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May
18
comment Is what i'm trying to do safe?
@VincentAdvocaat, what I meant was that you didn't mention you had tried specifically TLS with pre-shared keys....
May
17
comment Is what i'm trying to do safe?
@VincentAdvocaat, then you should mention that in the question. We expect you to tell us what you've considered and what you've tried in the question. No one likes taking the time to write an answer and then have the original poster come back and say "I already knew of that".
May
15
comment Is what i'm trying to do safe?
@SOJPM, pre-shared keys for TLS seem like a counterexample to the claim that TLS handshakes always require asymmetric crypto -- no?
May
6
comment Brute-force attack given small search-space and hash prefix
This answer is incorrect. It assumes we only have 8 bits of the hash, but as the OP has clarified, we actually have 32 bits of the hash.
May
6
comment Brute-force attack given small search-space and hash prefix
I encourage you to edit the question to incorporate this information. Comments exist to help you improve the question; clarifications shouldn't be left in the comments, as they can disappear at any time, and readers shouldn't need to read the comments to understand what you're asking.
May
6
comment Brute-force attack given small search-space and hash prefix
What's a character, in terms of bits, in your implementation? Is the output of sha1_hex() in hex, so each character is 4 bits of the hash, and the first 8 characters are the first 32 bits of the SHA1 hash?
Apr
27
comment Can cycle finding techniques reduce the memory usage of the MitM attack against 2DES and 3DES?
Yes, it works. It's a standard trick; kudos for re-discovering it. I see no reason the table size would amount to $2^{n/2}$. The complications in working out exact parameters arise when you work out the details of (a) parallelism, (b) distinguished points, (c) the cost of memory and routing networks, to get the exact optimal tradeoff (if you care about constant factors).
Apr
26
comment Adding two public keys
@RickyDemer, I don't know. I guess that's a different question. If you're suggesting that might be what the OP wanted, if so, he needs to specify his requirements or goals in the question. Right now the question only asks for "another, more widely used" scheme. I can only answer the question that was asked....
Apr
26
comment Is there are code hidden in Wired Magazine's December 2014 Issue?
@jww, are you sure you've got the right site? This question is clearly off-topic for PP&CG: codegolf.stackexchange.com/help/on-topic
Apr
5
comment Will ANY prior knowledge assist in determining contents of a SHA1 hash?
@InfernusDoleo, you'll be fine, if that 26-character secret key is truly secret and chosen uniformly using a crypto-quality randomness source. That large secret key means that the space of candidate inputs is very large, so brute-force won't work. The fact that you can see many outputs with related inputs doesn't help given that the secret key is so large.
Apr
4
comment Will ANY prior knowledge assist in determining contents of a SHA1 hash?
@InfernusDoleo, I can't answer that, because it's not clear what you intend the full input to the hash to be. If you want a more detailed answer, list all the parts of the input to the hash and what is known about each. An incrementing nonce counts as a known/predictable part of the input, since it can be predicted.
Apr
4
comment Will ANY prior knowledge assist in determining contents of a SHA1 hash?
You mean knowing some of the input to SHA1, or knowing some of the output? (you talk about knowing parts of the hash, but usually when we say "the hash" we mean the output of SHA1, not the input)
Apr
1
comment How can mega store my login details and still be secure?
@tagyro, thank you for the pointer. Unfortunately, a source code repository is not a substitute for a design document that describes how the architecture addresses these threats. (That said, from xemacs' answer, it sounds like they did exactly what I speculated in my answer.) I think the links to vulnerabilities in early versions of the system are relevant to understanding the history of the system. If there are public documents that respond to that analysis and explain why they're wrong or how they've been fixed, with technical details, I'd gladly update my answer with that information.
Mar
16
comment How to check if a sequence is generated by a linear congruential generator?
What do you mean by "a sequence of numbers starting at the nth bit"?
Mar
11
comment Encrypt-then-MAC: Do I need to authenticate the IV?
This answer contains incorrect statement. 1. It's not just "safer" to MAC the IV; it's unsafe if you don't MAC the IV. 2. "although Mallory can't predict the result of the decryption in any way" - This is simply false. Moreover, I don't know what you mean by "an invalid message", but there's no guarantee that the decryption will be "invalid"; it might be a completely valid message that just happens to be something other than what the sender wanted to send (which would amount to a break of integrity).
Mar
11
comment Is the 1st Encrypted Block Less Secure Than Subsequent Ones?
We expect you to do a significant amount of self-study and research before asking, including consulting standard resources (like Wikipedia and/or standard textbooks). This helps you craft a better question, and sometimes enables you to answer your question on your own. In this case, see e.g. en.wikipedia.org/wiki/Block_cipher_mode_of_operation#CBC. Look at the diagrams there. Why do you think the first block has fewer "permutations" or a closer relationship to the original message? The diagram looks identical for the first block....
Feb
28
comment What would a backdoor in symmetric key cipher look like?
This is already covered by crypto.stackexchange.com/q/1935/351 and crypto.stackexchange.com/q/675/351 (both of which you could have found by searching in the backdoors tag).
Feb
21
comment Anonymous Gravatar Problem
Thank you for the comments. That helps me understand this much better. I encourage you to edit the question to include this extra information -- comments are transitory and can disappear.
Feb
20
comment Anonymous Gravatar Problem
This answer might benefit from a bit more explanation. Where do the ephemeral keypairs come from? (how are they generated, and who knows them?), how do they come to be known to both Gravatar and the site?, and how does this differ from CodesInChaos's previous answer?
Feb
8
comment How many bits can be safely extracted from the BBS generator at each step?
@Nova, but I did answer the question of the OP. (Perhaps you missed it?) The answer is: zero bits, for practical parameters. There is no number of bits that can be extracted safely, with provable security, for practical parameter settings. That does answer the question that was asked.