Methods for(作答此空)people differ significantly from those for authenticating machinesand programs,and this is because of the major differences in the capabilitiesof people versuscomputers.Computers are great at doing（ ）calculations quickly and correctly,and theyhave large memories into which they can store and later retrieve Gigabytes of information.Humans don't.So we need to use different methods to authenticate people.In particular,the（ ）protocols we've already discussed are not well suited if the principal beingauthenticated is a person(with all the associated limitations)

All approaches for human authentication rely on at least one ofthe following:

·Something you know (eg.a password).This is the most common kind of authentication usedforhumans.We use passwords every day to access our systems.Unfortunately,somethingthat you know can become something you just forgot.And if you write it down,then otherpeople might find it.Something you（ ）(eg.a smart card).This form of human authentication removes theproblem of forgetting something you know,but some object now must be with you any timeyouwant to be authenticated.And such anobject might be stolen and then becomes somethingthe attacker has

Something you are (eg.a fingerprint).Base authenticationon something （ ）to theprincipal being authenticated.It's much harder to lose a fingerprint than a wallet.Unfortunately,biometricsensors are fairly expensive and(at present)not very accurate.