1. Generate a key
2. Share this key with B
3. Encrypt data with this key
4. Transmit encrypted data to B

import java.io.BufferedInputStream;

import java.io.BufferedOutputStream;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.security.InvalidKeyException;

import java.security.NoSuchAlgorithmException;

import java.security.SecureRandom;

import javax.crypto.BadPaddingException;

import javax.crypto.Cipher;

import javax.crypto.IllegalBlockSizeException;

import javax.crypto.KeyGenerator;

import javax.crypto.NoSuchPaddingException;

import javax.crypto.SecretKey;

import javax.crypto.ShortBufferException;

/**

 *

 */

public class AESEncrypt {

    public static void main(String[] args) throws NoSuchAlgorithmException, IOException,

            NoSuchPaddingException, InvalidKeyException, ShortBufferException,

            IllegalBlockSizeException, BadPaddingException {

        // Generate key and store into file

        SecureRandom random = new SecureRandom(); // see below

        KeyGenerator keyGen = KeyGenerator.getInstance("AES");

        keyGen.init(random);

        SecretKey secretKey = keyGen.generateKey();

        FileOutputStream secretKeyOut = new FileOutputStream(Util.PATH_SECRETKEY);

        secretKeyOut.write(secretKey.getEncoded());

        secretKeyOut.close();

        // Cipher

        Cipher aesCipher = Cipher.getInstance("AES");

        aesCipher.init(Cipher.ENCRYPT_MODE, secretKey);

        // Encrypt

        BufferedInputStream dataIn = new BufferedInputStream(new FileInputStream(Util.PATH_DATA));

        BufferedOutputStream encryptedDataOut = new BufferedOutputStream(new FileOutputStream(Util.PATH_DATA_ENCRYPTED));

        byte[] inBytes = new byte[aesCipher.getBlockSize()];

        byte[] outByte;

        int len;

        while ((len = dataIn.read(inBytes)) >= 0) {

            outByte = aesCipher.update(inBytes, 0, len);

            encryptedDataOut.write(outByte);

        }

        outByte = aesCipher.doFinal();

        encryptedDataOut.write(outByte);

        dataIn.close();

        encryptedDataOut.close();

    }

}

3. Decryption

import java.io.BufferedInputStream;

import java.io.BufferedOutputStream;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.security.InvalidKeyException;

import java.security.NoSuchAlgorithmException;

import javax.crypto.BadPaddingException;

import javax.crypto.Cipher;

import javax.crypto.IllegalBlockSizeException;

import javax.crypto.NoSuchPaddingException;

import javax.crypto.SecretKey;

import javax.crypto.spec.SecretKeySpec;

/**

 * Class documentation to be filled TODO

 */

public class AESDecrypt {

    public static void main(String[] args) throws IOException, ClassNotFoundException,

            NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException,

            IllegalBlockSizeException, BadPaddingException {

        // Get key

        FileInputStream secretKeyIn = new FileInputStream(Util.PATH_SECRETKEY);

        byte[] secretKeyBytes = new byte[secretKeyIn.available()];

        secretKeyIn.read(secretKeyBytes);

        secretKeyIn.close();

        SecretKey secretKey = new SecretKeySpec(secretKeyBytes, "AES");

        // Cipher

        Cipher aesCipher = Cipher.getInstance("AES");

        aesCipher.init(Cipher.DECRYPT_MODE, secretKey);

        // Decrypt

        BufferedInputStream encryptedDataIn = new BufferedInputStream(new FileInputStream(Util.PATH_DATA_ENCRYPTED));

        BufferedOutputStream decryptedDataOut = new BufferedOutputStream(new FileOutputStream(Util.PATH_DATA_DECRYPTED));

        byte[] inBytes = new byte[aesCipher.getBlockSize()];

        byte[] outBytes;

        int len;

        while ((len = encryptedDataIn.read(inBytes)) >= 0) {

            outBytes = aesCipher.update(inBytes, 0, len);

            decryptedDataOut.write(outBytes);

        }

        outBytes = aesCipher.doFinal();

        decryptedDataOut.write(outBytes);

        encryptedDataIn.close();

        decryptedDataOut.close();

    }

}