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Nov
1
revised Hash of multiset of values, which lets me compute the hash of the union
added 55 characters in body
Nov
1
revised Hash of multiset of values, which lets me compute the hash of the union
Oops, I want multisets, not sets.
Nov
1
answered Hash of multiset of values, which lets me compute the hash of the union
Nov
1
asked Hash of multiset of values, which lets me compute the hash of the union
Oct
31
comment Is this hand cipher any more secure than the Vigenère cipher?
We need more information about the key. Is the key a sequence of numbers that are uniformly and independently distributed (each number is uniform of all others)? Is the key re-used for multiple messages? How long is the key? What do you do if the message is longer than the length of available key material? For instance, if the key is a sequence of length 15 (say) for each of the rounds, what do you do if your message is longer than 15 characters long? Do you repeat the key? Do you use a different independent key for each round, or do you use the same in each round?
Oct
28
comment ID-based key exchange protocol with PFS
Alex, (1) in that case your requirement should be that you want an efficient protocol (specify what you want to achieve, not how to achieve it), (2) I very much doubt that signatures make the protocol inefficient. Signatures are fast. I mean, you're OK with the inefficiency of bilinear pairings, but not with ordinary digital signatures? That's counter-intuitive.
Oct
28
comment ID-based key exchange protocol with PFS
What is the reason for your requirement "besides using digital signatures"? What's wrong with using digital signatures? This seems like an odd requirement to impose.
Oct
27
comment ID-based key exchange protocol with PFS
@Alex, you're right, that's an even better scheme. I've added it to my answer. (For future reference, if you already know of a partial answer to your question when asking your question, it would be helpful to include it in the question; that increases the chances that someone can give you a helpful answer.) I've edited my answer, and I believe that everything in my answer is accurate.
Oct
27
revised ID-based key exchange protocol with PFS
added 460 characters in body
Oct
27
revised ID-based key exchange protocol with PFS
added 162 characters in body
Oct
27
comment ID-based key exchange protocol with PFS
@Alex, thanks for your interest. I described a hybrid scheme (which derives ephemeral session keys using DH/ECDH) in the 2nd paragraph of my answer, right after the phrase "hybrid scheme".
Oct
27
answered ID-based key exchange protocol with PFS
Oct
25
comment Hypothetical unknown cipher - security in obscurity?
Your premises are implausible in practice. What if an alien bought a pig at the market, and the pig the alien picked just happened to be able to fly? Hey, it could happen....
Oct
24
comment How do I prove that this PRNG is easily distinguished from a random sequence of numbers (modulo m)?
What have you tried? Where did you get stuck? (We expect you to make some effort before asking here.) Do you know what the definition of "distinguishing from a random sequence" is? Have you tried plugging into the definition? Where did this problem arise? What's the context/motivation? Why do you need to prove it? If it's a textbook exercise, have you reviewed the material on PRGs and on elementary number theory?
Oct
23
comment Should I use the first or last bits from a SHA-256 hash?
@Pacerier - No. There is no reason to believe that using the last bits would be detrimental to security (and there are very strong reasons to expect that it is not detrimental). You're misreading the contents of that link.
Oct
21
comment What's wrong with MARS?
"As I understand only MARS and Serpent implement measures to counter future cryptoanalytic attacks" - Your understanding is faulty. All of the finalists (probably all of the submissions, or essentially all of them) included measures that their designers hoped would counter future cryptanalytic attacks.
Oct
21
comment What's wrong with MARS?
Did you read any of the analysis that was published on MARS? There were a series of workshops with a whole bunch of papers that came out of the proces. Did you read NIST's document explaining their final choice of the AES? If not, those would be good documents to go read!
Oct
21
revised How to verify a number encrypted with an unknown key
Clarify the question. Especially, step 2.
Oct
21
awarded  hash
Oct
20
revised Does encrypting a hash of the message yield a secure MAC?
added 2852 characters in body