On the php[architect] site they've posted an article that appeared in their December 2017 issue, an article that introduces Libsodium (by Eric Mann), a new addition to PHP's "security toolbelt" for encryption.

By the time you read this, the PHP community should have introduced the world to the newest version of our favorite language. This latest version adds better support for type annotations, allows trailing commas in lists (just like JavaScript and other dynamic languages) and introduced several security improvements. The most notable security addition, however, is the introduction of the Sodium cryptographic library as a core extension.

In the article he covers the basics of the Sodium library (that libsodium is built on top of) and what makes it different from other encryption methods. He also talks about what's been done to support it on pre-PHP 7.2 versions including the sodium_compat polyfill library and the PECL extension for PHP 7.0+. Example code is included showing how to use this new functionality via native functions once support for it has been compiled in.