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Apr
26
comment Can I prove set membership and uniqueness without revealing the element?
@DrLecter, yeah, you definitely have a misconception about commitment schemes. $g^a$ is not a secure commitment to $a$. It is not hiding (neither computationally hiding nor information-theoretically hiding). As a result, it is not classified as a secure commitment scheme. A secure commitment scheme must be both binding and hiding. Therefore, what you are talking about is not a DL commitment -- it's not a commitment at all; it's just a broken thing that doesn't work. Of course, when I mention using a commitment scheme, I assume you use a secure commitment scheme, not something broken.
Apr
25
comment Can I prove set membership and uniqueness without revealing the element?
@DrLecter, I think you have a confusion/misconception about DL commitments. I'm not sure what specifically you have in mind when you mention "DL commitments", but any commitment scheme (whether information-theoretically hiding or computationally hiding) will conceal what was committed to -- nothing is leaked. It doesn't matter whether the value being committed to is low entropy or not; secure commitment schemes promise not to leak what was committed, even if the value has low entropy. If it's not hiding, it's not a secure commitment scheme. For instance, $C(x)=g^x$ isn't secure.
Apr
25
comment Nonlinearity of the J-K Flip Flop
@WilliamHird, I think you might have a misconception. It sounds like you want to design a secure stream cipher, and your approach is to try to find a function that in isolation has some combinatorial properties. This has two problems: (1) to design a secure stream cipher, you need to look holistically at the entire design; you can't just pick out one component/function used in the stream cipher and say that "since it has properties X,Y,Z, the cipher is secure"; (2) designing secure ciphers is very hard, and you're unlikely to do better than existing state-of-the-art schemes.
Apr
21
comment Stateless hash based public key cryptography?
@HenrickHellström, the blog post (the first URL) has some more details. We save only the first level -- that's generated during key generation and treated as part of the private key. We regenerate the subtrees on the fly as needed. How are they generated? They can be generated via a GGM construction from a seed (e.g., computed as a PRF of some master key that's part of the private key, plus an identifier that identifies which subtree we're looking at). There's no need to save the subtrees, since they can be generated deterministically on demand as needed. Does that answer your questions?
Apr
17
comment Is the strength of RSA over quadratic or other cyclotomic fields as strong as over the integers?
Can you explain what you mean by "compose the modulus of some other quadratic ring"? Do you mean that instead of multiplying two integers to get the modulus, we multiply two elements of some quadratic ring? Have you worked out what the corresponding version of Euler's lemma is? What is the order of the multiplicative group of such rings? What's the motivation for your question? Are you hoping to get a cryptosystem that will be faster than RSA, for a given security level?
Apr
16
comment Are there any elliptic curve asymmetric encryption algorithms?
Thanks, DrLecter! Makes sense! On re-reading the question, the question is not as clear as I initially thought. The question says "Is there an algorithm which employs elliptic curve cryptography, fast asymmetric encryption, [...]" - I took that to mean it wants the encryption operation to be fast, like in RSA, but it's entirely possible that might not be the right reading. Perhaps the original author will take a moment to edit the question and make what he/she is looking for clearer.
Apr
16
comment Are there any elliptic curve asymmetric encryption algorithms?
Those are all good schemes, but doesn't the question ask for encryption to be fast like in RSA? Do any of these schemes support encryption that is as fast as RSA's encryption? As far as I can tell, none of them are -- have I misunderstood? I think there's a tradeoff: RSA encryption will be faster than the ECC schemes; the ECC schemes will be faster for everything else, and will have shorter keys.
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).