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Sep
4
comment Change Salt when Changing Password?
@BobBrown, are you assuming the password database is breached twice, at two different points in time? That is very rare.
Sep
4
comment Change Salt when Changing Password?
@otus, I suggest you clarify the attack model. The normal attack model is: at some point in time, the password database is breached. At that point in time, the attacker learns the salt and the password hash at that single point in time. Normally the salts and password hashes are not public and so the attacker cannot observe their values before or after that point in time. So even if the user changes their password many times, the attacker won't get to see more than one password hash -- the password hash at the time when the database was breached. So this doesn't help the attacker.
Sep
4
comment Change Salt when Changing Password?
@RichieFrame, there is no point in building a rainbow table to target a single account. At that point a rainbow table has no advantage over straightforward exhaustive search. What a rainbow table gets you is the ability to amortize effort across multiple accounts (to some extent). If you don't have multiple accounts, there is no amortization, and no reason to build a rainbow table. Lots of misconceptions about rainbow tables....
Sep
4
comment Change Salt when Changing Password?
@SteveJessop, if the account has a high-quality salt, a rainbow table is useless regardless. (I've noticed there's a lot of misconceptions out there about rainbow tables... They are cool, but they are not magic -- they do have limitations.) It's not correct to say that if you don't change the salt the rainbow table is useful. If your salt is unique there is absolutely no point in using a rainbow table. If the attacker knows the salt, the attacker might as well do exhaustive search; that's strictly better than a rainbow table. If the attacker doesn't know the salt, he has no hope.
Sep
4
comment Change Salt when Changing Password?
If a different salt is used for each account, creating a rainbow table would be stupid: it won't work, and it'll be inferior to straightforward exhaustive search. Basically, rainbow tables already don't work (they don't provide any speed-up over exhaustive search) if you use random salts, even if you don't change them. So the purported advantages listed in this answer are not actually advantages of changing the salt...
Aug
28
comment How does Random Oracle and Standard Model differ?
possible duplicate of What is the “Random Oracle Model” and why is it controversial?
Aug
28
comment How does Random Oracle and Standard Model differ?
What research have you done? There is lots written on this subject, both in textbooks and in Wikipedia, as well as on this site (try clicking on the random-oracle-model tag under your question to see other questions). I expect you to do a significant amount of research before asking, and to show us in your question what research you've done, and to use the research to frame a narrower question. There is little point in us repeating the information that is already widely available on the Internet. It looks like you haven't done that, so your question isn't a good fit for this site.
Aug
27
comment Is hashing a list of hashes safe?
This is helpful, but it doesn't actually list the bottom-line answer: does this increase the risk of collision? I think the bottom-line answer is no, it's safe -- and it might help to add that to your answer.
Aug
27
comment RSA was rejected by which journal?
What research have you done? Where did you hear this? Are you thinking of Merkle's puzzles?
Aug
24
comment Efficiently map $2^n$ unique 64-bit vectors to $2^n$ $n$-bit vectors where $n < 64$?
How are you going to represent the set of $2^n$ unique 64-bit vectors? What does that set look like? The answer is going to depend upon these details. Depending upon what your set of $2^n$ 64-bit vectors looks like, the answer might be very different. Therefore, we can't answer the question until you edit your question to give us that sort of information; I'm voting to close as "too broad". You can fix the question by editing it. (Also, I suggest you edit it to tell us what you tried and what research you've done on your own. You did do significant research before asking, right?)
Aug
24
comment How does compression before encryption leak info about the input?
"I'm pretty sure adding an "evil" chunk to a JPEG image won't leak the "good" part." - I don't know how you could possibly know that. Anyway, I believe my answer answers that question that was asked.
Aug
19
comment Simple proof that shows AES is not a uniform permutation on any n-bit string?
@Gilles, assuming the author means that it is uniformly distributed on the set of all permutations (when the key is randomly chosen)... the other thread proves that AES does not have this property. Of course, Dimitry's answer is an excellent answer, too.
Aug
19
comment Simple proof that shows AES is not a uniform permutation on any n-bit string?
possible duplicate of Block cipher and parity of permutation
Aug
15
comment Are there any cryptographic flaws in my webhook signing process?
@JessieA.Morris, for what it's worth, there are multiple different ways one can do TLS with client certs; they don't all require having a single trusted CA. But I've said my piece.
Aug
15
comment Are there any cryptographic flaws in my webhook signing process?
@JessieA.Morris, you're still creating your own mini-protocol. My advice stands. P.S. I'm not certain you mean by "work". Your statement that client-side certs introduce more work doesn't sound right to me. If you mean development cost, I don't agree. If you mean computation time, then I suggest you benchmark it, but I bet you'll find that TLS client certs are no worse than anything else that involves a client-side signature. Either way, if TLS+client certs doesn't meet your needs, you should clarify the question by being more precise about requirements.
Aug
15
comment Are there any cryptographic flaws in my webhook signing process?
Is there a reason you aren't just using client certificates? They were designed for solving this problem. The TLS folks thought a lot about the security challenges, so you wouldn't have to.
Aug
2
comment run length testing
This question looks off-topic to me. The site is for questions about cryptography (see here); your question does not appear to fit the fall within the scope of the site.
Aug
2
comment Theoretical attack on RSA
What's your question, specifically? This is not the place for open-ended questions ("Please leave opinions on that") -- this is for specific, answerable questions. In any case, this is a duplicate of the other question that Ricky Demer identifies.
Jul
31
comment Questions on FHE over the Integers - the question modified!
@JongHyunKim, please don't use comments to ask a new question. Comments should only be used to help the author of the answer improve their answer. (This is not a discussion forum; see the faq for more details on how to use this site.)
Jul
29
comment Is it secure to use Diffie-Hellman key agreement to generate a nonce?
@YoavR., it sounds like you are using terminology in a non-standard manner. I don't know what you mean by "this is Nonce - by design it uses counter". I don't understand why you think a MAC "doesn't fit"; your explanation didn't make any sense to me. Again, if you want to receive help, edit your question to specify the security goals you are trying to achieve, what your requirements are, what mechanisms you have considered, what ones you have rejected, and why. I have to say this sounds like an instance of an XY problem.