20,416 reputation
32473
bio website
location
age
visits member for 3 years, 2 months
seen 2 days ago

1d
awarded  Explainer
Sep
28
comment Question about second preimage resistance of hash function combiner
possible duplicate of Guarding against cryptanalytic breakthroughs: combining multiple hash functions
Sep
28
comment Encrypted database: how to deal with general queries?
@mczraf, in fact, my understanding is that there has already been some industry adoption of CryptDB / the ideas in CryptDB. See e.g. css.csail.mit.edu/cryptdb/#Impact
Sep
28
comment Encrypted database: how to deal with general queries?
Please try to stick to one question per question. I see two questions: (a) how does the industry deal with encrypted databases? (b) is there anything that simulates somewhat homomorphic encryption? Question (a) is too broad. Question (b) is not well-defined (what do you mean by "at least simulate somewhat") so probably not suitable for this site in its current form. What research have you done? Have you looked at CryptDB (which has seen some deployment in industry)?
Sep
28
comment Question about second preimage resistance of hash function combiner
I can't understand the question. What does your notation $H^{s_1}(x)$ mean? Does it mean repeatedly applying $H$, $s_1$ times? If so, what does the notation $H^{s_1,s_2}(x)$ mean? What's $s_1$? I suggest editing the question to clarify.
Sep
23
awarded  Taxonomist
Sep
22
comment Forward pseudorandom permutation
The question is unclear. What vectors? Where did those come from? What does it mean to have the same permutation at the server, in both vectors? I can't follow you. Try editing your question. Specify what is known to each party, what the inputs from each party are, and what the desired output to each party is. Also specify the trust model.
Sep
21
awarded  Popular Question
Sep
17
comment Ciphertext-only cyptanalytic attack agianst the affine cipher?
What research have you done? What are your thoughts? What have you tried? We expect you to do some research and try to solve the problem yourself before asking here. What is the motivation for this question or the context in which you ran into it? In particular, are you aware that in practice it is usually easy to find some amount of known plaintext, e.g., through crib-dragging? Note that crypto.stackexchange.com/q/8375/351 and crypto.stackexchange.com/q/5878/351 and en.wikipedia.org/wiki/Hill_cipher describe known-plaintext attacks.
Sep
17
revised Ciphertext-only cyptanalytic attack agianst the affine cipher?
deleted 4 characters in body; edited tags; edited title
Sep
17
comment Ciphertext-only cyptanalytic attack agianst the affine cipher?
@otus, you're right. I'll edit my comment accordingly.
Sep
17
comment Are there cryptographic hash functions with homomorphic properties?
We already have questions here that provide lots of information on this subject. Simply searching on "homomorphic hash" in the search bar at the upper right turned up the following: crypto.stackexchange.com/q/6497/351, crypto.stackexchange.com/q/8074/351, crypto.stackexchange.com/q/12719/351. In the future, you might want to do a bit of research before asking, to help you ask a more informed question.
Sep
17
comment Is appending the hash of the plaintext to the end of an encrypted message sufficient to ensure integrity?
See crypto.stackexchange.com/q/16428/351 and crypto.stackexchange.com/q/9941/351 and security.stackexchange.com/q/13800/971 and crypto.stackexchange.com/q/11440/351, all of which answer your question.
Sep
17
comment On the privacy of perfect hash functions
Do you have a reference? Perfect hash functions in computer science, as normally studied, have nothing to do with cryptography and don't promise to provide any privacy or any other security properties.
Sep
8
revised “Practical” operations supported by functional encryption?
added 75 characters in body
Sep
4
comment Change Salt when Changing Password?
@SteveJessop, I confess I'm not sure if I understand all the details of your scenario. You are aware that you can't start building the rainbow table until you know the salt, and that salts and password hashes are usually not public, right? Are you assuming multiple separate breaches of the password database, and that the user has changed their password in between? That's a pretty rare scenario to target. See my answer for more details.
Sep
4
revised Change Salt when Changing Password?
added 2306 characters in body
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....