title: How to verify a digital signature with openssl
body: <p>I'm using a thirdparty credit card processing service (Paybox) that, after a successful transaction, redirects back to the website with a signature in the URL as a security measure to prevent people from manipulating data. It's supposed to prove that the request originated from this service. So my success URL looks something like this:</p>
  
  <p>/success.php?signature=[HUGE HASH]</p>
  
  <p>I have no idea where to start with verifying this signature. This service does provide a public key, and I assume I need to create a private key, but I don't know much beyond that. </p>
  
  <p>I'm pretty good with linux, and I know I'll have to run some openssl commands. I'm writing the verification script in PHP, which also has native openssl() functions.</p>
  
  <p>If anyone could please push me in the right direction with some pseudo code, or even functional code, I'd be very grateful. Thanks.</p>