In a recent post Marcus Bointon looks at a hashing method that's not one as commonly used by developers as the usual base64 - base-62 encoding that plays a bit nicer with things like URLs and emails due to the character set it allows.

There's a really horrible bug (though they won't call it that!) in Apache's mod_rewrite that means that urlencoded inputs in rewrites get unescaped in their transformation to output patterns. The bug actually remains unfixed, though a workaround first appeared in Apache 2.2.12. [...] Base-62 is interesting as it can be made safe for use in URLs, DNS, email addresses and pathnames, unlike any available encoding of base-64, as it only includes [0-9A-Za-z].

He originally wrote his own parser, but notes that now the BCMath and gmp extensions make it much simpler, just a call to gmp_strval with gmp_init. This method works, but it's still not quite all he wanted so he created his own encoder to do the job.

In an effort to just about everything he can with PHP Mark Karpeles has posted an article about how he created a SSH server in PHP with most (not quite all) of the functionality of some of its counterparts.

You probably know SSH at least by its name. It's a of secure telnet replacement which also allows many other things such as port forwarding, remote file management (with sftp) and more. With PHP I could write a fully working SSH server in only 3 days. [...] My goal when writing this was to provide a replacement for the FTP protocol for the customers of my hosting service.

He lists the extensions used to create the extension - OpenSSL, mcrypt, hash and (the most important) GMP as well as a link to the source if you'd like to try it out yourself.