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Jun
25
comment Choose a random number that is different from a bunch of other secret numbers
@CedricMartin, you are aware that this scheme (from otus) doesn't require a TTP, right?
Jun
25
answered Is it a good idea to use Lagrange/Newtonian interpolation for encryption?
Jun
25
revised Choose a random number that is different from a bunch of other secret numbers
Link to more on commutative encryption.
Jun
25
comment Choose a random number that is different from a bunch of other secret numbers
Very nice! Thank you for elaborating. This looks to me like the best answer I've seen.
Jun
24
reviewed Approve suggested edit on Choose a random number that is different from a bunch of other secret numbers
Jun
24
revised Choose a random number that is different from a bunch of other secret numbers
added 409 characters in body
Jun
24
comment Choose a random number that is different from a bunch of other secret numbers
(...) in the first place, and could we change that procedure? Also, you might want to post a separate question where you take a step back and look at your application's requirements (what problem you want to use this protocol to solve) and ask about how to solve that problem, without assuming this protocol is the best way to do it. I suspect there might be other very different approaches that are possible, but without knowing the application, it's hard for tell.
Jun
24
comment Choose a random number that is different from a bunch of other secret numbers
I've been thinking about this some more, and I think there are a lot of options here. Cedric, can you tell us more? Will this protocol be repeated many times (with the same secret values for the participants), and if so, what are the requirements (a different random number each time, or it's OK for them to repeat) and how many times (more than $x-n$?)? What security property does your application need for the random numbers? Is there a trusted third party? Is there a trusted dealer (a TTP who can provide initial setup/keys)? How did the participants choose their secret values (...)
Jun
24
comment Choose a random number that is different from a bunch of other secret numbers
This is not a great scheme. The problem is that any time a participant vetos a candidate random number, everyone learns what that participant's secret number was (it must have been the same as the candidate random number we were considering). See my answer for a scheme that is a bit better, because it doesn't reveal which participant vetoed the candidate.
Jun
24
answered Choose a random number that is different from a bunch of other secret numbers
Jun
24
revised Choose a random number that is different from a bunch of other secret numbers
Incorporate stuff in the comments.
Jun
24
comment Choose a random number that is different from a bunch of other secret numbers
Thanks, nice edit! Here's one more intereseting fact. Proving that two numbers are different can actually be done efficiently, using the proper scheme. See my answer (you use a scheme that is homomorphic for 2-DNF formulas, noticing that $C$ computes a 2-DNF formula).
Jun
24
answered Choose a random number that is different from a bunch of other secret numbers
Jun
24
revised Choose a random number that is different from a bunch of other secret numbers
Remove incorrect statements, to keep only the stuff that'sactually correct.
Jun
23
comment Fastest random number generator
Are you looking for true random numbers, a cryptographic-strength pseudorandom number generator, or a non-cryptographic pseudorandom generator? Please edit the question to state explicitly. Also please edit the question to respond to the other questions in the comments.
Jun
23
comment What would make it impossible to deny that decryption of a package has taken place?
package? What do you mean by that? Do you mean packet?
Jun
23
comment Which concrete applications benefit from Oblivious RAM constructions?
This paper is a great find and very relevant. On the other hand, its threat model makes some assumptions that might not be realistic in practice. It requires that the server know some of the queries (a known-plaintext setting) and have a priori knowledge on some frequency statistics concerning the unencrypted emails. I find it hard to tell whether their attacks will be realistic in the real world or not.
Jun
23
comment how to truncate a PRF on n bits to PRF on t bits where t < n?
Better, in what way? The construction Boneh provides is a perfectly reasonable choice. Unless you can define in what objective metric/criteria you would use to define "better", I don't think this question is well-defined.
Jun
23
answered Cryptography: Oblivious Transfer with at most one transfer?
Jun
23
comment Cryptography: Oblivious Transfer with at most one transfer?
I am finding this question hard to follow. What do you mean by a "transfer method"? What is $Sc$? Do you mean $s_c$? What counts as bits transferred to Bob? Can they invoke $F$ as many times as they want? Who provides the inputs to $F$ (does $x$ come from Alice and $y$ from Bob)? Are we guaranteed that $p,q$ are chosen randomly subject to the condition that $p \oplus q = x \times y$? Please edit the question to make the problem statement clearer.