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Feb
24
comment $f : \mathbb{Z}_n \rightarrow \mathbb{Z}^\times_n$?
Please clarify your question. As it stands, your parenthesis does not correspond to any notion of inversion that I am familiar with. Also please define your notation, e.g., the $\mathbb{Z}_n^\times$ notation. And why is this a cryptography question? Please add some context or motivation, and tell us what you've tried to do on your understand to figure out the answer for yourself. Have you reviewed standard material on modular arithmetic?
Feb
24
comment Seed / reseed DRBG too often?
rzetterberg, for most applications (if you can reseed), the advice in your library documentation is undoubtedly good advice. But for many DRBG's, that advice is probably more cautious than is really necessary. Therefore, if there's some reason why you can't re-seed, don't take that advice as gospel: do a risk analysis to see if it's really necessary.
Feb
21
comment Homomorphic crypto allowing anonymous yes/no votes?
Are you aware that there is tons of work on secure voting schemes? Probably hundreds of papers. Have you done a search on this site and a literature search in the literature? Are you familiar with E2E (end-to-end) cryptographic voting systems? For instance, Helios and VoteBox? That would be a good starting point for you.
Feb
21
comment Compared to GCM or XTS modes, how secure is H xor R1, E (R2, R1, Message) for confidentiality and integrity?
@poncho, I took a second look, and you are right. I updated my message accordingly. The bottom line is still the same, though: I can't see any reason to use this scheme.
Feb
21
comment Practical usage of S/KEY
You know that S/KEY and OTP have serious problems if they are used on their own (e.g., over an insecure channel, or if the user does not carefully check who they are authenticating to every time), right? That might be why you haven't heard of much deployed use of it.
Feb
21
comment Seed / reseed DRBG too often?
Actually, the premise that you need to reseed periodically ain't necessarily so. Some documents might suggest that reseeding is mandatory, but if you choose a good DBRG, it's not strictly necessary. The decision of whether to reseed should be based upon a thoughtful risk analysis, not just a blind rule-based "the standard says I have to reseed so I guess I have to".
Feb
21
comment Is there a “brainwallet” for GPG keys?
@RobKohr, you might personally think that password quality not a problem.... but in practice, it is a problem. A 5-word passphrase might have entropy as low as 50 bits or lower. That's not enough to resist off-line attack and would have security problems if you faced a serious motivated adversary.
Feb
18
comment Proving that a function is not a OWF (One-way-function)
@Pinocchio, yes, for a random $x$. Yes, my answer does not depend upon how $f$ is constructed; it applies regardless.
Feb
18
comment Proof of work for standard computers
Two candidates come to mind. (1) Find an input to scrypt that makes the first 20 bits of its output all zeros. Verification is now pretty cheap. (2) Use timelock puzzles. They admit a very large ratio between the time to solve the puzzle vs the time to construct the puzzle (or to verify the solution).
Feb
16
comment Known vulnerabilities in (EC-)KCDSA
jimmy, Have you done a literature search? That's the obvious first step.
Feb
16
comment ML/NN Cryptanalysis
My advice would be to stick to one question per question. Here you have 3 separate question, all concatenated into the same question box. That isn't a good fit for this site; a good question should have a single answer. (Actually, the 3rd one -- "any other tricks..." -- is also not a good fit, as it is too unfocused.) Also, we expect you to do some research on your own and tell us what you've tried; I don't see that in the question at present. Finally, I suggest starting from the goal (drive in a nail) and ask for a solution, rather than starting with a hammer and looking for nails.
Feb
16
comment Where can I find source code of a compiler that secures a circuit (or attemps to)?
Others have expressed the view that requests for implementations are off-topic on this site. See meta.crypto.stackexchange.com/q/191/351.
Feb
12
comment Proof of work for standard computers
Can you please disclose your relationship to Cuckoo Cycle in the answer, to comply with site standards about this? Thank you.
Feb
8
comment Generating Diffie-Hellman parameters efficiently
Right on, @RickyDemer -- thank you! Fixed.
Feb
7
comment Help in understanding exactly how lattices used as one way functions for hashing
you wrote "I just wish I could find some text which explained this in English rather than symbols". I'm afraid you're not likely to be able to understand this without mathematics (i.e., symbols). I don't mean to be rude, but you might want to consider the possibility that you do not have the necessary mathematical background to understand the answers to the questions you posed. Perhaps you are better off either focusing on strengthening your math skills, or moving to a different topic where you do have the preparation.
Feb
6
comment Homomorphic encryption for vector addition
$p$ could be something like $2^{32}$... but depending upon the scheme, it might also be something like a large prime number. Different schemes will be able to support different values for $p,q,r$. So, if you want us to propose a scheme, you'll need to tell us whether you have any specific requirements on what kinds of values of $p,q,r$ will work for you. If there are any combinations of $p,q,r$ that won't work for you, tell us that. If you absolutely must have wraparound occur at $p=q=r=2^{32}$ for all three components, tell us that. etc.
Feb
6
comment Homomorphic encryption for vector addition
@uosɐſ, as you correctly anticipated, the integer arithmetic is going to wrap around eventually: keep incrementing, and eventually you'll get back to zero. This is pretty much inevitable, especially since we're working with modular arithmetic. $p$ is the number where wrap-around happens for the first component. Take $\langle 1,0,0 \rangle$ and keep adding it to itself. You'll get $\langle 2,0,0 \rangle$, $\langle 3,0,0 \rangle$, etc. until $\langle p-1,0,0 \rangle$: then when you add one, it wraps around to $\langle 0,0,0 \rangle$. Similarly, $q,r$ are the modulus for the 2nd/3rd component.
Feb
5
comment Practical (and secure) PRGs
Good point, @user4982! Thank you -- I have edited my answer accordingly.
Feb
4
comment Hill cipher is not perfectly secure
@Valtteri, well done!
Feb
4
comment Game with symmetric key
What do you think? What have you tried? We prefer you to make an effort on your own before asking. This is a nice exercise, but we're not here to solve your exercises for you -- on the other hand, if you have a specific question about a specific aspect of your attempt at a solution, that might be more suitable for this site.