Astro Hacker News - Forging 1024-bit RSA signatures in nearly SNFS time [pdf]

tptacek |next [-]

The most important thing to know about this work, which is awesome, is that it relies on access to a raw RSA oracle, where you have a public key and an API that allows you to directly do RSA operations with the corresponding key. The idea is that you then lose access to the oracle, and thus to the private key, but you've gained enough information from your session with the oracle to make forgeries in the future.

So it's not a straightforward general-purpose RSA-1024 signature break; it's pretty situational. The paper goes into detail (in section 5) about how those situations can emerge in practical scenarios.

deprave |root |parent |next [-]

It’s important to note that by “raw” they mean without padding, which is more rare than just a signing oracle, see section 7 of the paper.

bflesch |root |parent |next |previous [-]

Thank you for this nice explanation. I skimmed the abstract but didn't really understand it.

hn_submit |root |parent |previous [-]

All these articles are merely clickbait. I knew there wasn't a real break in RSA before reading the article. It's just some weird subset of usage which allows this. It's nowhere near breaking RSA.

Why are we even contemplating quantum computers breaking encryption when they can't even factorize a 3-digit prime number? I'm wondering if I'll even see quantum computers breaking RSA in my lifetime.

tptacek |root |parent [-]

I'm pretty sure you just described an IACR paper --- with Nadia Heninger's name on it --- as "clickbait"?

yababa_y |next |previous [-]

in the PDF metadata we find the proper and appropriate title of this work:

    Nearly SNFS-Speed Signature Forgery Sans Factoring N (NSNFSSSFSFN)

RossBencina |next |previous [-]

I was expecting to see mention of Microsoft/Apple executable code-signing in the examples. I know key lengths are well beyond 1024 now, but on the Microsoft side it was (is?) possible for USB tokens to be distributed in the mail. What I don't know is whether the tokens could be used as oracles in this attack.

nk_kolja |next |previous [-]

I was unaware of snfs algorithms for generic moduli and/or signatures. Very nice. The theoretical result is purely due to the 2007 Joux et al. paper. What’s new is the implementation and the 1024-bit rsa signature forgery.

Also no ai, so we can expect some speedups soon.

I really didn’t expect rsa to be targeted so much this year. Hope that these results will motivate people to pursue algorithmic improvements!

benmmurphy |next |previous [-]

nice poem at the end of the paper

keeganryan |next |previous [-]

[dead]

pseudohadamard |next |previous [-]

Another piece of overblown academic panic-mongering. It's been known since forever that you never use RSA that way, which is why every single standard that specifies RSA use also specifies padding mechanisms designed to avoid this, but nowhere in the title or abstract, which is about all that 99% of non-cryptographers will read, does it ever mention this. In fact it's written to imply the exact opposite.

This is not "we broke RSA", it's "we managed to find an implementation you've probably never heard of before that's so broken that an attack that nothing should be vulnerable to is actually feasible". This is a blog post, not a news story. I found a much bigger vuln than this in Android RSA auth some years ago, I'm talking beginner-level crypto misuse, told Google about it, and it was quietly fixed. I didn't publish a paper about it or get it in the news because it was a non-story.

Except that in this case every single piece of crypto code or downstream app out there that has the name "RSA" associated with it, which is all of them, has to reassure every one of its users who have seen the news headline that no, it's overblown hype, you're not vulnerable, nothing to do since there's no vulnerability present in your use of RSA.

The worst possible outcome would be if this thing actually gets a CVE assigned to it. How do you fix a "vulnerability" that doesn't exist?

angry_octet |root |parent |next [-]

It is a rare privilege to read such volcanic straw-manning.

pseudohadamard |root |parent [-]

Actually it's just thoughts from someone who has to deal with the fallout from this stuff. Which will include spending at least a week researching and writing up a sufficiently nontechnical analysis for mgt explaining why its completely irrelevant, all wasted time I should be spending dealing with actual real security issues.

angry_octet |root |parent [-]

But is that the fault of Heninger et al? Far from being academic and alarmist attention seekers, they have done the hard yards of dealing with real hardware, albeit a reduced difficulty variant.

nullc |root |parent |previous [-]

From a security perspective perhaps it's not that interesting-- although signing oracles are all too common access to one is already close enough to a total break even before getting to the padding restriction. (e.g. go ahead and sign post dated certificates too).

But the technique is interesting as an object of study, in a way that finding "beginner-levle crypto misuse" absolutely wouldn't be, so it makes it more relevant as an academic publication. It further clarifies just how fragile these constructs are.

Also from a security perspective I suspect this may be a total break on some blind signature token schemes that use RSA. I've seen some of those avoid using ECC on the basis of the complexity required to avoid one-more-signature attacks that require making a fair number of concurrent blind signatures. (and have a shape a lot like this attack!)

> How do you fix a "vulnerability" that doesn't exist?

Don't make a signing oracle (esp one that doesn't even do the padding itself) available!

upofadown |previous [-]

From the article:

>Still, some real-world systems continue to use blind-signature, also known as textbook, RSA.

I think those are two different things.