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Preparing To Migrate Off of SHA-1 In OpenPGP
jamie found a note on debian-administration.org, the first in a promised series on migrating off of SHA-1 in OpenPGP. "Last week at eurocrypt, a small group of researchers announced a fairly serious attack against the SHA-1 digest algorithm, which is used in many cryptosystems, including OpenPGP. The general consensus is that we should be 'moving in an orderly fashion toward the theater exits,' deprecating SHA-1 where possible with an eye toward abandoning it soon (one point of reference: US govt. federal agencies have been directed to cease all reliance on SHA-1 by the end of 2010, and this directive was issued before the latest results). ... So what can you do to help facilitate the move away from SHA-1? I'll outline three steps that current gpg users can do today, and then I'll walk through how to do each one..."
'moving in an orderly fashion toward the theater exits'
An elderly application was trampled to death today as everyone struggled to exit the Sha One theater after someone screamed that an unknown assailant had a knife. After the panic, there was no evidence of injuries from the alleged attack and police are still investigating the presence of an actual weapon.
My work here is dung.
Is there any hash function that actually is secure?
Of course the good ol' rot13 !
In reality, given the time and effort, processing power, etc... yeah, there are some secure ones.
They're like locks, they make getting in hard enough that most people will look for an easier target.
He tried to kill me with a forklift!
Perfect security is not feasible. "Secure enough" changes over time.
From TFA, so others don't have to read it, GPG will stay with SHA 224, SHA 256, SHA 384 and SHA 512.
Rethinking email
Is there any hash function that actually is secure?
Of course the good ol' rot13 !
Not secure enough, better apply it twice for double protection.
You can tell the men from the boys by how many times they do things. Like when I restart my computer, I do it three times to make sure it will work when the things start back up inside it.
My work here is dung.
Is there any hash function that actually is secure?
There are some for which no known attacks exist. SHA-256 and SHA-512, Whirlpool and Tiger are all pretty thoroughly-reviewed with no weaknesses uncovered. The NIST hash function competition is causing a great deal of new hash function research and we'll almost certainly get a bunch of great new hash functions out of it -- many of them not only secure, but significantly faster than SHA-1.
If you're thinking that "no known attacks" isn't good enough, keep in mind that's as good as it every gets in cryptography, with the sole exception of the One Time Pad
Note to ACs: I usually delete AC replies without reading them. If you want to talk to me, log in.
by definishion a hash function can't be safe you are taking something that is of unknown size and giving a specific lenght result which will always be the same for a given input.
due to the limited length of the result using inputs larger than the result you can assure at some point there will be a collision (2 diffrent inputs with the same output)
MD5 failed after enough people looked at it and someone figured out how to salt it to get collisions quite quickly.
as proccessing power increases brute force is getting easier - but when you find a way of cutting down the brute force required.. that is when something can become very weak very quickly.
'...if only "Jumping to a Conclusion" was an event in the Olympics.'
I guess I'll just go back to good old MD5.
That is not what secure means with regard to hash functions. Secure means that it is not feasible to construct a document which has the same hash value as a given document (pre-image attack) or to construct two documents which have the same hash value (collision attack). The complexity of these attacks is ideally such that simply enumerating documents is the fastest way (brute force). Reducing the number of documents which you have to try to find a match makes a successful attack more likely. The complexity which is deemed as breaking the hash function depends on the adversaries and time frames relevant to a particular application.
SHA-1 doesn't encrypt things. It makes a hash of them, to verify they haven't been modified.
There are no secrets encrypted with SHA-1 because SHA-1 doesn't encrypt things.
Really stupid question (not a cryptographer), but is there anything wrong with using multiple hash algorithms (hopefully none derived from one another)? Surely breaking two or more hashes simultaneously would be far harder?
E.g., MD5 is broken. But what if we use both MD5 and SHA-1?
Guess the Aussies overpaid, since their $560k "unbreakable" cryptosystem relies on SHA-1. Shock of shocks, I know...
Oh god, that woman is John Romero!
So many major systems are secured with PK systems that depend on SHA-1 hashes now. If this can be broken, someone please put this to good use by making a collision that makes it possible for people to write homebrew code for the PS3 or 360.
I keep hearing about all these hash collisions and how I should be scared, but I wish I could at least get the good with the bad.
http://lkml.org/lkml/2005/8/20/95
One specific thing that would really help would be if debian would make it a priority to do a complete job of packaging the relevant hash functions, along with bindings for popular languages. For instance, I have an open-source perl app that uses digital watermarks. The user can choose between SHA1 and Whirlpool. However, I want to keep my app simple for users to install, and the perl binding for Whirlpool hasn't been packaged for debian yet, so I've made SHA1 the default. A debian user who wants to use Whirlpool with my app has to jump through hoops, e.g., installing the perl module via CPAN. That's actually a real pain for a debian or ubuntu user, because CPAN and apt don't play nicely; you can get in all kinds of screwed-up states if you try to install half your perl modules using apt and half using CPAN.
TFA is talking about gpg. Well, realistically, the choice of hash function is not the bottleneck in terms of security when it comes to sending encrypted or signed email. The bottleneck is mainly just that it's too hard to use (isn't built in to most GUI email clients), and in the case of encryption it also suffers from negative network effects -- there's no big benefit to me from using gpg encryption in my email unless the people I'm communicating also use the technology. The world's best crypto doesn't do you any good if you don't use it because it's too much of a pain. I think gpg is clearly a case where the perfect has been the enemy of the good. They've been so hung up on protecting the user against obscure vulnerabilities that they've ended up making the darn thing too hard for the vast majority of users. The docs, last time I checked, were basically written in Martian. I have a bachelor's degree in math, I program computers as a hobby, and I've read Schneier's Applied Cryptography. I'm not claiming that makes me a big expert on crypto, but it does put me out in front of the vast majority of the population. Well, I simply cannot figure out all the ins and outs of gpg. Okay, I could, but it would take more time than I'm willing to invest.
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If you're thinking that "no known attacks" isn't good enough, keep in mind that's as good as it every gets in cryptography
I think my math teacher would call that a "necessary but not sufficient" condition, I mean anything can be without known attacks by virtue of never having been reviewed. Minimums should include:
1. Published algorithm, no "secret sauce" security by obscurity
2. Solid peer reviews by other cryptographers, definately not just the vendor or their hirelings
3. Strong links to well-researched hard mathematical problems
Of course, nothing can guarantee that the NSA hasn't found some super-secret math thingie that'll cut through it like a knife through hot butter. But cryptography is also about eating your own dog food, if you don't use it for anything valuable who'd trust it? You can't really keep that a secret because you have to tell lots of people that this isn't really secure or they'd use it as if it were. And if you do use it for your valuables, would you really leave that kind of backdoor for someone else to find? Again it doesn't prove anything, but I think most modern crypto algorithms have no weaknesses known to anybody, and if one showed up it'd be just as big a OMG for those who made/approved it as everyone else.
Live today, because you never know what tomorrow brings
According to x509(1) and ca(1), OpenSSL supports md2, md5, sha1, and mdc2 as options for message digests for certificates. Since MD2 and MD5 are already broken, and SHA1 is now suspect, that leaves just the relatively obscure MDC-2.
you must be REALLY stupid
typical ignorant american response.
europeans, particularly the french, tend to use the , for what we use the . for and vice-versa.
so in american, this:
2^57 = 144.115.188.075.855.872
2^52 = 4.503.599.627.370.496
2^52 / 2^57 = 0,03125 = 3,125%
becomes this:
2^57 = 144,115,188,075,855,872
2^52 = 4,503,599,627,370,496
2^52 / 2^57 = 0.03125 = 3.125%
which look like much more reasonable numbers.
...I am moving "off of" this grammar-school newsletter piece.
See also: idioms. No one where I live, ditch digger or professional, would raise an eyebrow at that phrase. Might I suggest you find larger grammatical fish to fry, or perhaps resolve not to get worked up over regional slang?
Dewey, what part of this looks like authorities should be involved?
It's been a while since I had to deal with PGP keys and the like, and things have multiplied since then. Is there a simple explanation for the status/compatability/equivalency of...
pgp
openpgp
gpg
gnupg
And any others I'm missing?
"People who do stupid things with hazardous materials often die." -- Jim Davidson on alt.folklore.urban