Authenticating with HMAC in Java
Introduction to HMAC in Java
HMAC (Hash-based Message Authentication Code) is a cryptography technique that can be used to verify the integrity of data sent between two parties. It is often used as a way to ensure data security and integrity, as HMAC prevents potential manipulation of data by third-party entities. Additionally, HMAC can also be used to provide authentication between the two communicating parties.
In Java, the HMAC implementation is achieved using the Mac class and its init, update and doFinal methods. In this article, we will look at an example of how to use the Mac class to build a simple HMAC authentication system in Java.
Example of HMAC Authentication System in Java
First, we need to import the necessary classes for our example. We will need the Mac class from the javax.crypto package, and the java.security.spec.KeySpec interface from the java.security.spec package.
import javax.crypto.Mac;
import java.security.spec.KeySpec;
Next, we will define the key which will be used to sign and verify the data. This key could be shared between parties or publicly available.
byte[] key = { 0x60, 0x51, 0x41, 0x30, 0x20, 0x11, 0x04, 0x70 };
We will then create the Mac instance which is used to generate and verify the HMAC signature. For this, we need to call the getInstance() static method from the Mac class and pass it the HMAC algorithm name.
Mac mac = Mac.getInstance("HmacSHA256");
Now, we will initialize the Mac instance with the secret key. This is done by passing the secret key to the init() method of the Mac class.
KeySpec keySpec = new SecretKeySpec(key, "HmacSHA256");
mac.init(keySpec);
At this point, the Mac instance is ready to be used for generating and verifying HMAC signatures. To generate the HMAC signature, we simply need to call the update() method of the Mac instance, passing it the data we want to sign, followed by the doFinal() method.
String message = "This is the message to be signed";
mac.update(message.getBytes());
byte[] hmacSignature = mac.doFinal();
The hmacSignature is the HMAC signature generated by the Mac instance. This signature can then be sent to the other party, along with the message, for verification.
To verify the signature, the other party would need to call the update() and doFinal() method, passing them the same message and signature. If the output of the doFinal() method is the same as the signature received, then the message is authentic.
mac.update(message.getBytes());
if (Arrays.equals(mac.doFinal(), hmacSignature))
{
// message is authentic
}
That's all there is to setting up an HMAC authentication system in Java. As you can see, the Mac class makes it very easy to generate and verify HMAC signatures in Java.