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Re: Chaffing & winnowing without overhead
By the way, instead of transmitting the first bit for which
MAC(sequence,0) differs from MAC(sequence,1), as Jes�s suggests,
you can get the same effect by transmitting a 0 or 1 depending on
MAC(sequence,0) < MAC(sequence,1)
(This assumes a big-endian system and unsigned comparisons;
little-endians will have to calculate it the hard way.)
If you're willing to be wrong 1 time out of 2**33,
you can just use the top 32 bits.
Earlier in this discussion:
>> In the Rivest's paper you transmit, indeed, all the 2^n plaintexts for a
>> n bit length };-).
>Not so. In his paper (before the package tranform stuff), he had the following expansion.
>Assuming a 32 bit serial number and a 160 bit MAC, n bits would expand to 388n.
>>To make this clearer with an example, note that the adversary
>>will see triples of the form:
>> (1,0,351216)
>> (1,1,895634)
>> (2,0,452412)
>> (2,1,534981)
But that _does send the 2^n plaintexts, which are 0 and 1, and n=1.
Thanks!
Bill
Bill Stewart, [email protected]
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