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Apr
14
comment In Pedersen Key Distribution, can the public key be persistent?
Are you saying there is an attack if you re-use $(p,g,h)$ too many times? Are you saying that existing proofs don't make any promises if you re-use $(p,g,h)$ too many times? Can you give some intuition for what the nature of the alleged trouble is? I find it hard to believe that there is a real problem. It is bog-standard to re-use the public key $(p,g,h)$ in discrete-log-based cryptosystems; is there any reason that Pederson would be different?
Apr
7
comment How could Fully Homomorphic Encryption support power operations?
My perspective: The answer says that XOR and AND are universal, and thus any operation, including addition and multiplication, can be built out of XOR and AND gates. That is a correct statement. So the answer seems fine to me. But we can agree to disagree (or have a slightly different reaction) -- nothing wrong with that!
Apr
7
comment How could Fully Homomorphic Encryption support power operations?
@poncho, I don't understand your comment. This answer looks correct to me. The answer never says "ADD==XOR", does it? XOR and AND are universal; no need for NAND.
Apr
7
comment How could Fully Homomorphic Encryption support power operations?
You already answered your own question. "It enables arbitrary functions..." Power is a function.
Apr
7
comment Is it possible to determine or estimate the period for Blum-Micali PRG?
The premise seems faulty. Cycles can occur even if there is no fixed point. So, focusing on fixed points seems mis-placed, if you really care about cycles. But, as I explain in my answer, worrying about short cycles is also mis-placed concern.
Apr
6
comment Wrong Test Vector for HKDF with HMAC-SHA256
This question appears to be off-topic because it is about software development (try StackOverflow).
Apr
5
comment Should we MAC-then-encrypt or encrypt-then-MAC?
I edited the answer to more clearly express the point Josef was trying to make. Personally, I think the answer is fine (I upvoted it).
Apr
3
comment Key-dependent encryption in TAHOE-LAFS
What is ENC, specifically? How is it instantiated?
Apr
2
comment Combining multiple symmetric encryption algorithms - implications?
@StephenTouset, oh, right, thank you! Boy that was a dumb thing to write. :-) I appreciate the comment.
Mar
31
comment Can a commutative block cipher be indistinguishable from a random permutation, for fixed key?
@fgrieu, yes, maybe posting a separate question would be best. When you do, can you spell out how we choose a random set of permutations with the commutativity property? Is that notion uniquely defined?
Mar
30
comment HKDF vs TLS PRF. Which of the one is better?
Better, in what sense? More secure, in what sense? For what purposes? Under what threat model? This question is too vague as it stands; I suggest you edit it to make it more specific.
Mar
29
comment Is Porticor's “homomorphic” key encryption something that can really be done or is it just marketing hype?
Can you edit your answer to provide a summary of the contents of those documents and their implications for the answer to the question that was asked here? As it stands, the main content of your answer is the links, but on this site we tend not to like link-only answers very much, because links may rot or disappear.
Mar
28
comment Is substitution with random prefix codes secure?
@Mok-KongShen, that's of course a different question, and of course the answer to that question will probably depend on the details. This is not a discussion forum: one question per question, please (so it's important to make sure that you frame your question well so it reflects what you really want answered).
Mar
28
comment What might be assumed about a PRF if the key has been chosen?
I'm confused by "what might be assumed about..." -- you can of course assume anything you want. Do you mean, assuming only that $f$ is a PRF, what can we say about security if the key parameter is not chosen randomly? If so, the answer is: there are no guarantees whatsoever. There are bad cases where the function $f$ is no good at all, if the key is predictable or has low entropy. In TLS, the spec calls the function a PRF, but actually the protocol implicitly requires stronger assumptions than just that it's a PRF; it also needs to have some hash-like properties as well.
Mar
28
comment ECDSA signature verifiable 1-way transformations
@ChristopheBiocca, you can turn any interactive ZKPoK into a non-interactive ZKPoK using the Fiat-Shamir heuristic (basically, use a hash function to choose the challenge). That should give you what you want.
Mar
28
comment Distinguishing Attack on CBC-MACs
@user11291, read fgrieu's earlier comment, and do some learning on your own about the birthday paradox.
Mar
28
comment secure integer comparison
@ahmed, alas, I don't know of a reference for this protocol, and unfortunately I don't know anything better -- sorry about that -- but if you want to explore further, it might be worth taking a look at the protocol I mention in the last paragraph.
Mar
22
comment Is PKCS #1 v1.5 RSA encryption padding secure under these conditions?
Your statement "Alice cannot know if Bob accepted the message" does not seem to be well-justified (at least, it does not follow from the rest of your conditions).
Mar
21
comment Parallel-resistant proof-of-work scheme without hidden knowledge
Thanks, that helps! For randomized schemes, can't you always make them deterministic by seeding a deterministic PRNG with some seed and using its output everywhere that the algorithm makes a random choice? Now the problem/puzzle generated will be a deterministic function of the seed: the same seed always yields the same puzzle. Does that achieve what you're looking for or does it fall short in some way?
Mar
21
comment Is this approach to generating a “random” number from a sha512 hash effective?
Good answer! I'd also like to refer the author to crypto.stackexchange.com/q/767/351.