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Jan
23
comment Hiding and Binding key in Groth-Sahai NIZK proof system
Please don't use images as the main content of your post. It's not accessible to the visually impaired and it's not indexed via search.
Jan
17
awarded  Guru
Jan
15
comment Formal security of recycled random blinding in a Paillier scheme
@Dave, for a fixed subset of the $R$'s, the chances of a collision are the same. Now count the number of such subsets. You'll find that there are exponentially many subsets, so once you sign a reasonably large number of messages, the probability that there exists some such multiplicative relationship is close to 1.
Jan
15
revised Formal security of recycled random blinding in a Paillier scheme
added 677 characters in body
Jan
15
comment Formal security of recycled random blinding in a Paillier scheme
@Dave, I think some of your details are a bit off there: there's no reason that $R_a R_b = R_c R_d$ would require $a+b=c+d$.
Jan
15
comment Possible to use an accumulator to “license” or restrict the qty of certificates being used?
This might not be obvious, but the way this site works is that we expect all requirements to be in the question. This is not a discussion forum. Comments exist only to help you improve the question/the answer, and can disappear at any time. If you've worked out that the question needs to be revised/refined, you should edit the question accordingly -- and the same goes for your answer. Again, it's not a discussion forum, and readers shouldn't have to dive into some discussion in the comments to understand what the question is.
Jan
15
comment Possible to use an accumulator to “license” or restrict the qty of certificates being used?
Understood. But as I wrote... "that isn't quite what the question asked for". The question asked us to prevent issuing more than $n$ certificates. The answer doesn't mention this caveat. If the answer proposes a scheme that achieves something less than what was asked for, and where it might not be obvious that this is the case, it would be helpful to explain the limitations, describe what properties it does achieve, and explore whether the resulting scheme might still be adequate in practice or not. I suspect some child CA's might potentially be OK with their private key leaking.
Jan
15
comment Integrity protection in wireless sensor networks
For the future: 1. One question per question please. This site format doesn't work so well when you have a bunch of different questions stuffed together. 2. Please do more research before asking. We expect you to do a significant amount of research and self-study. Many of your questions are already answered in standard resources (textbooks, online resources, other questions on this site).
Jan
15
comment Possible to use an accumulator to “license” or restrict the qty of certificates being used?
This proposed solution doesn't work. A signer can still re-use the nonce to sign multiple messages. Therefore, this scheme doesn't prevent a child CA from issuing more than the allowed number of certificates. (Of course, if the child CA does issue more than the allowed number of signatures, it might allow others to forge signatures that look like they came from the child CA, so it might have some negative consequences for the child CA, but that's a bit delicate and isn't quite what the question asked for.)
Jan
14
comment Possible to use an accumulator to “license” or restrict the qty of certificates being used?
This answer doesn't work. I think you are confused about what a $n$-time signature scheme is. A $n$-time signature scheme is a signature scheme that is secure as long as it is used only $n$ times. There is no guarantee that it's impossible to sign $n+1$ messages, and indeed every $n$-time signature scheme I've ever seen does allow signer to sign $n+1$ messages if he wishes (though this could enable others to forge additional signatures).
Jan
14
answered Formal security of recycled random blinding in a Paillier scheme
Jan
14
reviewed Approve TimeStamp in Cache-time attacks on AES
Jan
14
comment TimeStamp in Cache-time attacks on AES
This question appears to be off-topic because it is about the meaning of Intel x86 assembly instructions; this site is for questions about cryptography.
Jan
13
comment Automated testing of cipher security for import/export compliance
@TruthSerum, I still don't get it. In what sense does my answer not answer your question? Everything I wrote still applies. No, there is no known way to automatically test and grade the security of an arbitrary cipher. That's not how we do it in practice. Perhaps if you elaborate the question it will become clearer what you are looking for and/or why you think this doesn't answer the question?
Jan
13
comment Automated testing of cipher security for import/export compliance
@TruthSerum, you didn't state that in the question. Please edit your question, and this time make sure all relevant information is included in the question. Actually, I'm finding it difficult to guess exactly what you are asking or looking for. This is starting to look like a "chameleon question" (one that changes each time someone adds an answer); that's discouraged on this site and may discourage people from answering.
Jan
13
answered Automated testing of cipher security for import/export compliance
Jan
6
comment (Re-)Using deterministic IV in CTR mode / How to: deterministic AES
@SebastianS, if you have requirements on how much expansion is allowed (how much longer the ciphertext can be than the plaintext), then state that in the quesiton. Don't assume that convergent encryption cannot meet those requirements; there are certainly convergent encryption schemes with relatively small expansion. Nothing forces you to have 256 bits of expansion. Don't judge all of convergent encryption by one particular scheme with one particular set of parameters.
Jan
6
revised Is a Combined Linear Congruential Generator secure for cryptography?
added 84 characters in body
Jan
6
comment Is a Combined Linear Congruential Generator secure for cryptography?
See crypto.stackexchange.com/q/21212/351 for a general answer to this question..
Jan
6
answered Why is the private key generated first in public key crypto?