When I was a kid, WEP had a 40 bit key. Later, they came out with a 128-bit key. But as we all know, WEP was so badly-designed that the RC4 key length didn't really matter much.
Ignoring this, my question is about how to derive the 40-bit or 128-bit key from an ASCII string: this used to be platform-specific. In other words, you could enter the 40 or 128-bit key in hex form (which worked no matter the platform) or you could enter it as an ASCII phrase, which would then be turned into the underlying WEP key in some platform-specific manner, and sometimes incompatibilities would arise.
Nowadays, it seems like ASCII passwords are universal and things always work. Can someone explain how this works? Is there a standard you can point me to?