20,702 reputation
32574
bio website
location
age
visits member for 3 years, 3 months
seen 2 days ago

Dec
6
comment Slow one-way pseudo-random permutation?
Also, why does your application require such a complex construct? Why not just store a unique random serial number in the 2-D barcode, and have a back-end database that maps the serial number to whatever data is associated to that card (of course, the data can be encrypted under one merchant's key if you wish). Perhaps I haven't quite understood the application yet.
Dec
6
comment Slow one-way pseudo-random permutation?
Why do you need the output to be the same length as the input? If you're willing to have (say) a 256-bit output, your goals are easy to achieve; just use the SHA256 hash. If the output is going to be stored in a database but not stored on the card, that'd suffice. Also, why do you need it to be bijective (i.e., a permutation)? If collisions are non-trivial to find, is that good enough?
Dec
6
comment Enhance CSPRNG output
@user1028028, it doesn't matter if the PRNGs are independent. What matters is that their seeds (their keys) are independently chosen. That's how you can tell: check how you've generated them.
Dec
6
comment Enhance CSPRNG output
"Unrelated" is NOT the criterion. The criterion is that the keys be independently chosen, not that the algorithms be "unrelated" or "independent" (whatever that would mean). You can even use the same CSPRNG algorithm, as long as you have two independent keys.
Dec
6
comment Enhance CSPRNG output
How are they keyed? With two independent keys? Also, if one is a CSPRNG, then it cannot be biased (to be cryptographically secure means that it can't be biased).
Dec
6
comment If H(m) = 0 for some m, how can a DSA signature be forged?
As DrLecter says, when asking this sort of question, please make sure to describe what you've tried and where you got stuck. We expect you to make a serious effort before asking here and to show us what you've tried and where you got stuck.
Dec
6
comment Is an elliptic curve over $\mathbb{F}_p$ order preserving for the points $(x,y) \in \mathbb{Z}_p$?
Could you define what you mean by $E(x)=y$? If $E$ is the curve, then $E(x)$ is not well-defined. Do you mean $x,y$ such that $(x,y)$ is on the curve (i.e., $y^2=x^3+ax+b \pmod p$)?
Dec
6
comment Is there any analysis of freebsd's “geli” encrypted geometry provider?
Got any suggested links for reading about how geli works and how its crypto works? Any overviews or other resources that you think might be a helpful place to start for those who might want to start taking a look at it? If yes, that might be worth editing into your question.
Dec
4
comment Who uses Dual_EC_DRBG?
That patent does not appear to patent Dual_EC_DBRG. Nor does it appear to patent any backdoor. Rather, the patent lists Dual_EC_DBRG in the prior art, and claims to patent a method for generating the points P,Q in a way that is verifiably free of backdoors.
Nov
20
comment How to prove this LFSR equation?
I suggest you edit the question to include that information, to make this question self-contained, as well as to define the notation $(f,g)$ and $[f,g]$ for polynomials and $+$ for solution spaces. Also, I suggest you edit the question to show what you've tried so far and where you got stuck.
Nov
18
comment Should we sign-then-encrypt, or encrypt-then-sign?
@louism, that's a separate question. This isn't a discussion forum -- questions should be posted separately (see the Ask Question on the upper right). But make sure to first read the help center, and do your research (try to answer the question on your own using Google, Wikipedia, search on this site, etc.) before asking.
Nov
17
comment Bellovin 96' attack on IPsec ESP protocol on encryption only option
Did you read the description in the paper carefully, one step at a time? Where did you get lost? Are you familiar with other attacks on modes of operation?
Nov
16
comment Homomorphic (encrypted) comparison to an integer
OK, much better! Now I believe that this should work. +1. Thank you for your patience with all my questions and doubts.
Nov
14
comment Has threefish successfully been attacked (practically or theoretically)?
What research have you done? Have you done a literature search? We expect you to make some effort to find out the answer on your own before asking, and to show what you've tried so far.
Nov
10
comment Perfect Forward Secrecy in MTI/A0
I encourage you to define the terminology you use (e.g., MTI/A0, LL-key), as I'm not familiar to them. Also, if you have a link to the paper(s) that introduce this scheme, I encourage you to post them. This might increase the chances that you get a good answer.
Nov
9
comment Why is it important to generate a pseudorandom permutation from a pseudorandom function?
What do you mean by "it is important [to do it this way]" or "it is necessary [to do it this way]"? I think you have a misconception/erroneous premise. This is one popular way to build a block cipher, but it's not the only way. It is neither necessary nor important to construct the block cipher this way. There are other ways to construct secure ciphers; see, e.g., AES/Rijndael.
Nov
7
comment partial-domain permutation and strong assumption
Did you read the cited paper on OAEP? I would expect that it's likely to have a definition of those terms.
Nov
7
comment What aspects of information theory are used in modern cryptography?
I suspect this is too broad to be a good fit for this site: you could probably write a whole book about it. (Also, the answer depends on what you mean by a "working cryptographer".)
Nov
7
comment Are there any bijective one-way functions not based on number-theoretic hardness assumptions?
The term you are looking for is "one-way permutation". There are many candidate constructions. Why would you insist that you are not willing to rely upon number-theoretic hardness assertions? That seems unnecessarily limiting and not well motivated.
Nov
5
comment Is this hand cipher any more secure than the Vigenère cipher?
user54609, I asked about 7 different questions, and you answered about 4 of them. Still wondering about the other 3.... If you're not going to answer requests for clarification, how do you expect to get a good answer? Seems odd to place a bounty but not answer such questions. You should also be editing the question to include these clarifications in the question, so people don't need to read the comment thread. P.S. You might also want to notify me when responding, by including "@D.W." in your response.