[H3g3m0n]

Except if /dev/urandom is using a hardware based random number generator, then you have to trust that the hardware hasn't received some NSA alterations at some point during the design.

The NSA did design a random number generator that likely had a backdoor in it: https://en.wikipedia.org/wiki/Dual_EC_DRBG#Controversy).

Here's Bruce Schneier talking about it: https://www.schneier.com/blog/archives/2007/12/dual_ec_drbg_...

Also it's in Windows (although it's not used by default but userspace programs could rely on it). https://www.schneier.com/blog/archives/2007/12/dual_ec_drbg_...

It would be possible for the NSA to go to Intel and get them to put in something in their random number generator that would let them to basically break the encryption by massively reducing the keyspace if they have the secret key.

[patio11]

If you don't trust the hardware, then you've already lost, no matter what algorithmic construction you are using. How are you going to trust your random number generator if 1 + 1 = 2 except when it equals NSA?

(This is one of those times where I regret HN that has twin interests in software security as an engineering science and software security as a political statement.)

[H3g3m0n]

> If you don't trust the hardware, then you've already lost, no matter what algorithmic construction you are using. How are you going to trust your random number generator if 1 + 1 = 2 except when it equals NSA?

You can verify the random number generator. If you know the algorithm and the seed values you can run it on multiple different platforms, or with a pen and paper and verify that the output is as expected and repeatable. If you have large amounts of entropy you are feeding into it, you can log it for testing purposes.

There are also apparently some EC based algorithms that can be used to fix or at lease reduce the impact of a compromised random number generator.

That might not protect against a active attack on your specific system by the NSA (they could send/embedded a magic packet that gives them total control over the CPU for example), might even be possible for it to happen on the NIC controller rather than the CPU if it has access to the system bus. At the least they could flip it into some kind of backdoor random number mode by embedding some extra data in a TLS handshake or whatever. But it should protect against widespread passive surveillance.

[tptacek]

Reducing the impact of a CSPRNG state compromise is a basic design goal for CSPRNGs, and you don't need ECC to do it; the "NSA backdoored" RNG you're referring to is one that no system anyone knows about actually uses, for that reason.

Again: you're making a point that has nothing to do with my comment. If you don't trust RDRAND, don't use it. But you should still be using the OS's CSPRNG. Just make sure your OS isn't using RDRAND. Done and done.

[ig1]

It's about verifiability, you can verify if a CPU is adding incorrectly, there's no way of verifying if the random source is generating randomness correctly.

Integers form a closed group (in the group theory sense) under multiplication and addition, so if you were concerned about specific calculations being compromised you could verify the answer via alternative calculations and testing for consistency.

Faking consistency is likely impossible without causing a huge amount other calculations (which the CPU will do as part of day-to-day operations) to fail. Making the CPU alter calculations only under very specific circumstances and in an undetectable way would require a huge amount of complexity.

On the other hand we know several fairly trivial ways of faking reversable randomness using standard crypto algos that would be statistically undetectable without taking the hardware apart.

[patio11]

Tell you what: You write executable code which tests whether, e.g., Ruby's Fixnum addition is actually adding or not, without using introspection on the implementation. (i.e. You're allowed to test any combination of inputs and outputs, but cannot look within the black box.) Feel free to use number theory, statistics, or a web service which wraps Cthulu in JSON.

I will provide a script which monkeypatches Fixnum such that your test script still reports "Yep, it's still adding correctly" and which will predictably cause 1 + 1 to equal the string "LOL I AM THE NSA" under attacker-chosen conditions.

There are many, many ways I could do this as the crafty adversary, but I anticipate my implementation would be roughly seven lines long and trivially implementable in hardware. (At complexity somewhere between a half-adder and the circuits which we had to hand-draw for our finals in hardware design, which -- obviously -- are a drop in the ocean of complexity on a modern CPU.)

[ig1]

Say you wanted your backdoor to kick-in when I was calculating the fibonacci sequence, will you also detect when I was calculating it via the golden ratio, or via continued fractions, etc. If I can write a test that can show that there's a backdoor because it's not behaving consistently then your attack is significantly weaker then a RNG attack.

You can't just break one calculation under specific circumstances, you have to break any way of verifying it which means compromising pretty much every calculation.

(not to mention you'd have to figure out that it's the fibonacci sequence being calculated and not some other calculation that happens to start with 1+1)

Remember you don't have an interactive attack, you have one chance to build something and ship it out in hardware, and it then has to compromise software that's going to be written in the future.

The beauty of the RNG attack is that it's undetectable, introduces a backdoor into a huge number of systems and it only makes the system vulnerable to the attacker and not to anyone else.

[patio11]

Super double-secret squirrel sources have said there exists a file "nsa_does_fixnum.rb" which is 1006 bytes long and the SHA512 hash of 896e12642f5720d830572a8b11e4c729da3a20c57402758d22a25c46c3c2e6 bb4b09de9030ad591ecb51b8a9a4d4c119cefbf4d51a72db219d94150fb63a 3623. (Concat them -- I broke it into a few lines to avoid breaking the comment page on low-resolution devices.) Our intrepid squirrel didn't get a good look at what it is doing but claims "It doesn't use any external library and doesn't do anything even remotely tricky." They claim that it secretly modifies any Ruby1.8 interpreter to cause 1 + 1 to equal "LOL THIS IS THE NSA" under some circumstances.

Quick ig1, you are freedom's last, best hope. Write actual computer code which can, by adding numbers together and inspecting their output, determine whether your Ruby interpreter has been compromised by the NSA. You're lucky, since the NSA has already shipped their exploit (or did they?), they can't modify it in response to your detection code. Bad news, though: if your detection code fails and an interpreter which includes the backdoor can, after passing your detection code, still get the wrong answer for 1 + 1, an innocent user fails to find the backdoor and suffers a FatalHitByCruiseMissileError. You don't get to say "OK, so in hindsight, now that I see the backdoor addressing it was pretty darn easy. Mop up the mess and I'm sure to win round two."

[acqq]

Sorry, I don't see what you're trying to argument here, since CPUs aren't Ruby interpreters with libraries. CPUs have much stronger limitations under which they have to operate. Remember the Pentium DIV bug? It was discovered.

I'm writing assembly code, I've spent time also to measure the time of the machine operations etc, so I simply can't imagine the valid argument which ignores exact limitations present in actual hardware.

[jsnell]

Can you please break that hash on multiple lines or quote it? It breaks the layout of the comment page.

[ig1]

Your attack relies upon security by obfuscation, hoping that no-one will notice that the behaviour is incorrect (we obviously disagree about the chance that such an attack will be spotted but I think to some degrees that's irrelevant).

The RNG attack has correct behaviour under every statistical and blackbox analysis. The only way you can break it externally is if you have the key.

If you were designing a cryptosystem you'd pick the one where the security lies in the key and not in obfuscation. The same applies when designing an attack you want to keep secret.

[cpeterso]

Linux's /dev/urandom does not trust hardware RNGs any more than other entropy sources. All entropy sources are stirred into the same entropy pool.

[ballard]

Does it use multiple pools a-la Fortuna?

[__alexs]

There's an input pool and 2 output pools but it's not like Fortuna. This is the most up to date analysis of the Linux entropy system I'm aware of http://eprint.iacr.org/2012/251.pdf

[DanBC]

> Except if /dev/urandom is using a hardware based random number generator, then you have to trust that the hardware hasn't received some NSA alterations at some point during the design.

That is a valid concern that needs to be part of your risk assessment. "Do I want to protect my secrets from a well funded government agency?"[1]

But there are other risks that need to be thought about too. Some people seem to think that hardware RNGs are better than software. Often they're not, they're lousy.

HWrngs can have subtle failure rates which are hard to detect.

Once you've done all the de-skewing and other checks they can be quite low bandwidth.

I have a bunch of links to reading about HWRNGs here - (https://news.ycombinator.com/item?id=6060636)

And here's a really nice thread (https://news.ycombinator.com/item?id=1453299)

[1] Although if you want to defend yourself against a well funded secret government agency you need to worry about more than a weak RNG.

[gizmo686]

No you don't. The only time you need to worry about the NSA having a back door into your random number generator is if you are worried either about the NSA attacking you (in which case you probably don't have a chance anyway), or are worried that some learned of the NSA's back door and is exploiting that.

[derefr]

That reminds me of a question I've been pondering on-and-off for a while: is it possible even in theory to use Sufficiently Advanced Mathematics (e.g. homomorphic encryption) to build a trusted computation environment on top of an untrustworthy foundation?

For example, I want to run a VM on EC2, knowing the NSA's after something I have. Is there some way I could, even theoretically, build my VM, that would protect it from the NSA compelling Amazon's cooperation in ripping the data right from my VM's memory at the hypervisor level?

[tptacek]

Possibly. For instance, look up some papers on White Box Cryptography; these are implementations of things like AES designed to run AES computations on untrusted platforms without revealing their key (the key gets "baked in" to the code that runs the algorithm in such a way that it's theorized to be cryptographically hard to extract the key from the algorithm).

You are getting into the flip side of the DRM coin here; put differently: if there's a way to do what you want, there's also a way for the MPAA to do what it wants on PCs.

Personally, I think there is, at least in the dollar-cost model of security.

[bch]

I'm out of my depth here, but since this conversation seems precise, and is discussing theoretical and practical implementations, does this paper[1] factor in? If so, is it fair to say that at some level, without auditing every aspect of hardware, and every aspect of all software used at build time and runtime, you can't know?

[1] http://cm.bell-labs.com/who/ken/trust.html

[ballard]

It's a good insight. There is distinction between I/O (rendering the video and audio to the host) and computations of a seemingly blackbox. Would also be an interesting avenue for malware to grow into if possible. The problem is there's always been decryption code that has to live somewhere that effectively unlocks the whole thing. Edit: PyPy but zk computing for malware.

[homeomorphic]

Wouldn't this make nice foundations for hardware cryptographic tokens such as CryptoStick?

[sweis]

We're working on a similar problem at PrivateCore: Protecting VM data in-use on outsourced infrastructure.

We're running a high-assurance, remotely attestable hypervisor inside the CPU cache and encrypting all access to main memory. This protects against threats from the physical layer, like cold boot, DMA attacks, NVDIMMs, bus analyzers, etc.

It's not quite what you're talking about in your Amazon and NSA scenario. Amazon doesn't let you bring your own hypervisor to run on bare metal and the NSA can compromise the CPU itself.

However, our approach does give you assurance that someone with physical access can't easily snapshot your VM memory.

[derefr]

> remotely attestable hypervisor

How does this bit work, by the way? What's stopping an altered hypervisor from lying to say it's unaltered? (This is the classic "how do you verify a player on your FPS isn't running a bot instead of a game-client" problem in a nutshell.)

[sweis]

Today we rely on the TPM to measure the state of the system using Intel TXT. These measurements are stored in platform configuration registers (PCRs) on the TPM device.

There are known TPM and LPC bus vulnerabilities. That is why long-term we will move away from that dependency by utilizing upcoming CPU features.

[e12e]

> our approach does give you assurance that someone with physical access can't easily snapshot your VM memory.

But how do you know the VM (or rather the hypervisor for the vm) is running on physical hardware, and not in a hypervisor?

I can't think of a way you could be certain of this remotely? Perhaps you could be on-site for the boot-up, and then rely on the fact that snapshotting is very hard -- but it sounds rather fragile...

Still very interesting project! I've been thinking a bit on "running inside the L/1/2/3 chache"-lately - but I hadn't thought about the particular idea that you could treat RAM as "external" -- assuming you could guarantee that you're always in cache.

[sweis]

You must first remotely attest the hypervisor using TXT before deploying a VM to run on it.

Today, that attestation process relies on a TPM and a signed certificate chain baked in by the TPM manufacturer. This is standard stuff out of the Trusted Computing Group.

One more thing to add, this isn't just a personal side project. We're a company and have a beta product deployed to early adopters.

[e12e]

I realized that you probably did have a product -- unfortunately that doesn't mean that the product works (not trying to imply anything about your product/company here; it's just (as you probably know) there many companies selling security solutions; and very few that seem to be selling security solutions that work...).

Are you aware of:

  "Overcoming TPM by exploiting EFI overflow"
  http://www.youtube.com/watch?v=4bM3Gut1hIk&feature=player_detailpage&t=1655

and:

  "Coreboot/bios malware":
  http://www.youtube.com/watch?v=umBruM-wFUw&feature=player_detailpage&t=2297
  

It's an interesting use of TPM -- and sounds like a sound approach, assuming there aren't any bugs in the TPM software... which might be too big an assumption.

I don't suppose any of your software is available as open source? Where can I/we learn more?

[ballard]

Funny you should mention this. I was asked to "suggest solutions" to this in 2008 as a client-facing AWS enterprise consultant in the mobile industry.

The naïve way relies on: "If there isn't a Rootkit or capture mechanism, it's secure if it's obscure." That will buy an iota of time.

The other way is to simply not trust the host and end-to-end encrypt everything important. This is a PITA, but there is no current viable alternative without a significantly rigorous and extensive project (would be in the form of a VM for servers &| something that runs on js like asm.js)

Mostly you need zero knowledge computation. Storage and network are easier probs.

The intractable problem is eventually an answer needs to be presented somewhere. For now, you should minimize exposure as much as possible through all means available.

[tptacek]

None of this comment has anything to do with my comment. If you don't want to use RDRAND, compile a kernel that doesn't.

[ballard]

To avoid hobgoblins wearing Faraday cages without denying the reality of the privacy debate, open source hw can make them quieter. I think it's going to happen because of PC market forces (IBM/Lenovo, Dell) and prior examples (OpenSparc). The startup costs (eda, test equipment) are doable because there are enough people with specialized expertise that could contribute.

If you don't trust the hw or vhost, you're stuffed. Political upwards and technical downwards are the ways to make sure this doesn't happen.