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Oct
26
comment How can rainbow tables be used for a dictionary attack?
@ThomasPornin ah, thanks, I've used the wrong formula, looked that bit up quite hastily. Will fix. Also, yes, you could compress it down, but even so, a 400GB table for just 6-digit passwords is huge. And we haven't added in 5 and 4 digit passwords either; it only counts passwords of exactly 6 digits.
Oct
11
comment Encrypt-then-MAC Confidentiality, Integrity and Authenticity
@JohnBlack yes. In general $m$ should be the encrypted output (which may or may not include IVs depending on the protocol etc) and $k$ the MAC key. So then you calculate your MAC from the encrypted data, which prepends the MAC according to HMAC. Then to verify, the recipient can use the same encrypted data and the key - calculate the MAC and compare. If it isn't valid, they discard the message.
Oct
10
comment When is an asymmetric scheme considered broken?
@PaŭloEbermann ah, so it is!
Sep
26
comment How should one implement a delegated shared trust protocol?
I've removed all the comments under this question as I don't think there was anything positive in the discussion taking place. Just a polite reminder to everyone to keep it constructive and on-topic please.
Sep
26
comment Can a computationally unbounded adversary break any public-key encryption scheme?
Good morning everyone. So in the interests of not letting this get out of hand - here's what I think. I think it's hard to criticise constructively and not hurt feelings. That said, @D.W. I think the best course of action when you disagree with something is to use your vote (you're entitled to do that) - for minor issues (did you mean XYZ?) comments work, but otherwise propose an alternative solution. That way the better answer should be voted up more - comments have much less visibility in terms of being read.
Sep
1
comment How can we reason about the cryptographic capabilities of code-breaking agencies like the NSA or GCHQ?
@gokoon there's been a lot of support for this question, so I've re-opened it - during the discussion Paŭlo mentioned improvements were suggested - we've incorporated those. What do you think?
Aug
27
comment How does asymmetric encryption work?
@Jug True. For very simple examples this falls down fairly easily; however, the nth-root under a modulus becomes more difficult. Multiplication as a whole often has situations where division is a much more difficult concept (matrices, for example). Obviously it doesn't make a great cryptosystem, but it is a place to start to look for possible trapdoor functions compared to addition, which is usually quite simple to reverse.
Aug
26
comment If a cryptanalytic breakthrough is made, what process should be followed?
I've edited the question to make it more generic; let me know what you think (I can always roll it back, or the OP can). I think, personally, that it is a difficult case to decide if this question is in-scope, so I'll be guided by everyone else. Also, I've introduced an ethics tag which may or may not be a good idea - anyone with any better suggestions (soft-question?) please shout.
Jul
26
comment UMAC: to what extent is it in use today?
I think that pretty much covers everything I wanted to know... have a green tick!
Jul
14
comment How do I apply differential cryptanalysis to a block cipher?
Thanks for that; I've had a chance to review those links and they're definitely helpful!
Jul
12
comment Necessity of Randomness of Salts?
@Paŭlo Thomas answers this in his comment with the two-password same salt problem. Perhaps I should have a 3) for that? Also, there is a practical consideration - what happens if you change user name for any reason? You'd need to recompute the hash, so you'd need the password to be input. That may or may not be acceptable to you.