These CID numbers tend to be used for MAC address randomization and are usually transmitted when a device unassociated with a specific access point broadcasts 802.11 probe requests, the paper explains. CID addresses can be used in situations where global uniqueness is not required. The IEEE also provides the ability to purchase a private OUI that's not associated with a company name, but according to the researchers "this additional privacy feature is not currently used by any major manufacturers that we are aware of."Īlternatively, the IEEE offers a Company Identifier, or CID, which is another three-byte prefix that can be combined with three additional bytes to form 48-bit MAC addresses. The IEEE's registration system makes it easy to identify the maker of a particular piece of network hardware. Put those six bytes together, and you've got a 48-bit MAC address that should be globally unique for each device. Hardware makers can register with the Institute of Electrical and Electronics Engineers (IEEE) to buy a block of MAC addresses for their networking products: the manufacturer is assigned a three-byte Organizationally Unique Identifier, or OUI, with is combined with an additional three-byte identifier that can be set to any value.
Each 802.11 network interface in a mobile phone has a 48-bit MAC address layer-2 hardware identifier, one that's supposed to be persistent and globally unique.
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