Appendix A: Java Code Sample: Auth Header Generation

private static final String AUTH_HEADER_SCHEME = "TrSvcAreaAuthHeader";
private static final int  BUFFER_SIZE = 4 * 1024 * 1024;

private String buildAuthHeader() throws ThruTransportException {
		logger.debug("[buildAuthHeader] Constructing Authorization header...");
		try {
			DateTime now = new DateTime(DateTimeZone.UTC);
			DateTimeFormatter formatter = DateTimeFormat.forPattern("yyyy-MM-dd-HH-mm-ss");
			String date = formatter.print(now);
			String authHeader = String.format("%s|%s|%s", "1.0" /* API Version */, SECRET_KEY, date);
			String val = String.format("%s %s", AUTH_HEADER_SCHEME, encrypt(authHeader));

			logger.debug("[buildAuthHeader] Authorization header constructed: %s", val);

			return val;
		} catch(Exception ex){
			logger.error("[buildAuthHeader] Unable to construct Authorization header", ex);
            System.out.print(ex.getMessage());
			throw new ThruTransportException("[buildAuthHeader]" + ex.getMessage(), MFTErrorType.UNABLE_BUILD_AUTH_HEADER);
		}
	}

	private String encrypt(String data) throws Exception {
		logger.debug("[encrypt] Encrypting data: %s", data);

		byte[] salt = generateSalt();	
		Cipher cipher = buildCipher(salt);
		byte[] encrypted = cipher.doFinal(data.getBytes("UTF-16LE"));
		
		byte[] result = new byte[salt.length + encrypted.length];
		System.arraycopy(salt, 0, result, 0, salt.length);
		System.arraycopy(encrypted, 0, result, salt.length, encrypted.length);
		String base64String = Base64.encodeBytes(result, Base64.DONT_BREAK_LINES);
		logger.debug("[encrypt] Data encrypted: %s", base64String);
		return base64String;
	}

 
private Cipher buildCipher(byte[] salt) 
			throws 	NoSuchAlgorithmException, 
					NoSuchPaddingException, 
					InvalidKeySpecException, 
					InvalidKeyException, 
					InvalidAlgorithmParameterException
	{
		logger.debug("[buildChiper] Configuring cipher for encryption");
		SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
		PBEKeySpec pbeKeySpec = new PBEKeySpec(ENCRYPTION_KEY.toCharArray(), salt, 1000, 256);
		Key secretKey = factory.generateSecret(pbeKeySpec);
		
		byte[] keyBytes = new byte[16];
		byte[] ivBytes = new byte[16];
	
		System.arraycopy(secretKey.getEncoded(), 0, keyBytes, 0, 16);
		System.arraycopy(secretKey.getEncoded(), 16, ivBytes, 0, 16);
		
		Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
		
		SecretKeySpec keySpec = new SecretKeySpec(keyBytes, "AES");
		AlgorithmParameterSpec iv = new IvParameterSpec(ivBytes);
		
		cipher.init(Cipher.ENCRYPT_MODE, keySpec, iv);
		
		return cipher;
	}

	private byte[] generateSalt() {
		logger.debug("[generateSalt] Generating salt");
		byte[] salt = new byte[8];
		Random rand = new SecureRandom();
		rand.nextBytes(salt);
		
		return salt;
	}