Identity disk
From Halopedia, the Halo wiki
An Identity Disk is carried by every Covenant Elite for security purposes. The Identity disk is a small diskette that is meant to be read on a handheld reader. It contains information on its holder, name, rank, etc.
These are not often used, except when utmost formality is at hand, such as when an Elite wishes to meet with Prophets or other members of the High Council. In this case, they are also used in coordination with the DNA slot machines, to ensure the safety of the Prophets and council members.
