Authentication apparatus, method, system and program, and server apparatus

A multi-factor authentication method comprising:

• selecting a security parameter according to a service to be provided to a terminal;
• evaluating a first success probability of an attacker through a first scenario including a combination of procedures of multi-factor authentication;
• comparing the first success probability with the security parameter;
• and
• based on the first success probability exceeding the security parameter, stopping provision of the service through the first scenario to the terminal,
• wherein the method further comprises:
• changing the first scenario to a second scenario including a second combination of procedures of multi-factor authentication so that the first success probability of the attacker through the second scenario becomes lower than the security parameter;
• and
• providing the service to the terminal through the second scenario.

A non-transitory computer-readable recording medium storing a program, the program causing a computer to perform:

• selecting a security parameter according to a service to be provided to a terminal;
• evaluating a first success probability of an attacker through a first scenario including a combination of procedures of multi-factor authentication;
• comparing the first success probability with the security parameter;
• and
• based on the first success probability exceeding the security parameter, stopping provision of the service through the first scenario to the terminal,
• wherein the program further causes the computer perform:
• changing the first scenario to a second scenario including a second combination of procedures of multi-factor authentication so that the first success probability of the attacker through the second scenario becomes lower than the security parameter;
• and
• providing the service to the terminal through the second scenario.