[pas]

... information theoretically... you can't

it's okay

there's already some fraud, waste, loss, inefficiencies, accidents (packages lost, chargebacks by mistake, package arrives weeks later)

....

that said the chips have some physical protection, it's not trivial to clone them

and the chip has a variable where it stores how much more you can use without online confirmation

of course, these are cheap protective measures, but to crack it you would need more effort probably than the total credit that's assigned for offline spending

[lxgr]

What's the information theory connection in your view?

> these are cheap protective measures,

They're holding up extremely well. I'm not aware of any cryptographic or physical key extraction compromise in EMV, for example. All known bugs are protocol design oopsies, as far as I'm aware.

[pas]

since the key is there it's not impossible to extract it in theory