|Portable identifiers are physical items that can
associate a digital identity with the bearer.
The earliest portable identifiers were rings, banners, clothes, rarities, and relics. A coat of arms or tartan identified families in some regions. Royalty would have crowns and signets. These items enabled identification even when the face was unfamiliar.
Modern portable identifiers are diverse in form and function. Some are used for generic identification while others enable specific transactions. For example, a credit card is an identifier that is almost exclusively used for purchase. Compare this to a driver’s license, which is used to operate a vehicle, get on an airplane, or provide proof of age.
A portable identifier can be read using visual, contact/ proximity, active broadcasting, and passive scanning techniques:
Visual: Traditional identifiers such as ID cards and state-issued licenses can be visually inspected. This is frequently observed at fine drinking establishments when some burly guy wearing gold chains asks, “Can I see your ID?”
Contact/close proximity: Magnetic and electronic cards such as credit cards and smart cards are read through physical contact—often by “swiping” the card through a reading device. Some magnetic devices can be detected at a short distance, such as when waved in front of a reader.
Active broadcast: Some electronic devices actively broadcast a signal that can be detected by distant receivers. For example, cell phones and some types of auto alarm systems broadcast a locator signal.
Passive scanning: Other electronic identifiers do not have their own power source. External sensors can nonetheless detect these identifiers from a distance. This is useful when contact is impossible or highly impractical. Many major roadways use passive scanning to identify moving vehicles for
the purpose of collecting tolls. A small device mounted on the windshield or kept in the glove compartment is the passive identifier. Implantable passive scan identifiers are now being considered for medical and law-enforcement purposes.
The above information is the start of a chapter in "Network Security Illustrated," published by McGraw-Hill and available from amazon.com, as well as your local bookstore. The book goes into much greater depth on this topic. To learn more about the book and what it covers, click here.
Below, you'll find links to online resources that supplement this portion of the book.