ICAO 9303

In short

ICAO 9303 is the standard that standardizes machine-readable travel documents. It's published by the International Civil Aviation Organization (ICAO), the United Nations specialized agency for civil aviation, and it's also known as Doc 9303.

Its purpose is for a travel document issued by any state to be read and processed by any other with a common procedure. To that end it sets the document's physical format, the location and structure of the data, the machine-readable zone and, on documents with a chip, how the electronic information is stored and protected.

That the standard comes from civil aviation isn't a historical curiosity: the original problem was border migration control, where documents from any country have to be processed in a few seconds.

What the standard standardizes

Its scope is broader than the name suggests, and it can be organized into four layers.

• The physical medium — the document's dimensions and general layout. That's where the designations TD1, TD2 and TD3 come from, which identify document sizes: the card format, the intermediate format and the passport booklet format.
• The printed data — which fields the data page carries, in what order and with what encoding, including the transliteration of names into a common character set.
• The machine-readable zone — the structure of the MRZ: how many lines, how many characters, which field occupies each position and how the check digits are calculated.
• The electronic document — how the data is organized inside the chip, how the issuing authority signs it, and what mechanisms control access to that information.

The standard is published in parts: some cover specifications common to all documents, others each particular format, and others the electronic part and its security mechanisms. It's an extensive technical body, not a single document.

What an eMRTD is

MRTD stands for machine readable travel document. The e in front marks the variant that includes a contactless chip.

The distinction matters because it changes the nature of what can be checked.

An MRTD without a chip is a printed document with a machine-readable zone. Its content is read reliably and its authenticity is assessed through the medium's security features.

An eMRTD adds a chip whose content is signed by the issuing authority. That signature is verified against the certificate of the country that produced it, and the check stops depending on visual assessment. The standard also defines mechanisms that prevent the chip from being read without the physical document present, and ones aimed at detecting a cloned chip.

It's why the same body of standards covers two generations of documents that in practice are verified in very different ways.

Why an aviation standard reached national ID cards

A passport is a travel document and the standard applies to it by definition. A national ID card, in principle, doesn't.

Even so, the TD1 format spread to documents never meant to cross a border. The reason is practical: a state that issues a document with the standard's structure gets, without developing anything of its own, a data format any reader in the world already knows how to interpret, and a check-digit scheme proven over decades.

For whoever builds a verification process, the effect is concrete. A national document that follows the standard is read with the same routine as a passport. One that doesn't requires learning its particular layout, its data format and its validation rules, one by one.

That explains an asymmetry that tends to surprise: reading a passport from a faraway country well can be simpler than reading an older version of the neighboring country's ID card well.

What the standard doesn't cover

Defining its limits avoids the most common confusion, which is reading it as a quality seal for a verification process.

• It doesn't certify vendors or processes. It's a document specification. No organization "complies with ICAO 9303": documents follow it, and systems implement it.
• It says nothing about live facial biometrics. The eMRTD stores a facial image of the holder, but checking that whoever presents the document is a real person present is a different problem, with its own standards and its own tests.
• It doesn't cover the [barcode](/glosario/pdf417) on the back. The codes many ID cards and licenses in the region carry on the back follow other standards and issuer decisions.
• It doesn't resolve the document's validity. That a document is well-formed under the standard doesn't say whether it was revoked, reported or canceled. That's answered against an official source, wherever the country exposes one.