Encryption of data in smart cards

[Anne & Lynn Wheeler]

At 01:13 PM 3/13/2003 -0500, John Kelsey wrote:
>At 11:08 PM 3/12/03 +0100, Krister Walfridsson wrote:
>
>...
>>This is not completely true -- I have seen some high-end cards that use
>>the PIN code entered by the user as the encryption key.  And it is quite
>>easy to do similar things on Java cards...
>
>With any kind of reasonable PIN length, though, this isn't all that 
>helpful, because of the small set of possible PINs.  And smartcards don't 
>generally have a lot of processing power, so making the PIN->key mapping 
>expensive doesn't help much, either.
>
>>    /Krister
>
>--John Kelsey, kelsey.j at ix.netcom.com

note however, that PIN could be possibly in infrastructure with real secret 
key and encryption done with derived key. the derived key one-way function 
is attempting to protect the infrastructure-wide secret key from brute 
force key search on specific piece of data. The issue is how many bits in a 
PIN is required to protect the secret key in a one-way function (involving 
the secret key and the PIN). A simple derived key is sufficient using the 
secret key and public account number. Adding a (privately known, card 
specific) PIN to such a derived key function:

1) doesn't increase the ease of attack on the secret key

2) doesn't affect brute force attack on the derived key

3) makes it harder to use a lost/stolen card
--
Anne & Lynn Wheeler    http://www.garlic.com/~lynn/
Internet trivia 20th anv http://www.garlic.com/~lynn/rfcietff.htm
  


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