Replying to myself here to leave a note:
This mechanism if susceptible to offline attacks, i.e. if an attacker
can sniff the challenge and response messages, he/she can try to brute
force the PIN.
The level of protection offered by this mechanism is directly related
with the strength of the PIN, e.g. a PIN like '1234' would be quickly
cracked - so a strong password should be selected as the PIN. This, of
course, would cause problems with numeric only pinpad readers...
Joao Pedro <[email protected]> wrote:
Hi all,
Recently, I've been wondering about ways to mitigate the problem of
the PINs, in the Muscle applet, being transmitted in clear text from
the terminal to the card. The reason is we are seeing more and more
wireless smart card readers and sniffing is a threat that can not be
dismissed.
A obvious way would be implementing secure messaging and I think one
should look into it, but that solution requires a bigger effort...
So, what do you think about the idea of protecting PINs in the
Muscle applet using keyed hashing, something along the lines of
HMAC-SHA1, or any other derivative. I think that, in a way, the
External Authentication code in the applet is supposed to do this,
but using keys (DES, 3DES, RSA, etc.).
The idea is the following:
If a user wishes to verify its PIN, instead of just using sending a
INS_VERIFY_PIN APDU with the PIN clear text, the following would
happen:
Pre-condition: The card has the PIN stored in clear text.
1. [Terminal] Sends a INS_GET_CHALLENGE message to the card.
2. [Card] Sends a NONCE to the terminal.
3. [Terminal] Computes RT = HMAC-SHA1(PIN, NONCE); sends RT to the card.
4. [Card] Computes RC = HMAC-SHA(PIN, NONCE); RT == RC ? OK : Fail.
What do you think of it? Is it stupid/flawed/insecure/reinventing
the wheel and serves no purpose at all. Or could it be used in real
life?
Thank you.
Regards,
Joao
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