Google Has Demonstrated a Successful Practical Attack Against SHA-1 (googleblog.com) 143
Reader Artem Tashkinov writes: Ten years after of SHA-1 was first introduced, Google has announced the first practical technique for generating an SHA-1 collision. It required two years of research between the CWI Institute in Amsterdam and Google. As a proof of the attack, Google has released two PDF files that have identical SHA-1 hashes but different content. The amount of computations required to carry out the attack is staggering: nine quintillion (9,223,372,036,854,775,808) SHA1 computations in total which took 6,500 years of CPU computation to complete the attack first phase and 110 years of GPU computation to complete the second phase.
Google says that people should migrate to newer hashing algorithms like SHA-256 and SHA-3, however it's worth noting that there are currently no ways of finding a collision for both MD5 and SHA-1 hashes simultaneously which means that we still can use old proven hardware accelerated hash functions to be on the safe side.
Google says that people should migrate to newer hashing algorithms like SHA-256 and SHA-3, however it's worth noting that there are currently no ways of finding a collision for both MD5 and SHA-1 hashes simultaneously which means that we still can use old proven hardware accelerated hash functions to be on the safe side.
Re:Practical? (Score:5, Interesting)
It is all about cost-benefit. CPU speeds continue to get faster, and renting CPU time on cloud providers become cheaper and cheaper.
Why is this significant? There are still major certificate authorities out there with intermediate certificates using SHA-1. Find a collision for these certificates, and you essentially become a new intermediate certificate authority with the ability to issue domain certs for basically anything you want and they'll validate in browsers.
Now thing of government agencies or crime syndicates that could afford the CPU/GPU time to do this. It is a highly practical attack vector now.
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Yeah, um...except for a 3 letter agency with a 10 or 11 figure budget or a Google no one has the money to devote this much CPU time to one attack. SHA-1 is still fine unless your worried about 3 letter agencies in which case you probably have bigger problems than just encryption -- problems like drones with missiles attached.
Re:Practical? (Score:5, Insightful)
Well, what exactly a time unit of CPU computation means isn't defined (it's like saying "This item cost me 500 monetary units", there's no context), but if we just take it to mean a literal amount of time on any random CPU...
6,500 years of CPU time potentially costs as little as ~$171k USD at Amazon, and compute costs are continuously falling.
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Well, what exactly a time unit of CPU computation means isn't defined (it's like saying "This item cost me 500 monetary units", there's no context), but if we just take it to mean a literal amount of time on any random CPU...
6,500 years of CPU time potentially costs as little as ~$171k USD at Amazon, and compute costs are continuously falling.
how did you come up with that price?
Spot pricing on a 36CPU c4.8xl is currently $0.46/hour.
6500 years in hours / 36 * $0.46/hour [wolframalpha.com] is $728K
Spot pricing may go lower from time to time, but on-demand pricing for the c4.8xl is $1.80hour, so $0.46 is already a significant discount. The upcoming c5 series should help with pricing.
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If you were actually going to do this, you would NOT use a CPU. A data-lite computation-intensive task like this is ideal for FPGAs, where it could be massively parallelized. If you needed to run multiple MITM attacks [wikipedia.org], then you could fab some ASICs and cut the hash/joule cost much more. There is likely some NSA datacenter in Utah doing this right now.
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If you were actually going to do this, you would NOT use a CPU. A data-lite computation-intensive task like this is ideal for FPGAs, where it could be massively parallelized. If you needed to run multiple MITM attacks [wikipedia.org], then you could fab some ASICs and cut the hash/joule cost much more. There is likely some NSA datacenter in Utah doing this right now.
But Google actually did it and they say they used CPU's.
if you happen to have thousands of CPU's laying around that aren't always busy, using CPU's is apparently feasible.
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Re: Practical? (Score:2)
How? Perhaps the parent poster has government discount price in.. Busted!
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The cheapest EC2 node has one CPU at a reserve pricing as low as $0.003 for a t2.nano instance. The exact math I used is:
(6500 * 365 * 24) * 0.003 = $170,820
I realize that a nano instances don't really have much CPU power available (they're intended to be used for bursty tasks), but Google didn't define what a "CPU hour" was, so neither did I.
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The cheapest EC2 node has one CPU at a reserve pricing as low as $0.003 for a t2.nano instance. The exact math I used is:
(6500 * 365 * 24) * 0.003 = $170,820
I realize that a nano instances don't really have much CPU power available (they're intended to be used for bursty tasks), but Google didn't define what a "CPU hour" was, so neither did I.
Like you said, t2's aren't meant for sustained CPU use. You only get 30 minutes of full CPU use after launch, and they further limit how many t2's you can launch with the full initial CPU credit (100 per day) - so you can't just keep launching new hosts to reset the CPU balance and run out the balance for 30 minutes then relaunch. After you use up the initial credit balance, they throttle the CPU to 5% and each hour they give you another 3 credits (which will let you run at 100% cpu for 3 minutes). They've
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Assuming Amazon has sufficient capacity, it could be completed in an arbitrarily short amount of time by spinning up enough instances. Amazon bills by aggregate time, so the cost of one node for two days is the same as the cost of two nodes for one day.
My point was more to show that it's potentially achievable without Google or NSA sized budgets, and that the cost would only shrink from there over time.
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You can do it cheaper by using botnets rather than legitimate resources.
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CPU time is perfectly well defined [wikipedia.org], though only really meaningful in terms of absolute value if you also give the relevant CPU you're talking about (obviously, 1 hour on a 386 and 1 hour on a modern Xeon are orders of magnitude difference levels of computation). Incidentally, they don't give the CPU used for the attack, as due to the fact they used cloud infrastructure the CPU time was spread over many different kinds of CPUs, but their "average CPU" unit reference is a 2.3Ghz Xeon E5-2650v3 (and for GPUs,
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Yeah, um...except for a 3 letter agency with a 10 or 11 figure budget or a Google no one has the money to devote this much CPU time to one attack. SHA-1 is still fine unless your worried about 3 letter agencies in which case you probably have bigger problems than just encryption -- problems like drones with missiles attached.
I can easily throw 1 million cores at a problem. That's 2.5 days to get an answer. My company would be pissed at me for wasting the resources, and would fire me, but I could do it. There are lots of people like me in the world.
Fun fact: a core-year on EC2 Spot generally costs less than $100. No clue how many cores you could get in parallel, but lots of organizations could throw $500k in IT spending at a problem, they just need to achieve something worth more than that by doing so.
I bet doing the same wit
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Governments might have found another easy way in and all a VPN service cert will do is make a gov tracking easy.
Use a VPN, the users must be interesting, crypto funding and gov computer time was not an issue.
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They have an alternative use of the word practical.
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I know you are trying to be funny, but you are inadvertently correct. Everyone here seems to be assuming they are using the definition which is the opposite of 'impractical', when they are actually using the definition meaning 'not just theoretical'.
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If Google can do that, NSA can surely do that - maybe not right now but quite soon.
Also don't underestimate various botnets - right now they are mostly used for spamming/DDOS'ing/crypto currency mining (which in itself is ... hashing) but they can be used for finding collisions in SHA-1 as well.
Also don't forget that "practical" in this case means that an attack can be carried out using currently existing availble computational resources, vs. something purely theoretical which requires billions of CPUs/
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A 10 million strong botnet would need +/- 3 years per key under ideal circumstances here.
Aren't you off by a few orders of magnitude there? 6,500 years of computation time divided by 10,000,000 bots would be about 5 hours and 42 minutes, not 3 years.
Even your hypothetical 10,000-strong botnet could do it in about 8 months, which might be well worth it if it meant being able to hijack a cert that could be leveraged in interesting ways (e.g. using it to sign your malware as an official update for the company).
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How do you figure?
"This attack required over 9,223,372,036,854,775,808 SHA1 computations. This took the equivalent processing power as 6,500 years of single-CPU computations and 110 years of single-GPU computations."
That works out to about 45mil computations/sec for CPU or 2.65 bil computations/sec for GPU.
To get it done in 30 days would take a 79,000 machine CPU botnet, or a 1,342 machine GPU botnet.
Fudge the numbers a bit as they probably won't be running full-tilt for 30 days straight, and they won't all
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Accelerate SHA-1 hashes to nearly the speed of light and then collide them. Capture all of the bits that come flying out to understand what is inside.
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The fact that we aren't talking about time or energy requirements that are on the order of lifetimes of stars or the mass energy of a star should tell you that it broken.
This is probably the best layman explanation of cryptographic security I have ever seen. If the numbers involved in breaking something crypto related can be expressed in easily understandable terms without doing something like this: https://what-if.xkcd.com/96/ [xkcd.com]
Then the crypto thing you are talking about is broken and shouldn't be used.
Re:Practical? (Score:5, Informative)
One of the consequences of the second law of thermodynamics is that a certain amount of energy is necessary to represent information. To record a single bit by changing the state of a system requires an amount of energy no less than kT, where T is the absolute temperature of the system and k is the Boltzman constant. (Stick with me; the physics lesson is almost over.)
Given that k = 1.38×10^-16 erg/Kelvin, and that the ambient temperature of the universe is 3.2 Kelvin, an ideal computer running at 3.2K would consume 4.4×10^-16 ergs every time it set or cleared a bit. To run a computer any colder than the cosmic background radiation would require extra energy to run a heat pump.
Now, the annual energy output of our sun is about 1.21×10^41 ergs. This is enough to power about 2.7×10^56 single bit changes on our ideal computer; enough state changes to put a 187-bit counter through all its values. If we built a Dyson sphere around the sun and captured all its energy for 32 years, without any loss, we could power a computer to count up to 2^192. Of course, it wouldn't have the energy left over to perform any useful calculations with this counter.
But that's just one star, and a measly one at that. A typical supernova releases something like 10^51 ergs. (About a hundred times as much energy would be released in the form of neutrinos, but let them go for now.) If all of this energy could be channeled into a single orgy of computation, a 219-bit counter could be cycled through all of its states.
These numbers have nothing to do with the technology of the devices; they are the maximums that thermodynamics will allow. And they strongly imply that brute-force attacks against 256-bit keys will be infeasible until computers are built from something other than matter and occupy something other than space.
I want crypto that has a good chance of outlasting the heat death of the universe even with a quantum [wikipedia.org] computer [wikipedia.org]. For symmetric key crypto this means you would need somewhere around a 601 bit keyspace IIRC before you exceed the mass energy of the universe [wikipedia.org].
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I want crypto that has a good chance of outlasting the heat death of the universe
Why, are you Doctor Who and got the key to unraveling space and time or something? And even if someone should bother, do you really care if crypto-archaeologists find your tin foil hat conspiracies or pr0n collection (I was considering saying love letters and gf sex video, but it's /.) many thousand years from now when you and everyone who ever knew you is countless generations dead? I do care about 20 or 50 years from now but unless we make significant progress towards immortality in that time, I hardly ca
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There's one context in which their concern isn't unreasonable: the default assumption is that if any crypto system (key exchange, public key encryption, hashing system, etc.) becomes common then people are going to think about it pretty hard. That's going to lead to a lot of insight in how to do better than brute force. The classic example of this is RSA where RSA-129 was estimated by Rivest that it would take on the order of quadrillions of years to factor even assuming the same improvement rate in comput
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So
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The simple act of counting that high on an ideal classical CPU would probably kill all surface life on Earth.
Nope. The energy requirement while substantial is not insurmountable. I believe that the amount of energy to cycle a 128 bit counter through all states on an ideal classical computer is around 10% of the total annual US energy consumption [wikipedia.org]. This assumes an ideal machine which happens to be many orders of magnitude more efficient than even our best computers so using conventional technology it would be ocean boiling energy consumption.
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Nice explanation. However you are describing a scenario where you have 256- bit key and you have to loop through all possible keys and try to decrypt the ciphertext with it - brute force attack. Yes, in such scenario 256-bits is plenty good enough.
There are other attacks that you do not cover. Such as the key was not selected in random or there is non-brute force attack. Or symmetric cryptography is not sufficient in the given scenario and you need to use public key cryptography where the key has differen
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The bit change is not necessary for computation at all from information theory perspective. Theoretically, no energy needed at all for any computation. Whatever, you can do with active circuit, can be done using passive circuit (e.g. your camera lens can be used for FFT). The energy is only needed for reading information. So no matter, how complex the cryptography is, the theoretical energy required to decrypt is zero.
Yes and no. In my understanding as a physicist, bit flipping per se is free, but you need a minimum of 1/2 kT of energy to destroy information (create entropy). To avoid destroying information during computation, you basically need to store every step you do, so the operation becomes reversible (google "reversible computing" for more). This is not usually practical, so most of computing does suffer from the 1/2 kT limit per bit operation.
The lens example is valid IMHO, as Fourier transform is reversible
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How long is 6500 years CPU time in China's top supercomputer? 6 hours over 10 million cores.
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Sunway TaihuLight [wikipedia.org]
The Sunway TaihuLight uses a total of 40,960 Chinese-designed SW26010 manycore 64-bit RISC processors based on the Sunway architecture.[5] Each processor chip contains 256 processing cores, and an additional four auxiliary cores for system management (also RISC cores, just more fully featured) for a total of 10,649,600 CPU cores across the entire system.[5]
What should happen and what will happen (Score:5, Interesting)
Re:What should happen and what will happen (Score:4, Informative)
The second to last Yahoo security breach was so bad in part because the passwords were hashed with a completely unsalted MD5 https://nakedsecurity.sophos.com/2016/12/15/yahoo-breach-ive-closed-my-account-because-it-uses-md5-to-hash-my-password/ [sophos.com]. The lack of salting would have been by itself a problem even when MD5 was still considered secure.
Actually, even with salting, no standard cryptographic hash function is appropriate for password databases. You can squeak by if you iterate the hash function enough times, but even that is pretty weak, since it means that an attacker with lots of GPUs -- or, even worse, special-purpose hardware -- can perform hashes so much faster than you can that the key stretching you obtain is minimal.
The state of the art in password hashing is algorithms like Argon2 [password-hashing.net], with parameters that are tuned to require significant amounts of not just CPU time, but RAM and threads. Argon2, tuned to require, say, 10ms of time on four cores and 256 MiB of RAM, is going to significantly strengthen passwords. The RAM requirement means a GPU with 4 GiB of RAM can only test 16 passwords in parallel, making GPU-based cracking essentially useless, since what GPUs provide is huge parallelism. Custom ASICs would do better, but would still run into bottlenecks on the speed of the RAM. Making really fast cracking hardware would require either huge amounts of RAM, or large amounts of extremely fast RAM. Either way, big $$$.
Even better, if at all possible you should use a hash that is keyed as well as salted. Doing that requires having some place to store the key that won't be compromised by the same sorts of attacks that compromise your password database. In most cases that's hard to do. Argon2 will accept a key so you can get both sorts of protection, though if you can be really, really certain that no attacker can ever get the key, then you can use a standard cryptographic hash function in a keyed mode, e.g. HMAC-SHA256, though I'd still recommend using a purpose-designed password hash (e.g. Argon2) in case your key is compromised.
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The problem with that is on the other practical end: if you massively increase the resources needed will also increase the server side resources; it won't be as bad as it will be on the cracking end, but server resources are expensive.
It won't be as bad as on the cracking end, that's the whole point. The reason for doing password hashing is to exploit the asymmetric level of effort between hashing and brute force search. To make that work, though, you do need to invest as much as you can afford in the server, to move the bar for the attacker as high as possible -- hopefully out of reach of all but the most serious. If you can't afford very much, fine, but realize that you're also not setting the bar very high.
But this is exactly why go
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But this is exactly why good password hashing algorithms are moving to RAM consumption as the primary barrier. It's pretty trivial for a server with many GiB of RAM to allocate 256 MiB to hashing a password, for a few milliseconds, but it gets very costly, very fast, for the attacker. And if you can't afford 256 MiB, how about 64?
Using memory dependent hashes works better if one is a small server since one will rarely have a lot of people sending in their passwords at the same time, so the RAM space you need isn't that large. If you are a large organization then this doesn't work as well because you then need room to be able to do many such calculations functionally simultaneously.
Nope. The leverage factor in the password hashing case is linear, since the entropy of passwords is constant (on average). The leverage factor for cryptographic keys is exponential. The reason we don't use much longer keys for public key encryption, etc., is because there's no point in doing so, not because we can't afford it. The key sizes we use are already invulnerable to any practical attack in the near future. For data that must be secret for a long time, we do use larger key sizes, as a hedge against the unknown.
I agree that there's a linear v. exponential difference there(although for many of these it is more like linear and subexponential due to algorithms like
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Using memory dependent hashes works better if one is a small server since one will rarely have a lot of people sending in their passwords at the same time, so the RAM space you need isn't that large. If you are a large organization then this doesn't work as well because you then need room to be able to do many such calculations functionally simultaneously.
Meh. If you are a large organization, you can afford more.
Anyway, the point is that you should turn it up as much as you can afford.
I agree that there's a linear v. exponential difference there(although for many of these it is more like linear and subexponential due to algorithms like the number field sieve),
Yes, NFS is subexponential, but not very "sub". And anyway, RSA is old, broken crypto which should be migrated away from.
but the rest of your comment is essentially wrong. We keep keys just long enough that we consider it to be highly unlikely that they are going to be vulnerable, but not much more than that.
I hate to resort to appeal to authority, but the actual analysis required to prove it is way more effort than I have time for this morning. Take a look at keylength.com, it has a host of authoritative references.
In fact, it would be a lot safer if we increased key sizes more than we do, but there are infrastructural problems with that. See e.g. discussion at http://crypto.stackexchange.com/questions/19655/what-is-the-history-of-recommended-rsa-key-sizes [stackexchange.com]
Heh. In my previous reply I actually typed a
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If you are a large organization, you can afford more.
Yes, but the point is the way it scales; If you are tiny you can reasonably assume that the almost no occasions will occur when you need to do multiple hashes in a small amount of time. If you are larger then you end up with a lot of extra RAM that you aren't going to use regularly but will need to use during peak log-in times. I agree that you can probably afford more, but getting corporations to do so is difficult; at the end of the day, everyone cares about their bottom lines.
RSA is old, broken crypto which should be migrated away from.
This suggests that you have
Re: What should happen and what will happen (Score:2)
There's a straightforward reason why lots of web apps continued to use MD5 *long* after it was deprecated: MySQL had a function for md5() almost from the start, but didn't have an inline function for SHA() until 4.0.2... and 4.x didn't become the default version in long-term stable server-oriented distros until 2006 or later. Getting a new release to run on YOUR development computer? Easy. Convincing an enterprise sysadmin to let you have it on a production server before it has become the 'stable' default *
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There's a straightforward reason why lots of web apps continued to use MD5 *long* after it was deprecated: MySQL had a function for md5() almost from the start, but didn't have an inline function for SHA() until 4.0.2...
What sane person does their hashing inside their RDBMS? You hash it in code before you store it.
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The sane person who isn't given several days to investigate and implement their own algorithms (not to mention months of testing if you want to be sure you didn't fuck it up) when there's a 3-character function call sitting there waiting to be used.
Especially if they're not crypto experts and don't even know that doing the hash in the rdbms is bad, never mind why its bad. Which, for better or worse, is a large portion of the programming professionals, especially when you're including outsourcing companies
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Ok, I give up. Why is it bad to hash values inside an RDBMS?
For variable values of "practical" and "relevant" (Score:1)
The thing is that there is not actually a lot you can do with an SHA1 hash collision. Sure, you may be able to impersonate a site by use of a fake certificate. But these are around anyways because of CAs with shoddy security and governments that do not understand the value of security and just coerce CAs in giving them out. So an SHA1 collision is actually a bit of overkill for that and likely the most expensive option by a large margin. So what else is left? I do not see anything.
Sure, if this was somethin
Re:For variable values of "practical" and "relevan (Score:4, Informative)
Not a lot you can do?
Anything that requires signatures is vulnerable to forgery if the signer's certificate specifies SHA1.
An attacker could forge:
1. Software signatures - to slip malware into a software vendor's distribution channels.
2. SSL certificates - to MITM web connections to phish, steal data, or distribute malware.
3. Personal digital signatures - to fabricate documents, including emails, transaction, orders, etc that are normally trusted implicitly due to the signature
4. Subordinate CA certificates - to create trusted certificates which permit all of the above
The problem lies with #4. The real risk is not a one-off duplicate of John Doe's smart card. The real danger is the CAs signed with SHA1 who are still trusted by browsers, applications, and OSes around the world. If an attacker counterfeits one of their certificates, he can issue arbitrary certificates for any web site, any software publishers, or any user.
The only solution is to discontinue the use of SHA1 internally and to revoke trust for all CAs that still use SHA1. Better crypto has existed for a long time---the standard for SHA2 was finalized in 2001, well over a decade ago.
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Indeed. Not a lot you can do even when you ignore the high effort needed and that it is a 2-sided collision. I do not dispute that you should not use SHA1 when you want security, but the actual attacks possible at this time are pretty much irrelevant. Your list just confirms that. It looks impressive (well, sort of), but when you take into account the effort of each attack and the possible gain, they become meaningless, because higher gains at lower effort are around plenty.
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Would it be possible to tamper a famous git repo (e.g. Linux) by writing a malicious commit with the same hash?
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TFS says a total of ~6600 computer years.
Get a botnet of ~80k computers and you have it in around a month. That's hardly "meaningless" when we're talking something as globally damaging as a root CA certificate, especially when its coming at a time that we're seeing botnets hitting millions of nodes.
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Not a lot you can do?
Anything that requires signatures is vulnerable to forgery if the signer's certificate specifies SHA1.
An attacker could forge:
1. Software signatures - to slip malware into a software vendor's distribution channels.
That requires a second pre-image attack, not just a collision attack. (What gweihir called "two-sided" rather than "one-sided"... though that is not standard terminology).
2. SSL certificates - to MITM web connections to phish, steal data, or distribute malware.
Also requires a second pre-image attack.
3. Personal digital signatures - to fabricate documents, including emails, transaction, orders, etc that are normally trusted implicitly due to the signature
This one can be done with a collision attack. You generate two different documents which hash to the same value, but have different contents. The PDF format, unfortunately, make it pretty easy to generate documents which look sensible and have this property. It's not possible with more transparent fo
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This can only be done with a collision attack if the CA is really, really stupid. Proper CAs should include chain-length restrictions in their certificates.
Please correct me if I'm wrong, but it appears that most CAs are really, really stupid. Here's a list of the CAs included in Firefox: https://mozillacaprogram.secur... [force.com] . I split the PEMs into a pile of files, and checked them:
$ for pem in * ; do openssl x509 -text -in $pem | grep pathlen ; done
CA:TRUE, pathlen:4
CA:TRUE, pathlen:1
CA:TRUE, pathlen:1
CA:TRUE, pathlen:7
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So out of 172 root CAs only 14 include any path length restrictions, and even the ones who do still allow some chaining.
O_o
We're doomed.
I don't think the SHApocalypse will be tomorrow. This was an identical-prefix attack instead of a chosen-prefix which constrains the attacker considerably, and the computation required is much higher even to generate simple collisions. However, (again, please correct me if I'm missing something) it does seem plausible that that further weaknesses will be found which provide just enough leverage to forge a signature with one of those 172 CAs, and we may eventually see a rogue sha1WithRSAEncryption CA issued.
I concur, completely.
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You seem to miss the point entirely. This is the expected course of degradation for a hashing algorithm. First it becomes theoretically possible, then it becomes demonstrable at extreme cost (meaning only a few organizations could pull it off). Then it becomes expensive but possible, then your watch can do it. From the amount of time it takes to hit these waypoints you can determine when it will be useless. Because changing the course of large organizations is like trying to turn around an aircraft carrier,
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Actually, that _is_ my point. This is not any big news, it is a small step in an expected progression. But my second point is that the value of certificates (what this mostly applies to) is generally vastly overrated.
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But these are around anyways because of CAs with shoddy security and governments that do not understand the value of security and just coerce CAs in giving them out.
There's a big difference between having a systemic flaw and working on social engineering, and the presence of one doesn't invalidate strengthening against the other.
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That is just my point. There is a big difference between a high-effort attack that is hard to do and a simpler one that has been done mass-scale. The second is a real risk, the first one is pretty irrelevant. Incidentally, the defects of the CA system are systematic, and they cannot be fixed by merely moving to a non-broken hash function.
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No you're missing the point. Social engineering and a trust model is not a systemic failure in the sense that the attack is replicatable with any kind of certainty. A broken hash function however is.
You break a hash function, it's broken.
You trick a guy into giving you a certificate to break the chain of trust, doesn't mean you can do it again when that cert becomes revoked.
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You really have no clue about IT Security Risk Management. A broken trust model most certainly is a systematic failure and it is far, far worse than a defect implementation detail like an insecure hash function.
Are two hashes better than one? (Score:5, Interesting)
Any crypto geeks want to weigh in on the truth of this statement? I've often wondered about this. Wouldn't using two hash algorithms be easier and more effective over the long term than getting the whole world to upgrade to the Latest And Greatest Hash every ~10 years?
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Perhaps I was completely wrong [sans.edu] - skip to the Mysid's comment. My sincere apologies then. But this explanation just doesn't work/compute in my head - even today finding MD5 collisions is extremely computationally expensive, yet the person says SHA1 + MD5 is only slightly more computationally expensive.
Let's put it in layman's terms: let's say your cluster made of a thousand GPUs finds MD5 collisions for given data every second. Now finding an SHA1 collision in Google's case required 9,223,372,036,854,775,8
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Re:Are two hashes better than one? (Score:4, Informative)
I think the idea was that one finds an MD5 collision for document A by adding a block of data B to the end of it creating a new documents C. The SHA hash of document C, SHA(C) will not, in general, match SHA(A).
FInding B such that both MD5(C)==MD5(A) and SHA(C) ==SAH(A) is still unfeasible.
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That's for concatenated hashes. As in, you hash the two hashes to form one number, usually by XOR'ing the numbers together. Which can be shown to increase the solution space considerably.
But that reduced the difficulty of breaking SHA1, since you now just need a collision for the length of a shorter MD5 hash.
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It really doesn't matter for the most important use case, because X.509 does not have a way to use more than one hash in a certificate.
And there's a patent for that (US7793097, US20080270788), so unless the owners decide to be benevolent, there's a roadblock to actually implementing it.
Re: (Score:2)
Re: (Score:2)
Any crypto geeks want to weigh in on the truth of this statement? I've often wondered about this. Wouldn't using two hash algorithms be easier and more effective over the long term than getting the whole world to upgrade to the Latest And Greatest Hash every ~10 years?
MD5 + SHA1 is a "new hash algorithm". Think about what you have to do to shift to a new algorithm... all of the message formats that have to be updated, all of the stored values that have to be recomputed, all of the cross-system compatibility dances you have to do to ensure that you can upgrade both sides (or all sides; there are often more than two) in order to update without having to make some error-prone attempt to cut over simultaneously.
The challenge of changing hash algorithms has nothing to do wi
Re: (Score:2)
The GCHQ has most of the worlds mil grade export crypto decryption computer ready thanks to most brands and firms been happy to help the UK gov. Real time decryption was easy and any efforts to link two layers of junk export grade crypto was detected and useless.
The only aspect that slowed th
Re: (Score:2)
True! As for me I usually run downloaded PDFs though virustotal.com and then all scripting features in my Acrobat Reader are completely disabled.
Speaking of ISO's: most Ubuntu mirrors (and their official servers as well) distribute Ubuntu ISO's via ... HTTP and FTP. That's so "lovely" considering that any ISP can easily replace your HTTP traffic. Yes, they have PGP signatures but 99% of people out there have no idea how to verify them. And those PGP signatures are distributed from the same ... insecure ch
Practical (Score:2)
SHA-1 has only been around for 10 years? (Score:1)
I know this isn't the primary point of the announcement, but does anyone know where the authors get 10 years from, as included in this statement: "Today, 10 years after of SHA-1 was first introduced..."? Best I can tell, SHA-1 was formally defined in 1995 (FIPS PUB 180-1), and I'm pretty certain it was in common widespread use long before 2007. Are they referring to the first time it was introduced into one of their own products or something? or I'm I missing something obvious?
Re: (Score:2)
It's been about 10 years since theoretical attacks against SHA-1 have been presented
What about signed code? (Score:3)
I occasionally use a signed .jar in the company intranet. Reading TFA, I wondered what hash is used to sign that? It seems that jarsigner is not willing to divulge, so I had to write a little piece of code aaand ... yup, it's SHA1!
How common is this? Is loads of software now susceptible to attack by replacing a original code by a malware with the same SHA1?
Re:What about signed code? (Score:4, Informative)
Perhaps you could have just read the documentation?
Supported Algorithms
By default, the jarsigner command signs a JAR file using one of the following algorithms:
Digital Signature Algorithm (DSA) with the SHA1 digest algorithm
RSA algorithm with the SHA256 digest algorithm
Elliptic Curve (EC) cryptography algorithm with the SHA256 with Elliptic Curve Digital Signature Algorithm (ECDSA).
If the signer's public and private keys are DSA keys, then jarsigner signs the JAR file with the SHA1withDSA algorithm. If the signer's keys are RSA keys, then jarsigner attempts to sign the JAR file with the SHA256withRSA algorithm. If the signer's keys are EC keys, then jarsigner signs the JAR file with the SHA256withECDSA algorithm.
These default signature algorithms can be overridden using the -sigalg option
http://docs.oracle.com/javase/7/docs/technotes/tools/windows/jarsigner.html
Crafted data (Score:5, Informative)
Re: (Score:2)
What they did is called a chosen plaintext attack [wikipedia.org], and is still damning.
Cached copy of the counter-cryptanalysis paper (Score:1)
The Internet Archive to the rescue:
http://web.archive.org/web/*/https://marc-stevens.nl/research/papers/C13-S.pdf
The paper describes the tech behind the code (linked below) capable of *detecting* the probability of a file + sha-1 hash being either the result of a forgery, or "easier to forge" (from what I understand of the attack against SHA1 done by Google, et all.):
https://github.com/cr-marcstevens/sha1collisiondetection
Now, to try that code against some files as well as the two PDFs google released... :-
At least they don't use it (Score:2)
The web site where it is published use SHA-256
Economic cost was? (Score:1)
Fancy numbers, but they're incomplete. What was the total cost for this 2 year exercise if a ordinary human with a soul sat down and paid for every watt - how much did this PDF experiment cost? The maths has been clear about this for a very long time, google is drinking cool-aid if they think this means anything more than what has already been discussed or discovered.
Let me put it another way, in recent history the A+B=C mathematical formula was proven by a reclusive Japanese mathematician. Have we stopped
Random data storage required. (Score:2)
You may notice they never do these stunts on ASCII text files.
The attack always requires to be able to store a large number of random data on the document.
There are 62 different bytes in the provided PDFs : part of these are the edited message, part of them are the 'attack'. That's 496 bits.
So it may be applied to any kind of document allowing to store about 496 bits of (invisible) data on it (and to be on the safe side, I'm assuming even half of that could be enough).
Not all successful attacks will requir
TLS 1.1 (Score:2)