Cryptography from sunspots: How to use an imperfect string
Speaker: Abhi Shelat , University of Virginia
Date: October 12 2007
Time: 10:30AM to 12:00PM
Location: Patil/Kiva 32-G449
Host: Prof Silvio Micali, MIT
Contact: Chuck Wright, 617-253-6025, chuck@csail.mit.edu
Relevant URL: >> The Common Reference String (CRS) model enables otherwise-impossible cryptographic goals such as removing interaction from protocols and guaranteeing composable security. However, the CRS model requires the reference string to be sampled from a fixed and known distribution (e.g., the uniform distribution); security analyses of all current protocols fail when the actual distribution of the reference string differs from the specified one even by a small amount.
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>> This fact rules out a large class of potential implementations of the CRS model such as measurements of physical phenomena (like sunspots), or alternatively using random sources that might be adversarially influenced.
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>> We study the possibility of obtaining universally composable (UC) security in a relaxed variant of theCRS model in which the reference string it sampled from an *arbitrary, adversarially specified* distribution that is unknown to the protocol. On the positive side, we demonstrate that UC general secure computation is obtainable in this model as long as:
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>> (a) this distribution has some minimal min-entropy,
>> (b) it is efficiently samplable,
>> (c) the sampling algorithm has not too long a description, and
>> (d) the sampling algorithm is known to the adversary (and simulator).
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>> On the negative side, we show that if any one of these four conditions is removed then general UC secure computation becomes impossible.
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