hash_hmac PHP: Purpose & Usage Guide

The hash_hmac function in PHP is used to generate a Message Authentication Code (MAC) with a key. HMAC is a technique used for ensuring the integrity and authentication of a message. It generates a fixed-length digest by hashing the key and the message, then attaching this digest to the message. This allows the recipient to use the same key and algorithm to verify the integrity of the message.

The hash_hmac function takes four parameters: the hashing algorithm, the data to compute the HMAC for, the key to compute the HMAC with, and a boolean value to specify if the output should be raw binary data. An example of how to use it is as follows:

$key = 'secret-key';
$data = 'hello world';
$hmac = hash_hmac('sha256', $data, $key);

echo $hmac;

In the example above, we used the sha256 algorithm and the key ‘secret-key’ to generate a message authentication code, and then printed it out. Using the hash_hmac function ensures the integrity and authentication of the message.