Reputation
23,908
Top tag
Next privilege 25,000 Rep.
Access to site analytics
Badges
6 37 88
Newest
 Nice Answer
Impact
~637k people reached

Oct
16
comment Memory-hard proof-of-work: are they ASIC-resistant?
@CodesInChaos, thanks. Here's my super-crude back-of-the-envelope calculation: a RAM chip costs about \$20; a CPU costs about \$200; so it feels like we're already talking about a potential for a 10x speedup if the cost of the ASIC is as low as \$20 per chip. That sounds like more than a small advantage. Does that sound right?
Oct
16
comment Does an encrypted random sequence conserve its “randomness”?
Minor nitpick: I don't think it's the pigeon-hole principle you mean to quote here.
Oct
12
comment For any hash value, is there an infinite number of inputs that hash to it?
See also crypto.stackexchange.com/q/9910/351.
Oct
5
comment How does RSA compute such enormous numbers?
See also security.stackexchange.com/q/13674/971
Oct
5
comment How does RSA compute such enormous numbers?
What research have you done? This is covered in textbooks and courses on cryptography. We expect you to do a significant amount of research before asking, and to show it in the question. See security.stackexchange.com/help/how-to-ask: "Have you thoroughly searched for an answer before asking your question? Sharing your research helps everyone. Tell us what you found and why it didn’t meet your needs. This demonstrates that you’ve taken the time to try to help yourself, it saves us from reiterating obvious answers, and above all, it helps you get a more specific and relevant answer!"
Sep
20
comment Is ChaCha20 alone sufficient for securing data-at-rest?
You say "ChaCha20 protects your file from being read", but that's an overstatement. ChaCha20 alone doesn't prevent the file from being read: chosen-ciphertext attacks may be able to not only let the attacker flip bits, but also let the attacker learn the plaintext. I realize this is counter-intuitive for many people: it feels like encryption ought to be enough to protect at least confidentiality, but when you have a chosen-ciphertext attack model and an encryption scheme that is only secure against chosen-plaintext attacks, that's the situation you're in.
Sep
15
comment A secure function evaluation problem and an alternative of 1 out of n oblivious transfer?
I think you should explain that these constructions are only secure in the "honest-but-curious" model, which is an odd kind of threat model where we are worried about a malicious adversary but we somehow don't believe the adversary will do anything too malicious. Needless to say this often doesn't match up to what adversaries can actually do in the real world, so we often need something that's secure in "the malicious model".
Sep
11
comment Is there an encryption format that preserves length and only outputs alphanumerics?
I'm not sure that 4 rounds is enough; for a 100-bit block width, you only get a $2^{25}$ level of security, which is uncomfortably low. The scheme would probably be safer with 8 rounds. (There are more modern results than Luby-Rackoff which show better security with more than 4 rounds, as you probably already know.)
Sep
8
comment Theoretical pi-based stream cipher
@CodeJockey, see mathoverflow.net/a/26970/37212 and rec-puzzles.org/index.php/Pi%20Solution.
Sep
3
comment Is there a secure source of entropy on a typical microcontroller?
In practice you should almost never use a strong extractor; simply hashing using a cryptographic hash function will almost always make more sense. (Assuming you are a practitioner/engineering building a product, rather than a theoretician interested in what theorems we can prove.)
Sep
3
comment Could eVoting on the bitcoin blockchain be done?
What research have you done? Have you searched Google Scholar? I feel sure I've seen papers on using the bitcoin blockchain for some aspects of e-voting.
Aug
28
comment Are there ANY text strings that will generate the same SHA-512 Hash output?
Already answered at crypto.stackexchange.com/q/12301/351 and crypto.stackexchange.com/q/8765/351; see also crypto.stackexchange.com/q/301/351 and crypto.stackexchange.com/q/8092/351. In the future please make more of an effort to search for related questions here before posting a new one. Thank you!
Aug
14
comment Is (AES-)GCM parallelizable?
Please ask only one question per question. This site format works best when you ask only one question. If you ask two questions, you can create problems (e.g., if one answer explains the answer to question #1, and another explains the answer to question #2, how are you going to choose which one to accept?). It's usually better to avoid this: if you have two questions, it is often better to post two separate questions -- in 2 separate posts. Thank you.
Jul
28
comment Words having weight near to minimum distance
OK, that's a fine question -- but it's not what your question currently says. So, edit your question to say that. List the requirements you want the code to have, and ask whether such a code exists.
Jul
28
comment Words having weight near to minimum distance
That doesn't help. What do you mean by "we know its construction"? We know the binary matrix $H$; that is a construction of the code. I think my earlier question stands. If you're asking "Does there exist a class of codes for which the problem is easy" then the answer is a trivial but uninteresting yes, and that's probably not what you really intended to ask. If the question is "Please describe all classes of codes for which the problem is easy", then it's too broad for this site. In any case, you need to be more explicit about what the question is.
Jul
28
comment Reduction to cdp,dl or cdh?
You didn't answer my questions.
Jul
28
comment Words having weight near to minimum distance
I'm not sure what you're asking. What do you mean by "the code is known/unknown"? It's part of the input, so it's certainly known to the algorithm. Do you mean, for a specific class of codes, is this problem still NP-hard? Please edit the question to clarify. If so, it'll depend on the class of codes. What class of codes did you have in mind? And what research have you done? Have you done a literature search?
Jul
28
comment Reduction to cdp,dl or cdh?
Where does $x$ come from? Is it random? Is it fixed? (so it's a constant like, say, 7)? Is it part of the input? What do you mean by "distinguishing encodings of $x$"? What are your thoughts? What have you tried?
Jul
27
comment Fast attack on approximate GCD problem?
OK. There are lattice-based algorithms for this problem (Cohn & Heninger), continued fraction based methods, and more. Have you done a literature search? Did you check Google Scholar? I think you'll find some stuff there -- you might want to do a literature search, compile everything you find, then answer your own question with a summary of the known attacks.
Jul
24
comment Terminology: differences between the terms “pre-master secret”, “master secret”, “private key”, and “shared secret”?
Pre-master secret: tools.ietf.org/html/rfc5246#page-58. Computation of master secret, and how it differs from pre-master secret: tools.ietf.org/html/rfc5246#page-64. The session keys are defined and used in the record layer: tools.ietf.org/html/rfc5246#page-16. If you want to know how TLS works, reading the entire spec is a great exercise!