marchfeld

Currently supported password encryptions are mysql OLD_PASSWORD and mysql PASSWORD, so if you have migrate from application with user’s passwords encrypted with those two methods it will enable them to login.
This is useful if you don’t want to force all existing users to reset password.

Custom password encryption

Custom password encryption enable to login for imported users with other password encryption then the default md5 encryption.

palicao

This plugin adds a new permalink tag %hashed_id% which represents the encrypted 
version of your post ID. 
Uses hashids library (see http://www.hashids.org/php/).
With this plugin you can change your permalink structure into something like
<pre><code>/%hashed_id%/ 
</code></pre>
to obtain links like
<pre><code>http://www.example.com/B7j1rPk8
</code></pre>
or into something like
<pre><code>/%year%/%monthnum%/%hashed_id%/
</code></pre>
to obtain URLs like
<pre><code>http://www.example.com/2012/10/B7j1rPk8
</code></pre>
or
<pre><code>/%hashed_id%/%postname%/
</code></pre>
to obtain
<pre><code>http://www.example.com/B7j1rPk8/my-slug
</code></pre>
This plugin is useful when you want to obfuscate the number of posts or simply 
if you want an unusual and concise url schema. This is also useful if you want to have 
short URLs without using a third-party service.

WP Hashed IDs

This plugin adds a new permalink tag %hashed_id% which represents the encrypted

Custom password encryption vs WP Hashed IDs