I read this article, but seems like any information about it is kind a omited.
Source: I have been working on a blockchain implementation in the past that was compatible with the cryptographic functions in an NFC passport. Basically using a standard NFC passport as a cold wallet.
Fun fact. The cryptographic system even differs per country.
E.g. the Dutch don't trust the NIST elliptic curves so use the brainpool curves instead. Some other countries are still using RSA iirc.
Actual validation methods would be actually cool to read about. Since if we ignore legal diffuculties of storing the data then we can actually use passport cryptography as something like actual proof-of-human without pesky 3rd-parties.
Even then, authorization is completely missing from the ICAO model – it's for authentication of identity documents only. It's explicitly not intended for "proof of humanity", since that requires authorization too, or it'd be vulnerable to any attacker that can briefly tap your identity document with their phone.
That's one of the reasons why active authentication was deprecated, presumably: Signatures without document owner authorization can be misleading/interpreted as confirming intent, not just document existence.
It won't help with that at all, since without requiring active involvement of some credential or trusted party, all there is is a static signature saying "there's a person called $name born on $dob", but nothing saying "and that person wants to <send an email|register an account|...>".
There is a way to use ICAO documents supporting "Active Authentication" in such a way, and I've seen proofs of concept leveraging it, but it was an unintentional consequence of using RSA signatures for authentication and fixed/removed in newer cards.