A cryptographic communication method between IC cards in an electronic ticket distribution system is provided, wherein when a server and a user terminal, to each of which an IC card is connected, begin mutual data-communication or when an IC card and, a ticket collecting machine begin mutual data-communication, they both dynamically change encryption algorithms for mutual authentication and for concealment of contents to be transmitted in accordance with information about commonly usable encryption algorithms exchanged at the beginning of a mutual authentication between them, and this procedure at the beginning of the mutual authentication can result in a speedy and secured cryptographic communication between them.