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Comment: Making False Assumptions (Score 1) 409

by 0ptix (#35155076) Attached to: Are You Sure SHA-1+Salt Is Enough For Passwords?

You are making very strong assumptions about your AES256 implementation (or what ever other block cipher).

On a technical note you assume that whoever coded the implementation of AES did not chose to make it so that it only decrypts a ciphertext with a valid password and otherwise returns "fail". This is trivial to implement: to encrypt m as 0000...000|m. To decrypt, first decrypt then check if the result has 0000...000 as a prefix. If not output "fail" otherwise output m. This this could well be considered a "useful" feature of the implementation as it avoids higher level applications using AES from having to deal with bad passwords.

More formally, from a crypto stand point you also make un-realisable assumptions. A block cipher is essentially pseudo-random permutation. You are suggesting that selecting a random PRP p1 from the AES family (i.e. a random password), computing it in the forwards direction to get p1(m)=c, then selecting another (arbitrary!, not random) PRP p2 from the family and then inverting it to get p2^-1(c) = m' would give you a uniformly distributed m' that is independent of m and p1. No way. Formally you are assuming AES is a family of (invertible) random oracles! But it's trivial to see that random oracles can not be implemented by any poly-time algorithm. So regardless of how it is implemented this can not possibly be more then a heuristic.

Conclusion: don't assume decrypting with a bad password gives a random output independent of the message in the ciphertext. This is an extra (and formally a false) assumption on your implementation!

Comment: google did something and is involved. (Score 4, Informative) 323

by 0ptix (#35064738) Attached to: Egypt Goes Dark As Last ISP Pulls Plug

Dude... seriously?

At least they SOMETHING to help the people in egypt. What do you want? a full scale google invasion?

And by the way a google employ (exec) was kidnapped by plain clothed security forces in cairo and is missing since several days. The arrest was caught on video. See around 1:11

Not quite so cushy after all.

Comment: Local solution (Score 1) 323

by 0ptix (#35064688) Attached to: Egypt Goes Dark As Last ISP Pulls Plug

I was talking to a guy from telecomix on irc yesterday who was working on a pretty sweet project trying to get net and phones to people in egypt. Generally they seem to be organizing quite a few cool things. In this case the guy was gearing up to buy a bundle of phone lines (enough for about 2000) and hooking it up to a computer with SIP on the egypt side. The end goal was to setup what is essentially a new Dial-in ISP. But I didn't really have time/knowledge to understand the details. Anyway they're doing some pretty rad stuff so it's worth checking out.

Still, there really is only so much you can do given just a couple days notice and a country in the middest of an information lockdown (not to mention a general revolution).

Comment: Re:Text to speech (Score 1) 323

by 0ptix (#35064612) Attached to: Egypt Goes Dark As Last ISP Pulls Plug

I've been following the situation quite closely now on twitter for several days and a surprising number of tweets coming from inside egypt are actually in english. Search for hashtags #jan25 and #feb1 to see what i mean. Even now with all ISPs down people are still finding ways round the blockade and tweeting. (Of course many of those tweets are not actually from inside egypt especially now. But still over the last few days many were.)

Also from the google blog post announcing the new service: "People can listen to the messages by dialing the same phone numbers or going to twitter.com/speak2tweet." So they do seem to provide a way to get information and not just give. Haven't tested it myself though.

Comment: ALL asymmetric crypto rely on P != NP (Score 1) 700

by 0ptix (#34944574) Attached to: Polynomial Time Code For 3-SAT Released, P==NP

Here's your evidence:

Given a public key for an asymetric cryptosystem (say a modulas n for RSA) it is easy to verify (i.e. in NP) that a candidate secret key (say primes p and q in the RSA case) match the public key. Paraphrasing heavily now: If P == NP then anything that is easy to verify if polytime is also easy to solve in polytime. In our case that means if i give you a public key you can now FIND a matching secret key in polytime. I.e. if i give you n which is an RSA public key you can factor it into primes p and q. But if you can find the secret key for any public key algorithm (including RSA) then no such algorithm can be a "secure" cryptosystem.

Heading off some misunderstanding: We do not know how to base security ONLY on P != NP. In fact that is considered one of the largest open problems in modern theory of crypto. While I just argued that P!=NP is a _necessary_ condition for all asymmetric (and most symmetric) crypto to be secure it is not known to be _sufficient_.

We're getting closer with some of the recent advances in Lattice based crypto but were are definitely not their yet. For the theory people out there: A fundamental problem here is that NP tells us something about worst case hardness but for crypto we need average case hardness (i.e. for a random secret key and random coins for the ciphertext). Bridging this gap is highly non-trivial. Recent work in lattices has shown such connections and how to use it for certain problems. However the choice of parameters we use for the resulting cryptosystems are not known to result in NP-hard underlying problems.

Comment: Re:Not secure (Score 1) 164

by 0ptix (#34345046) Attached to: Hong Kong Team Stores 90GB of Data In 1g of Bacteria

Indeed that would be the case. The data is not actually encrypted as claimed by the group, but rather just encoded. In other words there is no secret password required for recovering the data. Instead all you need is to know the scheme used to encode/decode the data.

By the same token ASCII would be an "encryption" of Roman alphabet (amoungst other symbols). Clearly that's just BS.

Comment: more evidence to the contrary (Score 1) 470

by 0ptix (#33682314) Attached to: China Embargos Rare Earth Exports To Japan

Indeed the post is one of the few big news sites i could find that even mentions the story. And as pointed out in the parent post they quote all kinds of denials.

Reuters and BBC for example do not even mention the embargo one way or another.

Does anyone involved have any evidence one way or another? some one working for a japanese company expecting deliveries for example? It would be nice to get some clarity on this...

Comment: Re:Virtualization doesn't work vs. file macrovirus (Score 2, Interesting) 129

by 0ptix (#31764600) Attached to: Researcher Releases Hardened OS "Qubes"; Xen Hits 4.0

I guess the idea is to run adobe PDF in it's own VM that has minimal permissions. Then when it is infected the virus can't access anything the VM isn't allowd to. (grsec let's you do something like that with the ACLs, roles and users.) For example if you do updates manually then you can restrict the VM of adobe Reader to not have net access. so the virus couldn't contact the outside world either. it's all a question of how much you're willing to compartmentalize your system. the more hassel you are willing to deal with the more secure you can get it (up to a point). This also addresses another comment in this discussion that claims that shoddy coding is not addressed by this fix. the idea of this and similar OSs is to limit the damage after said shoddy coding has been exploited. Not to fix the actual exploitation of that coding.

What i don't get is how this systems is really different from the ACL system of other secure OSs such as grsec... i mean on a high level it seems to be about the same thing. each is a different solution to the same problem of how to compartmentalize your system. in this light what advantage does the new VM based system have over grsec? compartmentalization at a lower level maybe? i.e. even internal to the kernel etc. I don't know enough about how grsec is implemented to know if that is really a difference...

"Kill the Wabbit, Kill the Wabbit, Kill the Wabbit!" -- Looney Tunes, "What's Opera Doc?" (1957, Chuck Jones)

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