PHP 5.5
PHP 5.5 is a release of the PHP language shipped in June 2013 that brought several changes important for application performance and security. The most significant was bundling the OPcache mechanism directly into the language core, which sped up script execution without the need to install a separate extension.
Why PHP 5.5 mattered
PHP 5.5 focused on maturing the language and better protecting user data:
- OPcache — a built-in cache of compiled bytecode that cuts execution time for repeated requests;
- generators (yield) — lazy processing of large data sets without loading everything into memory;
- a new password API — the password_hash and password_verify functions, which simplify secure password storage;
- the finally block — fuller exception handling in try/catch constructs.
The built-in password API was especially significant — it encouraged developers to abandon weak hashing functions in favour of modern, attack-resistant algorithms.
Practical applications
Official support for PHP 5.5 ended in 2016, so today it is an obsolete version. Even so, its legacy lives on: OPcache and the password API are standard parts of modern PHP. Applications still running on this version should be updated for security reasons. Modern hosting and VPS servers offer only supported releases, and migrating from PHP 5.5 to a newer branch, such as PHP 5.6, is usually fairly straightforward thanks to the similar syntax.
Impact on password security
The greatest practical legacy of PHP 5.5 remains its built-in password API. Before it appeared, developers often used outdated hashing functions that were vulnerable to rainbow-table attacks. The password_hash and password_verify functions hid the complexity of secure salting and algorithm selection behind a simple interface, so even less experienced developers could store user passwords in line with current standards. That solution is still used today in unchanged form.