Credential--信任状

A credential is
something you know, such as number or PIN;
something you have, such as an access badge;
something you are, such as a biometric feature;
or some combination of these.

The typical credential is an access card, key fob, or other key.
There are many card technologies including magnetic stripe, bar code, Wiegand, 125 kHz proximity, 26 bit card-swipe, contact smart cards, and contactless smart cards.
Also available are key-fobs which are more compact than ID cards and attach to a key ring.
Typical biometric technologies include fingerprint, facial recognition, iris recognition, retinal scan, voice, and hand geometry.

ref: Access control wikipedia http://en.wikipedia.org/wiki/Access_control