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The following archive was created by hippie-mail 7.98617-22 on Sat Apr 10 1999 - 01:10:56
David P Jablon (dpj@world.std.com)
Fri, 7 Aug 1998 12:17:25 -0400
Thanks for the clarification -- that the ATM key authenticates
the PIN-MAC on the card.
Your points are well taken, and I agree that offline verification
should be obsolete today.
I should have said that a fixed PIN-MAC key installed in
all ATM's is too-vulnerable to theft or disclosure.
And getting this key (by whatever means) enables a
trivial brute-force attack on every card ever used with
the system. This latter brute-force attack is on the
order of 2^13, the size of a 4-digit PIN, rather than
2^56, or whatever.
Martin Grap wrote:
> Again I am not an ATM expert but the algorithm for the PIN generation/
> verification in the EC system is more or less as follows:
>
> Transform( MAC(key, account number | name | ...) )
>
> where ... refers to other public data on the mag stripe, where the key is
> *not*
> stored on the card and where Transform is a function which maps the MAC
> output to all possible PINs. In a brute force attack you still have to
> try all possible MAC keys. And this brute force attack is hopefully not
> "trivial".
-- dpj
The following archive was created by hippie-mail 7.98617-22 on Sat Apr 10 1999 - 01:10:56