These functions are only available if the interpreter has been compiled with the --with-cybercash=[DIR].
This extension has been removed from PHP as of PHP 4.3.0, if you have questions as to why then you will find the following CyberCash Faq helpful. In short, CyberCash was bought out by VeriSign and although the CyberCash service continues to exist, VeriSign encourages users to switch. See the above faq for details.