These functions are only available if the interpreter has been compiled with the --with-cybercash=[DIR].
This extension has been moved from PHP as of PHP 4.3.0 and now CyberCash lives in PECL.
If you have questions as to the latest status of CyberCash then the following CyberCash Faq will be 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 and PECL link for details.