Crypto++ AES-256 CBC mode supports Windows XP, but I want to know whether GCM ciphor mode also supports Windows XP?
Topic on Project:Support desk
Your question doesn't seem related to MediaWiki. Maybe you're asking on the wrong site?
It might be related to Manual:$wgSessionInsecureSecrets. I have added information on the different encryption mechanisms to that page some time ago.
The important thing is the PHP version I guess. If you are running a rather new version of PHP, chances are that the necessary algorithms will be in as well.
On Windows XP, the last version of PHP, which you can run, is PHP 5.4. This version allows you to run any version of MediaWiki up to MediaWiki 1.26, but not MW 1.27.
With other words: MediaWiki 1.27, in which $wgSessionInsecureSecrets has been introduced as a new option, will not work on Windows XP. So basically, if you are running on Windows XP, $wgSessionInsecureSecrets and its possible values are irrelevant for you.