Electronic machine readable travel document (eMRTD)

The signed chip in a passport or ID card: passive authentication, chip authentication and PACE, and why reading it beats photographing a document.

A travel or identity document with a contactless chip, specified in ICAO Doc 9303. The chip holds the data that are printed on the document - the machine readable zone, the facial image and other data groups - and, crucially, a signature over those data made by the issuing country.

The security comes in layers. Passive authentication verifies that signature: the country's signing certificate signs document signer certificates, which sign the data on each chip, so a verifier can establish that the content was issued by that country and has not been altered - an ordinary certificate chain in an unusual place. Chip authentication proves that the chip itself is genuine rather than a copy of somebody else's data, which is what passive authentication alone cannot do. And access control, BAC and its successor PACE, means a reader must first derive a key from data you can only get by holding the document, so the chip does not answer a stranger's radio in your pocket. Of those two, only PACE has a future: ICAO is retiring BAC, requiring states to support PACE from 2027 and to stop issuing BAC-only documents the year after, with the last legacy documents out of circulation in the 2030s. Build for PACE, keep reading BAC for as long as old passports are in wallets.

For remote identity verification this is the difference between reading a document and photographing one. A picture can be a picture of a picture; a chip read over NFC yields data signed by a state. Combined with biometric liveness detection, which binds that document to the person present, it is the route to onboarding at assurance level high without a counter - and the reason the Cleverbase app asks you to hold your phone against your passport instead of sending a scan.