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Jan
3
comment Why are there no MACs inspired by block cipher modes other than CBC and CFB?
Please clarify your question, especially the statement quoted by Ricky. None of the traditional cipher modes (ECB, CBC, CFB, OFB and CTR) include a MAC, nor can they be (directly) used as one. There are MAC constructions that do bear some resemblance to these modes, such as CBC-MAC and its modern replacement CMAC, but those are separate constructions (although CBC and CBC-MAC do work very similarly). (Also, MAC usually stands for message authentication code; if you really mean mutual, please clarify that too.)
Dec
30
comment Attribute-based broadcast encryption with respect to ABE
Thanks, @Gilles! (Ps. I have no idea why I typed "Ability" instead of "Attribute" above. Must've been a brain fart.)
Dec
30
comment Is the DES F-function injective for a given subkey?
We just had a very similar (but apparently not duplicate) question less than 24 hours earlier. Just out of idle curiosity, are these coming from some online course or something, or is it just a remarkable coincidence?
Dec
30
comment Attribute-based broadcast encryption with respect to ABE
Also, I think we could use a broadcast-encryption tag. Would anyone more familiar with the topic than me want to create one (and look for some old posts to tag it with)?
Dec
30
comment Attribute-based broadcast encryption with respect to ABE
Based on a quick Google search, I assume those acronyms stand for Ability Based (Broadcast) Encryption?
Dec
29
comment Do I have to transfer the private key to digitally sign a remote document?
Also, one specific issue that puzzled me: if the user uploads the document to your server, is there some reason why they can't simply sign it before they upload it? Your server could then verify that the document has been properly signed, using the user's public key.
Dec
29
comment Do I have to transfer the private key to digitally sign a remote document?
Hi, rtan, and welcome to Crypto Stack Exchange. I tried to edit your question to make it a bit clearer, but I'm not 100% sure I interpreted all of it correctly. Could you please check that I didn't introduce any mistakes, and if you find some, edit the question to fix them? Thanks!
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.