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Jun
7
comment Obfuscate an “I'll reveal if you do” function
Thank you! Yes, I do have an a-priori bound on the length of $x$ and $y$, so that removes one possible complication. It would be fine to use any commitment scheme that makes the obfuscation task easy, so if Merkle tree based commitments make obfuscation easier, that would be fine.
Jun
6
asked Obfuscate an “I'll reveal if you do” function
Jun
6
comment Attack on a key-exchange,symmetric-key cryptography protocol
I don't understand this answer yet. Are you thinking of gathering this information for all possible values of the nonce? Normally, nonces are chosen to be from a large enough space that such an attack will be wildly impossible: e.g., a nonce might be a random 128-bit number. Would you like to try editing your answer to clarify what attack you had in mind and what security property is violated by your attack?
Jun
5
revised Three different numbers with x³=x mod p
added 49 characters in body
Jun
5
revised Security of a security protocol for key exchange, using symmetric-key cryptography
rolled back to a previous revision
Jun
5
comment Universal Circuits in Indistinguishability Obfuscation Candidate Construction
I don't know. Maybe the security proof requires use of the universal circuit? (e.g., to ensure the branching program will have the same structure regardless of what the original circuit is, or something)
Jun
3
comment Theory for pre-paid debit card: card-to-card transfer
That's one kind of approach. The other kind is to use a coin-based scheme for e-cash, e.g., Chaum-style e-cash (based upon blind signatures).
Jun
3
answered Theory for pre-paid debit card: card-to-card transfer
Jun
3
comment Theory for pre-paid debit card: card-to-card transfer
What research have you done?
Jun
3
revised Security of a security protocol for key exchange, using symmetric-key cryptography
Choose a more specific title.
Jun
2
answered Use additional keys to thwart key compromise?
Jun
2
comment Which one of the Block Cipher modes is the best?
There is no "best". Best for what purpose? They have different characteristics. Those characteristics are well-documented.
Jun
2
answered Encryption of log files
Jun
2
comment Security of a security protocol for key exchange, using symmetric-key cryptography
Have you tried using an automated protocol analyzer, like AVISPA, ProVerif, CryptoVerif, Scyther, Tamarin, EasyCrypt, CertiCrypt, Maude-NPA, etc.?
Jun
2
revised Reductionist proofs of decisional problems to computational
added 217 characters in body
Jun
2
answered Update to “Cryptographic Right Answers”
Jun
2
comment Why is plain-hash-then-encrypt not a secure MAC?
@IlmariKaronen, Good point! This is worth considering and discussing. Looks like there are many possibilities. Another possibility that might make even more sense would be to close this question as a dup of crypto.stackexchange.com/q/6069/351, since they are both specifically about stream ciphers. (I do not suggest closing Gilles' older question as a dup of this one; I think Gilles' older question is better-written and better-researched, whereas I find this question a bit confusing and hard to follow.)
Jun
2
answered Reductionist proofs of decisional problems to computational
Jun
1
awarded  Notable Question
May
31
comment Security of the iterated Hill Cipher
@LinearAlgebra, OK, I've edited my answer to show how to break the revised scheme, given your updated question.