It seems he's just talking about technical signature, and not a legal one.
It's a chip, with a hard to extract private key. You give it some input, and you get an output which is the signature of that input signed by that private key. The article isn't talking about whether this signature is legally admissable.
> You give it some input, and you get an output which is the signature of that input signed by that private key.
My point is, this is technically impossible at the moment with German ID documents because using this function requires a commercial certificate which have not been issued since 2017.
It's a chip, with a hard to extract private key. You give it some input, and you get an output which is the signature of that input signed by that private key. The article isn't talking about whether this signature is legally admissable.