/**
 * Uses asymmetric encryption to encrypt the unencryptedBytes using the public key of the recipient.
 * @param unencryptedBytes bytes to encrypt
 * @param recipient identifier of the recipient
 * @param ASAPKeyStore key store that holds the public key of the recipient
 * @return encrypted bytes
 * @throws ASAPSecurityException if the public key is missing or other problems occurred during encryption
 */
public static byte[] encryptAsymmetric(byte[] unencryptedBytes, CharSequence recipient, ASAPKeyStore ASAPKeyStore) throws ASAPSecurityException {
    PublicKey publicKey = ASAPKeyStore.getPublicKey(recipient);
    if (publicKey == null) {
        throw new ASAPSecurityException("recipients' public key cannot be found");
    } else {
        try {
            Cipher cipher = Cipher.getInstance(ASAPKeyStore.getAsymmetricEncryptionAlgorithm());
            cipher.init(1, publicKey);
            return cipher.doFinal(unencryptedBytes);
        } catch (InvalidKeyException | NoSuchPaddingException | IllegalBlockSizeException | BadPaddingException |
                 NoSuchAlgorithmException e) {
            throw new ASAPSecurityException("problems when encrypting", e);
        }
    }
}