The default WordPress “shortlink” URLs look like this: <code>http://www.example.com/blog/?p=123</code>, where “<code>123</code>” is actually a 7+ digit decimal number. This plugin shrinks your shortlinks by encoding that number into only 4 characters, and using the abbreviated URL prefix of your choice.
On my site, the default shortlinks are 35 bytes long, even though I have a very short domain name. This plugin shrinks them to 21 total bytes, which is comparable to most public URL-shortener services, and better than many.
E.g., this: <code>http://www.jwz.org/blog/?p=13240780</code> 
becomes: <code>http://jwz.org/b/ygnM</code>
This doesn’t affect your (long) permalinks: those can still be in whatever format you like.

Base64 Shortlinks

This plugin makes your shortlinks shorter!

Ryan Street

Jason Grim

Background
WordPress has created the wonderful functionality of generating shortlinks for post on your blogs. With advanced 
permalink structures a single link to your site can take up 89% of a short email or a facebok update. However, 
Wordpress created a very ugly system, the shortlink system simply provides the default permalink structure with ugly 
url variables.
Here is the documentation on adding shortlinks to your themes on the <a href="https://codex.wordpress.org/Function_Reference/the_shortlink" title="Wordpress.org - Shortlinks" rel="nofollow ugc">WordPress Codex</a>
Use
Some themes use the template method to share the short url of your post. The use of this plugin would convert all of those 
links to trackable ones with bit.ly or shorter ones with the other services.
Also, when you create a new post a button is created next the the URL of your new post. If you click the “Get Shortlink” button 
a popup will provide a simple little link to share with all of your friends and fans.

Generate Shortlinks

Uses bit.ly, Ur.ly, and Is.gd to create handy shortlinks to share your WordPress Posts quickly and easily!

Base64 Shortlinks vs Generate Shortlinks