlgorithmException, InvalidKeySpecException  {
        PBEKeySpec spec = new PBEKeySpec(password, salt, iterations, bytes * 8);
        SecretKeyFactory skf = SecretKeyFactory.getInstance(PBKDF2_ALGORITHM);
        return skf.generateSecret(spec).getEncoded();    
    }

    /**
     * Converts a string of hexadecimal characters into a byte array.
     *
     * @param   hex         the hex string
     * @return              the hex string decoded into a byte array
     */
    private static byte[] fromHex(String hex)
    {
        byte[] binary = new byte[hex.length() / 2];
        for(int i = 0; i < binary.length; i++)
        {
            binary[i] = (byte)Integer.parseInt(hex.substring(2*i, 2*i+2), 16);
        }
        return binary;
    }

    /**
     * Converts a byte array into a hexadecimal string.
     *
     * @param   array       the byte array to convert
     * @return              a length*2 character string encoding the byte array
     */
    private static String toHex(byte[] array)
    {
        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;
        else
            return hex;
    }
    
	public static String bytesToHex(byte[] bytes) {
	    StringBuilder sb = new StringBuilder(bytes.length * 2);
	 
	    @SuppressWarnings("resource")
		Formatter formatter = new Formatter(sb);
	    for (byte b : bytes) {
	        formatter.format("%02x", b);
	    }
	 
	    return sb.toString();
	}
	
	public static byte[] generateAutoLoginToken(byte[] secretToken, String time) throws NoSuchAlgorithmException {
		MessageDigest md = MessageDigest.getInstance("SHA1");
		md.update(secretToken);
		md.update(time.getBytes());
		byte[] autoLoginToken = md.digest();
		return autoLoginToken;
	}

	public static boolean verifyAutoLoginToken(Mac mac, byte[] publicToken, String time, byte[] autoLoginToken) throws NoSuchAlgorithmException {
        mac.update(publicToken);
        byte[] secretToken1 = mac.doFinal(); 
        System.out.println("비밀토큰: SecToken=HMAC(PubToken,K)");
        System.out.println("서버에서 복구된 비밀 토큰: "+bytesToHex(secretToken1));
		MessageDigest md = MessageDigest.getInstance("SHA1");
		md.update(secretToken1);
		md.update(time.getBytes());
		byte[] autoLoginToken1 = md.digest();
		System.out.println("자동로그인토큰: AutoLoginToken=H(SecToken,T)");
		System.out.println("서버에서 계산된 자동로그인 토큰: "+bytesToHex(autoLoginToken1));
		if(slowEquals(autoLoginToken, autoLoginToken1))
			return true;
		else 
			return false;
	}
	

    /**
     * Tests the basic functionality of the PasswordHash class
     *
     * @param   args        ignored
     */
    public static void main(String[] args)  {
    	
    	Scanner a = new Scanner(System.in);
    	
        try
        {
        	KeyGenerator kg = KeyGenerator.getInstance("AES"); 
			SecretKey key = kg.generateKey();
			SecretKeySpec keySpec = new SecretKeySpec(key.getEncoded(),"HmacSHA1");
			byte[] serverKey = key.getEncoded(); 
			System.out.println("안전한 자동 로그인 시스템 시뮬레이션");
			System.out.println();
			System.out.println("서버의 비밀키 (K) : "+bytesToHex(serverKey));
			System.out.println();
            			
            // Test password validation
            System.out.println("시뮬레이션 순서 ");
            System.out.println();
            System.out.println("1. 사용자 등록 (서버에 아이디, 패스워드 등록)");
            System.out.println("2. 사용자 로그인 (아이디, 패스워드로 서버에 로그인)");
            System.out.println("3. 서버가 사용자에게 토큰 발급 ");
            System.out.println("4. 토큰을 이용한 자동 로그인 ");
            System.out.println("5. 서버의 자동 로그인 검증 ");
            System.out.println();
            
            System.out.println("1. 사용자 등록 ");
            System.out.print("등록할 아이디를 입력하세요>> ");
            String id= a.next();
            System.out.print("등록할 패스워드를 입력하세요>> ");            
            String password = a.next();
            String hash = createHash(password);
            System.out.println("사용자가 입력한 아이디(ID): "+id);
            System.out.println("사용자가 입력한 패스워드(Pass): "+password);
            System.out.println("서버에 저장된 패스워드 해쉬(PassHash): "+hash); 
            if(validatePassword(password, hash)) {
            	System.out.println("패스워드 유효성 검증: valid");
                //System.out.println("Valid Password!");
            } else { 
            	System.out.println("Error - Invalid Password!");
            }
            System.out.println();
            
            System.out.println("2. 사용자 로그인 ");
            System.out.print("로그인하려면 패스워드를 입력하세요>> ");
            String password1 = a.next();
            System.out.println("사용자가 입력한 패스워드(Pass): "+password1);
            if(validatePassword(password1, hash)) {
            	System.out.println("--->로그인 완료");
          	} else System.out.println("Error - Invalid Password!");
            System.out.println();
            
            System.out.println("3. 서버가 로그인된 사용자에게 토큰 발급 "); 
            Mac mac = Mac.getInstance("HmacSHA1");
			mac.init(keySpec);
			mac.update(id.getBytes());
			byte[] publicToken = mac.doFinal();
			System.out.println("공개토큰: PubToken=HMAC(ID,기기명,유효기간,K)"); 
			System.out.println("공개토큰: "+bytesToHex(publicToken));
			mac.update(publicToken);
			byte[] secretToken = mac.doFinal();
			System.out.println("비밀토큰: SecToken=HMAC(PubToken,K)");
			System.out.println("비밀토큰: "+bytesToHex(secretToken));
			System.out.println();
			
			while(true) {
				System.out.print("자동로그인을 할까요?>> (y/n) ");
	            String yn= a.next();
	            System.out.println();
	            
	            if(yn.equalsIgnoreCase("y")) {
					System.out.println("4. 토큰을 이용한 자동 로그인 ");
					long curr1 = System.currentTimeMillis();  
					SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy:MM:dd-hh:mm:ss");
					String datetime1 = sdf1.format(new Date(curr1));
					System.out.println("현재시간(T): " + datetime1);
					
					byte[] autoLoginToken = generateAutoLoginToken(secretToken, datetime1);
					System.out.println("서버에게 전송되는 공개토큰: "+bytesToHex(publicToken));
					System.out.println("자동로그인토큰: AutoLoginToken=H(SecToken,T)");
					System.out.println("서버에게 전송되는 자동로그인 토큰: "+bytesToHex(autoLoginToken));
					System.out.println();
								
					System.out.println("5. 서버의 자동 로그인 검증 ");
					if(verifyAutoLoginToken(mac, publicToken, datetime1, autoLoginToken)) 
						System.out.println("---> 자동로그인 허가");
					else 
						System.out.println("자동로그인 거부 - 다시 로그인 하세요."); 
					long curr2 = System.currentTimeMillis();  
					SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy:MM:dd-hh:mm:ss");
					String datetime2 = sdf2.format(new Date(curr2));
					System.out.println("현재시간: " + datetime2);
					long dt = curr2 - curr1;
					System.out.println("시간차이: " + dt +" msec");
					System.out.println();
	            }
	            else break;
			}
        }
        catch(Exception ex)
        {
        	System.out.println("ERROR: " + ex);
        }
    }
}