Secure XML-RPC

FAQ

How do I use the new authorization?

The old username/password paradigm can still be used, but will result in a X-Deprecated header being returned by the server.

From now on, you will send an Authorization header. This header will be the publishing application’s public key, two pipe (|) characters, and a hash of the application’s secret key concatenated with the body of the request.

How do I generate the message hash?

Say your application has the following information:
* Public Key: b730db0864b0d4453ba6a26ad6613cd4
* Secret Key: 7647a19f5bf3e9fd001419900ad48a54

And you want to make the following request (whitespace/indentation added for readability, but is removed when calculating hashes):

<?xml version="1.0"?>
<methodCall>
  <methodName>wp.getPosts</methodName>
  <params>
    <param>
      <value><i4>1</i4></value>
    </param>
    <param>
      <value><string></string></value>
    </param>
    <param>
      <value><string></string></value>
    </param>
  </params>
</methodCall>

Note that the second and third parameters (traditionally username and password) are empty. Usernames and passwords can still be specified, but will result in the server returning an X-Deprecated header.

Your Authorization header would thus become:

b730db0864b0d4453ba6a26ad6613cd4||3fac15f99f7a178f922bcc4942e62dc9001b2a45118fc3a6f3aebd77d25f4d58

The second part of the header is generated in PHP by calculating:

hash( 'sha256', '7647a19f5bf3e9fd001419900ad48a54' . hash( 'sha256', '7647a19f5bf3e9fd001419900ad48a54' . {request_body} ) )

WordPress will read the header and log you in as usual, but you never need to send your password across the wire.

In this paradigm, application secret keys should also be treated as passwords – they are sensitive information!

Why are we using the secret key twice?

Some developers raised concerns about length extension attacks in previous editions of the plugin. While length extension isn’t strictly necessary when dealing with XML-based messaging, a double hash helps end the discussion around potentially-related vulnerabilities.

The double-hash is similar to but simpler than HMAC and is fairly easy to implement in any programming language. Just note, PHP’s hash() function returns a base64-encoded string, not a raw hash of the data passed in.

Do I have to copy/paste my application keys into remote systems?

Not necessarily.

The latest version of the plugin adds a new XML-RPC method to the system that allows for the generation of user-specific application keys remotely. Please only ever call this method over a secure/trusted network connection when setting up an application for the first time.