[messaging] Zero knowledge proofs of passport

[Mike Hearn]

>
>  How does the private secret in passports thing work?


Sorry, just realised I didn't really answer this.

The passport contains an entirely typical NFC capable smartcard chip. The
key is generated inside the chip at some point (typically when it's booted
at the factory) and never leaves. The chip can sign messages with it,
although for reasons that are obscure the current generation of chips has
some bizarre custom hash-based signing method. Probably it's power related.
The tech to allow complex operations like signing using power provided by
an external radio is quite tricky and heavily patented.

The static data then contains the public key, and all the data is signed in
a standard manner by the issuing government.

Thus for passports that support it, it should be possible to hack them into
something like a regular smartcard signing device, accessible via a
smartphone. I have not tried this because my own passport doesn't support
it. It's static only, like most.
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