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Dec
29
comment Embedded devices Authentication, Integrity and Confidentiality
@DmitryKhovratovich: A per device AES-GCM key can take place of public/private key pairs but what happens if the server was hacked and all the keys go with it? But your point about needing a RNG is quite important, which I really didn't take into account. [Note: This was posted by the OP as a non-answer, because they've apparently lost access to their original account.]
Dec
29
comment Embedded devices Authentication, Integrity and Confidentiality
@RobertNACIRI: When the devices are programmed with public/private key pairs. The public keys are recorded and sent to the server by the admin. The devices are programmed in batches. The server certificate will be CA issued(for revocation and easy verification etc). The client key pair is generated at the factory. A bit like generating GPG key pairs. [Note: This was posted by the OP as a non-answer, because they've apparently lost access to their original account.]
Dec
28
comment How are random numbers for RSA generated?
Related: crypto.stackexchange.com/questions/71/…, crypto.stackexchange.com/questions/1970/…, crypto.stackexchange.com/questions/690/…, crypto.stackexchange.com/questions/2532/…. In fact, I'd say the first two are essentially dupes.
Dec
28
comment How are random numbers for RSA generated?
Ensuring that the number is odd will not save much time testing it, but it will save you some RNG calls. It's not a huge optimization, but it's trivial to make and does provide some benefit.
Dec
28
comment Power analysis and exponentiation by squaring
Thank you for contributing this answer! I do think your answer would be much improved if you could briefly summarize the key points from the references you cite in it. As it stands, your answer does not really provide a stand-alone answer to the question asked. You should also edit the additional information you've posted in the comments directly into your answer, if you think it's potentially worth retaining.
Dec
28
comment Why shouldn't I use ECB encryption?
@FedericoPoloni: Generally, because direct low-level access to the block cipher is sometimes useful for building higher-level constructions, such as new cipher modes. See this recent question for one example.
Dec
28
comment Why shouldn't I use ECB encryption?
@giorgim: Even if you don't have any MAC or AE mode available, using CBC is still strictly better than ECB. If you do have a MAC function, CBC-then-MAC is a perfectly good AE mode.
Dec
28
comment Why shouldn't I use ECB encryption?
@giorgim: There's really no good reason to use ECB (except as a building block for other modes). Pretty much any crypto library provides at least CBC or CTR mode, and if not, they're trivial to implement yourself. Slap an HMAC (or CMAC) on top of that, and you're good to go.
Dec
28
comment What are the security implications of multiple hashing?
Ps. See also this related answer of mine. (I tried to look for it earlier, but couldn't find it here, because it turns out I actually posted it on SO.)
Dec
28
comment What are the security implications of multiple hashing?
@BobBrown: Right. Multiple hashing isn't (necessarily) bad. There are plenty of good and standard algorithms, like PBKDF2, that basically work by hashing the password multiple times. What's generally a bad idea is designing your own non-standard password hashing scheme, without any idea of what makes such as scheme secure.
Dec
23
comment Why shouldn't I use ECB encryption?
@D.W.: I think this is an excellent question for this site, because it asks a simple, common question in a way that invites good answers, makes a great resource to reference later, and is likely to show up well in searches. We've already got several questions that kind of skirt this topic, but this is the first one that just comes straight out and asks the literal question in the title. Not every question here has to be hard in order to be good.
Dec
22
comment Why shouldn't I use ECB encryption?
@supercat: That's basically disk encryption, so you could use modes designed for that. I believe XTS is considered a good choice, although, like all disk encryption modes, it has its limitations (which you should understand before using it). If possible, it should be combined with a MAC of some sort to defend against active attacks.
Dec
22
comment Why shouldn't I use ECB encryption?
Related: crypto.stackexchange.com/questions/225/…, crypto.stackexchange.com/questions/5405/…, crypto.stackexchange.com/questions/12529/…, crypto.stackexchange.com/questions/2963/…, crypto.stackexchange.com/questions/14487/…, etc.
Dec
19
comment What is the fixed point attribute of DES (when used with weak-keys)
@mikeazo: The DES weak keys have been discussed in this question, but I think what Bush is asking about the existence of fixed points for those weak keys, as discussed e.g. here and here.
Nov
17
comment Consequences of AES without any one of its operations
@poncho: That looks like an answer to me. Want to make it one?
Nov
16
comment CCA security of a system that splits messages and encrypts each packet
Is this homework? It appears to be phrased as such. If so, let me just give a hint: en.wikipedia.org/wiki/Malleability_%28cryptography%29
Nov
16
comment Why sorting is needed for Meet-in-the-middle attack
Small note: In practice, you probably wouldn't use a binary search, but rather you'd sort both sets and run a list merge on them. In any case, though, you still end up doing about $O(n \log n)$ comparisons; without sorting, that would be $O(n^2)$, which is no more efficient than brute force.
Nov
12
comment IPsec authentication and encryption lgorithms
As the Wikipedia page notes, actual IPsec implementations typically seem to be on the kernel level (for example, the Linux kernel includes one since v2.5), and so won't generally be portable per se. The underlying crypto algorithms, however, are, and can be found e.g. in the OpenSSL library, which should meet your specs (cross-platform support, written in C). Of course, OpenSSL is really a TLS/SSL library, so it contains a lot of other stuff besides the crypto primitives, too, but as long as you don't mind the extra cruft (which is all in a shared library, anyway), it might be a good choice.
Oct
10
comment Why is TLS SRP verifier based on user name?
@nefarel: Dunno. I might mutter something about Merkle-Damgård length extension attacks, or about provable reducibility to the PRF-ness of the SHA1 compression function, but honestly I have no real idea. It looks sort of like a clumsy imitation of HMAC, but since the folks who designed SRP are pretty smart cryptographers, presumably it's a clever imitation of HMAC, I just don't know exactly how or why. That might make an interesting question in itself.
Sep
25
comment Why are we advising PKI if we know that quantum computers will break them?
Practical quantum computing, like practical fusion power, has been "10-20 years in the future" for several decades already. Basically, in both cases, we thought we knew the theory, and that the rest would be just a simple matter of engineering. Alas, sometimes "mere engineering" turns out to be not so easy, after all.