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Jun
30
revised Associative standard cryptographic hash function
added 1251 characters in body
Jun
30
answered Associative standard cryptographic hash function
Jun
26
awarded  Custodian
Jun
26
reviewed Leave Closed RSA: Common modulus attack problem
Jun
26
comment RSA: Common modulus attack problem
CGFox, rather than editing your question here, it would be better to propose an edit to the answer on the other thread that adds a clarification of how to deal with a negative exponent, i.e., what it means to raise to the $s_1$ power if $s_1$ is negative.
Jun
26
reviewed Leave Open Is HMAC needed for a SHA-3 based MAC?
Jun
26
reviewed Looks OK Testing hardware random number generators?
Jun
25
comment Choose a random number that is different from a bunch of other secret numbers
@CedricMartin, the standard commutative encryption algorithms (e.g., Pohlig-Hellman) do not require a TTP to hold any keys. The prime $p$ is public and shared by everyone; each participant's exponent is secret and is their key and is generated by them and known only to them. No TTP is needed. If you have questions how to use commutative encryption in practice, I suggest reading the existing questions, then posting a new question if it's not covered by the ones that are already on this site.
Jun
25
answered LFSR Output Sampling for Berlekamp-Massey
Jun
25
answered Encrypt-then-MAC: full random keys or keys derived from master key?
Jun
25
comment Choose a random number that is different from a bunch of other secret numbers
@CedricMartin, you are aware that this scheme (from otus) doesn't require a TTP, right?
Jun
25
answered Is it a good idea to use Lagrange/Newtonian interpolation for encryption?
Jun
25
revised Choose a random number that is different from a bunch of other secret numbers
Link to more on commutative encryption.
Jun
25
comment Choose a random number that is different from a bunch of other secret numbers
Very nice! Thank you for elaborating. This looks to me like the best answer I've seen.
Jun
24
reviewed Approve suggested edit on Choose a random number that is different from a bunch of other secret numbers
Jun
24
revised Choose a random number that is different from a bunch of other secret numbers
added 409 characters in body
Jun
24
comment Choose a random number that is different from a bunch of other secret numbers
(...) in the first place, and could we change that procedure? Also, you might want to post a separate question where you take a step back and look at your application's requirements (what problem you want to use this protocol to solve) and ask about how to solve that problem, without assuming this protocol is the best way to do it. I suspect there might be other very different approaches that are possible, but without knowing the application, it's hard for tell.
Jun
24
comment Choose a random number that is different from a bunch of other secret numbers
I've been thinking about this some more, and I think there are a lot of options here. Cedric, can you tell us more? Will this protocol be repeated many times (with the same secret values for the participants), and if so, what are the requirements (a different random number each time, or it's OK for them to repeat) and how many times (more than $x-n$?)? What security property does your application need for the random numbers? Is there a trusted third party? Is there a trusted dealer (a TTP who can provide initial setup/keys)? How did the participants choose their secret values (...)
Jun
24
comment Choose a random number that is different from a bunch of other secret numbers
This is not a great scheme. The problem is that any time a participant vetos a candidate random number, everyone learns what that participant's secret number was (it must have been the same as the candidate random number we were considering). See my answer for a scheme that is a bit better, because it doesn't reveal which participant vetoed the candidate.
Jun
24
answered Choose a random number that is different from a bunch of other secret numbers