a portable personal identification card allows a cardholder to enter a pin code into his card at a location remote from an authorization terminal . in an alternate embodiment , a pin code may be enterd at the authorization terminal . the authorization terminal reads the cardholder &# 39 ; s account number from the pin card . the account number is transmitted to a central computer which uses this number to index into memory to find a personal identification number and encryption parameters . the centerl computer transmits a pseudo - random number to the pin card . both the pin card and the central computer perform an encryption of a function of the corresponding personal indentification number and pseudo - random number to derive a cgipin . if the cgipin transmitted from the pin card matches the cgipin of the central computer , access is authorized .