Development Shack Technology Understood

There are a lot of examples out there but none of the articles I found were are concise enough and provided both the generation and usage of the secret keys.

Click here to view the source code

Generating a Secret Key

public class CryptStream {
    public final static String CIPHER_TYPE = "DESede/ECB/PKCS5Padding";
    public final static String CIPHER_NAME = "DESede";

    public static byte[] generateNewSecretKey() {
        KeyGenerator keyGenerator;
        try {
            keyGenerator = KeyGenerator.getInstance(CIPHER_NAME);
            return keyGenerator.generateKey().getEncoded();
        } catch (NoSuchAlgorithmException e) {
            ErrorHandling.handleException(String.format("Generating Cipher Key: %s", CIPHER_NAME), e);
        }

        return null;
    }
}

Save the Secret Key somewhere safe

public class CryptStream {
    public final static String CIPHER_TYPE = "DESede/ECB/PKCS5Padding";
    public final static String CIPHER_NAME = "DESede";

    private final static byte[] SECRET_KEY = new byte[] {
        ...
    };
}

Create and initialize a Cipher

Cipher cipher = Cipher.getInstance(CIPHER_TYPE);
cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(SECRET_KEY, CIPHER_NAME));

Using CryptInputStream and CryptOutputStream

inputStream = new CipherInputStream(inputStream, cipher);
outputStream = new CipherOutputStream(outputStream, cipher);

A Complete Code listing

import java.io.InputStream;
import java.io.OutputStream;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;

import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.CipherOutputStream;
import javax.crypto.KeyGenerator;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.SecretKeySpec;

public class CryptStream {
    public final static String CIPHER_TYPE = "DESede/ECB/PKCS5Padding";
    public final static String CIPHER_NAME = "DESede";

    private final static byte[] SECRET_KEY = new byte[] {
        ...
    };

    public static byte[] generateNewSecretKey() {
        KeyGenerator keyGenerator;
        try {
            keyGenerator = KeyGenerator.getInstance(CIPHER_NAME);
            return keyGenerator.generateKey().getEncoded();
        } catch (NoSuchAlgorithmException e) {
            ErrorHandling.handleException(String.format("Generating Cipher Key: %s", CIPHER_NAME), e);
        }

        return null;
    }

    public static InputStream decryptSteam(InputStream inputStream) {
        try {
            Cipher cipher = Cipher.getInstance(CIPHER_TYPE);
            cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(SECRET_KEY, CIPHER_NAME));

            return new CipherInputStream(inputStream, cipher);
        } catch (NoSuchAlgorithmException e) {
            ErrorHandling.handleException(String.format("Initializing the Cipher: %s", CIPHER_NAME), e);
        } catch (NoSuchPaddingException e) {
            ErrorHandling.handleException(String.format("Initializing the Cipher: %s", CIPHER_NAME), e);
        } catch (InvalidKeyException e) {
            ErrorHandling.handleException(String.format("Initializing the Cipher Key: %s", CIPHER_NAME), e);
        }

        return null;
    }

    public static OutputStream encryptStream(OutputStream outputStream) {

        try {
            Cipher cipher = Cipher.getInstance(CIPHER_TYPE);
            cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(SECRET_KEY, CIPHER_NAME));

            return new CipherOutputStream(outputStream, cipher);
        } catch (NoSuchAlgorithmException e) {
            ErrorHandling.handleException(String.format("Initializing the Cipher: %s", CIPHER_NAME), e);
        } catch (NoSuchPaddingException e) {
            ErrorHandling.handleException(String.format("Initializing the Cipher: %s", CIPHER_NAME), e);
        } catch (InvalidKeyException e) {
            ErrorHandling.handleException(String.format("Initializing the Cipher Key: %s", CIPHER_NAME), e);
        }

        return null;
    }

}

And now you can use this anywhere:

InputStream inputStream = CryptStream.decryptSteam(new FileInputStream(...));
inputStream.close();

You can change the CIPHER_NAME, and CIPHER_TYPE constants to use another algorithm.