PK -> OTP?
Matt Crawford
crawdad at fnal.gov
Mon Mar 14 10:46:04 EST 2005
My educated-layman's opinion is that the following is not feasible, but
I'd be happy to be shown wrong ...
Given a closed public-key device such as a typical smart card with its
limited set of operations (chiefly "sign"), is it possible to implement
a challenge/response function such that
* Both the challenge and the response are short enough for an average
user to be willing to type them when needed.
* The challenge can be generated, and the response verified using the
cardholder's public key and a reasonable amount of computation.
My reasoning is that the full output of the signing function will
almost always be as long as the key, if only response = f(signature) is
given, with f having a range in some set of size ~ 2^32, verifying
response must be nearly as hard as brute-force guessing.
Matt Crawford <crawdad at fnal.gov>
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