Data Encryption Decryption using AES Algorithm, Key and Salt with Java Cryptography Extension

In this tutorial we will implement a full data encryption decryption cycle with Java (only data, not file encryption); encrypt some data using a secret key, salt and iterations and decrypt using the same parameters. We are using the Java Cryptography Extension (JCE) for data encryption/decryption operations. This extension is available in Java 1.4.2 and above; you will have to manually download it for older versions (here). Java supports a number of of encryption algorithms, however we will demonstrate only AES algorithm (the Advanced Encryption Standard) usage.

Why should we encrypt data?

Encryption and Decryption are highly important security steps; now there are file and data encryption software as well. Data encryption is the mechanism of converting a message (plain text) into some other text (called ciphertext) so that readers can not understand the original message; however some authorized party can understand that ciphertext using the method called Decryption which converts the ciphertext into original message. As many software applications store sensitive personal data in databases, encryption has become a must. Ideally nobody (including the software developers) should not be able to view these user specific real data.

Simple Data Encryption/Decryption Example with AES

For encryption we must use a secret key along with an algorithm. In the following example we use an algorithm called AES 128 and the bytes of the word "ThisIsASecretKey" as the secret key (the best secret key we found in this world). AES algorithm can use a key of 128 bits (16 bytes * 8); so we selected that key.

package org.kamal.crypto;

import java.security.*;
import java.security.spec.InvalidKeySpecException;
import javax.crypto.Cipher; 
import javax.crypto.spec.SecretKeySpec;
import sun.misc.*;

public class SimpleProtector {

    private static final String ALGORITHM = "AES";
    private static final byte[] keyValue = 
        new byte[] { 'T', 'h', 'i', 's', 'I', 's', 'A', 'S', 'e', 'c', 'r', 'e', 't', 'K', 'e', 'y' };

    public static String encrypt(String valueToEnc) throws Exception {
        Key key = generateKey();
        Cipher c = Cipher.getInstance(ALGORITHM);
        c.init(Cipher.ENCRYPT_MODE, key);
        byte[] encValue = c.doFinal(valueToEnc.getBytes());
        String encryptedValue = new BASE64Encoder().encode(encValue);
        return encryptedValue;
    }

    public static String decrypt(String encryptedValue) throws Exception {
        Key key = generateKey();
        Cipher c = Cipher.getInstance(ALGORITHM);
        c.init(Cipher.DECRYPT_MODE, key);
        byte[] decordedValue = new BASE64Decoder().decodeBuffer(encryptedValue);
        byte[] decValue = c.doFinal(decordedValue);
        String decryptedValue = new String(decValue);
        return decryptedValue;
    }

    private static Key generateKey() throws Exception {
        Key key = new SecretKeySpec(keyValue, ALGORITHM);
        // SecretKeyFactory keyFactory = SecretKeyFactory.getInstance(ALGORITHM);
        // key = keyFactory.generateSecret(new DESKeySpec(keyValue));
        return key;
    }
}

We use "generateKey()" method to generate a secret key for AES algorithm with a given key. You can change the used algorithm by changing this Key generation; the commented out code shows the use of DES algorithm (Data Encryption Standard). Following is a simple class to test the above implementation.

package org.kamal.crypto;

public class TestSimpleProtector {

    public static void main(String[] args) throws Exception {

        String password = "mypassword";
        String passwordEnc = SimpleProtector.encrypt(password);
        String passwordDec = SimpleProtector.decrypt(passwordEnc);

        System.out.println("Plain Text : " + password);
        System.out.println("Encrypted : " + passwordEnc);
        System.out.println("Decrypted : " + passwordDec);
    }
}

Following is the output we got from above test; so you clearly see that the original text is reproduced after the decryption operation.

Plain Text : mypassword
Encrypted : sBhCap4urE50a/dGuhNgrw==
Decrypted : mypassword

The encrypted value is not simply related to the plain text, so it provides some security to the password.

The Risk with Simple Protector

When you use the above mentioned method to encrypt all passwords in your database, it makes an attacker's task easier. Since the same key is used, if an attacker find a way to get the plain text, the he can use that same method to get all the other plain-texts in the database in minutes.

Use Salt and iterations to improve

To make the attackers job harder we can use two methods; called adding Salt and using Iterations.
A Salt is another plain-text appended to the given plain text, before generating the encrypted value. We use a unique Salt per each plain-text so that the value used to encrypt is getting much stronger making it harder for an attacker to guess with a brute force or dictionary attack. Following class shows the improved version of SimpleProtector class.

package org.kamal.crypto;

import java.security.*;
import java.security.spec.InvalidKeySpecException;
import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import sun.misc.*;

public class Protector {

    private static final String ALGORITHM = "AES";
    private static final int ITERATIONS = 2;
    private static final byte[] keyValue = 
        new byte[] { 'T', 'h', 'i', 's', 'I', 's', 'A', 'S', 'e', 'c', 'r', 'e', 't', 'K', 'e', 'y'};

    public static String encrypt(String value, String salt) throws Exception {
        Key key = generateKey();
        Cipher c = Cipher.getInstance(ALGORITHM);  
        c.init(Cipher.ENCRYPT_MODE, key);
  
        String valueToEnc = null;
        String eValue = value;
        for (int i = 0; i < ITERATIONS; i++) {
            valueToEnc = salt + eValue;
            byte[] encValue = c.doFinal(valueToEnc.getBytes());
            eValue = new BASE64Encoder().encode(encValue);
        }
        return eValue;
    }

    public static String decrypt(String value, String salt) throws Exception {
        Key key = generateKey();
        Cipher c = Cipher.getInstance(ALGORITHM);
        c.init(Cipher.DECRYPT_MODE, key);
  
        String dValue = null;
        String valueToDecrypt = value;
        for (int i = 0; i < ITERATIONS; i++) {
            byte[] decordedValue = new BASE64Decoder().decodeBuffer(valueToDecrypt);
            byte[] decValue = c.doFinal(decordedValue);
            dValue = new String(decValue).substring(salt.length());
            valueToDecrypt = dValue;
        }
        return dValue;
    }

    private static Key generateKey() throws Exception {
        Key key = new SecretKeySpec(keyValue, ALGORITHM);
        // SecretKeyFactory keyFactory = SecretKeyFactory.getInstance(ALGORITHM);
        // key = keyFactory.generateSecret(new DESKeySpec(keyValue));
        return key;
    }
}

You need to store the clear Salt with the stored encrypted value since the salt is required at the decrypt operation. We just used a sentence as the 'salt', but you should use a random letters/numbers for that to avoid any dictionary attacks.

package org.kamal.crypto;

public class TestProtector {

    public static void main(String[] args) throws Exception {
        String password = "mypassword";
        String salt = "this is a simple clear salt";
        String passwordEnc = Protector.encrypt(password, salt);
        String passwordDec = Protector.decrypt(passwordEnc, salt);

        System.out.println("Salt Text : " + salt);
        System.out.println("Plain Text : " + password);
        System.out.println("Encrypted : " + passwordEnc);
        System.out.println("Decrypted : " + passwordDec);
    }
}

The output from the above class looks as follows.

Salt Text : this is a simple clear salt
Plain Text : mypassword
Encrypted : GX8jEr04o6PC+IE+f6DXq+zuRiZ2nsSL+UYxYRh9vK28xt/GrLqnbrP3hkXSW5S3jNgzXkrLSmXm
fwRw+eBMWQJO+8tlSEE9D2Y9qEzowX18s4W81U/D9JL3JX7uJtwp
Decrypted : mypassword

When using Salt, you can store each (clear text) Salt in the database per each encrypted text. It would be better if we pass the secrete key while initializing or instantiating the (Protector) encryption class rather than hard coding it in the class itself (for simplicity we used a hard coded key for this tutorial).

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