PHP常用加密的库与例子，还有手册,包含DES,RAS,SSH1,SSH2-Although many of the features this library implements are implemented in PHP via optional extensions, what are you, as a developer, going to do when a user tries to run your software on a host which, coincidentally, doesn t happen to have that optional extension installed? You could, flat-out, tell that user to look for another software package that does work on their server (or to get another host, or whatever), which is liable to leave a bad impression on the user, or you could use a library like this- a library that uses those optional extensions if they re available and falls back on an internal PHP implementation if they re not.