Chip and PIN

[ukcrypto@chiark.greenend.org.uk]

Nicholas Bohm wrote:

> The banks have fielded a system that relies on shared secrets.  The fact
> that the secret has been used in an ATM is evidence either that the
> customer used it, or that an insider has purloined the secret from the
> bank, or that a third party has intercepted it (shoulder-surfing, skimmers).

> In an era in which assymetric cryptography makes reliance on shared
> secrets unnecessary, those who field systems that rely on shared secrets
> should not be allowed to claim that use of the secret is proof of use by
> the customer.  That would give them a decent incentive to deploy more
> secure systems.  In the meantime some crooks would get away with fraud.
>  But that seems to me better than leaving the banks and the Ombudsman
> service to exercise a discretion about who they will believe and who
> they will not without any disclosure of any convincing evidence.

I think that's not quite a fair assessment.  The PIN is shared between
the customer's brain and (as I understand it) a pool of HSMs and also
exposed to keyboards in various places of modest security.

Replacement with public key technology might require one of
 - the customer to have incredible mental arithmetic
 - using a key stored on the card; proving possession of the card and not much else
 - replacing the card with a portable computer adequate in both power and security.

Mere existence of assymetric cryptography and making practical use of it with
most of the population are two different things.  But I agree with the need to
restore balance to the adjuducation process.