Password Based Encryption Using AES

In a recent engagement, i needed to encrypt an object then write it to disk. I wanted to use Advanced Encryption Standard(AES), but unfortunately Java does not provide a way to use password based encryption with AES.

Bouncy Castle does provide the required libraries that will allow us to use password based encryption with AES.

In this scenario, i wanted the user to provide the pass phrase.

//name of the algorithm to use
static String algorithm = "PBEWITHSHA256AND128BITAES-CBC-BC";

static char[] passPherase = "secretpass".toCharArray();
static byte[] salt = "a9v5n38s".getBytes();
static String secretData = "Very Secret Data!!";

In real world you should generate the salt randomly. We need to create a key spec based on the user input then create a cipher for encrypting or decrypting the data.

Encrypting the data

    static SealedObject encrypt(String data) throws Exception{
        PBEParameterSpec pbeParamSpec = new PBEParameterSpec(salt,20);
        PBEKeySpec pbeKeySpec = new PBEKeySpec(passPherase);
        SecretKeyFactory secretKeyFactory = 
            SecretKeyFactory.getInstance(algorithm);
        SecretKey secretKey = secretKeyFactory.generateSecret(pbeKeySpec);

        Cipher cipher = Cipher.getInstance(algorithm);
        cipher.init(Cipher.ENCRYPT_MODE,secretKey,pbeParamSpec);

        return new SealedObject(data,cipher);
    }

Decrypting the data back again

    static String decrypt(SealedObject sealedObject) throws Exception{
        PBEParameterSpec pbeParamSpec = new PBEParameterSpec(salt,20);
        PBEKeySpec pbeKeySpec = new PBEKeySpec(passPherase);
        SecretKeyFactory secretKeyFactory = 
            SecretKeyFactory.getInstance(algorithm);
        SecretKey secretKey = secretKeyFactory.generateSecret(pbeKeySpec);

        Cipher cipher = Cipher.getInstance(algorithm);
        cipher.init(Cipher.DECRYPT_MODE,secretKey,pbeParamSpec);
        return (String)sealedObject.getObject(cipher);
    }

Using a SealedObject you can basically encrypt any object you want, and serialize it to a file.

    public static void main(String[] args) {
        try{
            Security.addProvider(new BouncyCastleProvider());

            SealedObject encryptedString = encrypt(secretData);

            String decryptedString = decrypt(encryptedString);

            System.out.println(decryptedString);

        }catch( Exception e ) { 
            System.out.println(e.toString());
        }
    }

Download code

Tags: java encryption

nakkayadotcom