The Futility of Lava Lamps: What Random Means

https://loup-vaillant.fr/articles/lava-lamps-and-randomness

by birdculture • 2 months ago

77 57 2 months ago

I don't remember their initial post about the lava lamps, but I had assumed that was a marketing gimmick more than anything... a neat visual way to convey what entropy is in a way normal humans can comprehend.

It's certainly not a scalable solution for entropy, and there are so many ways for it to fail as a sole source, as well.

dheera2• 2 months ago

I'm dead sure they aren't using them for anything.

This is SF. If they were really used for anything, a random dude in a black hoodie and white SUV can just smash the glass and take down the internet, and the SF police wouldn't do a thing.

kgeist• 2 months ago

If you look up videos on YouTube, you'll see that they allow visitors to stand between the lava lamps and the cameras (sometimes even entire groups!). And I've always wondered: doesn't that reduce entropy, since people usually wear monotone clothing? And if the lamps are so important, why would they allow that? Maybe the lamps do contribute something, but their system most likely already generates enough entropy with or without the lamps...

AlotOfReading2• 2 months ago

Smashing the glass wouldn't make it less effective. The sensor itself has noise, and the camera output is fed into an HMAC with a key based on the current nanosecond before being combined with a traditional entropy source before it ever went anywhere. Even then, it was only used as a seed for the entropy pool on the actual server.

Gh0stRAT• 2 months ago

It's been quite a while since I first heard about it, but IIRC they were seeding cryptographic PRNGs with entropy from multiple sources, one of which was allegedly this art installation.

Seeding PRNGs with sufficiently unpredictable data was a real security concern for a while. New cloud instances have a small entropy pool space for attackers to enumerate due to lack of a real source of randomness. (See the Debian/OpenSSL issue for what can happen when your entropy pool is too small/predictable)

One fun fact about XOR is that anything XOR'd with a uniform random distribution results in a uniform random distribution, so there isn't any harm in mixing additional non-attacker-controlled entropy sources in as long as at least one of them is sufficiently unpredictable. The lava lamps provide a potentially hard-to-predict source of entropy for this, but if it's not available then it certainly doesn't "take down the internet". They'll still use packet arrival timing, interrupt timing, etc to seed their CSPRNGs.

atoav• 2 months ago

If you want entropy ot is trivial to construct a white noise source that gives you flat white noise over a range of a few MHz using the reverse avalanche breakdown of a zener diode. The harder part is then reading that out in a way that doesn't introduce bias and makes use of the bandwidth, but if tou want random it is right there in electronic quantum processes.

JKCalhoun5• 2 months ago

With a one-time pad being, as I understand it, the only really good encryption, I am surprised there is not a market for pairs of matched hard drives—the pair having the same "one time pad" stored on them (how you generate those numbers is left as an exercise for the company marketing them).

A simple app could be used by parties on both ends of the message—an app that relies on an associated drive to act as the pad.

If you become aware that one of the two matched drives has been compromised (stolen perhaps by an outside party), you destroy its partner.

(Perhaps too you can design the drive in such a way as to make it non-trivial to copy—you more or less need possession of the drive itself. That makes it unlikely for there to be a 3rd drive the two parties are unaware of.)

marshray2• 2 months ago

I've heard it said that such systems may be used by militaries, where they have an organizational structure naturally-suited to large keystream distribution.

Unlike e-commerce, it's no problem to physically send the proverbial officer handcuffed to a briefcase to the nuclear submarine before it submerges for 6 months.

Also the messages to be secured are, um, short and... infrequent.

JKCalhoun5• 2 months ago

I kind of assumed the "customer" here would in fact be government agencies…

AgentME• 2 months ago

Conventional symmetric cryptography is already very secure and easy, even in the face of future threats like quantum computers. (Asymmetric cryptography is the type of cryptography that cryptographers spend more time worrying about.) Not that you should do it yourself, but it's relatively easy to whip up a secure symmetric encryption scheme if you have a hash function that meets certain basic security properties (which even hash functions with known weaknesses like MD5 and SHA-1 still meet!). The only real hard part of symmetric cryptography is key management (making sure both ends of each conversation have the matching keys ready to use), and one time pads only make that harder by making the keys very large and stateful. I think there are few use-cases where the potentially increased security makes up for the more difficult key management (especially if it means you're also swearing off all asymmetric cryptography).

buildbot• 2 months ago

I think that post quantum encryption methods might be in this category but I am not knowledgeable enough to say either way.

One issue though with making a one time pad trivial to copy - how do you authenticate that you are allowed to read? How do you know the client isn’t copying?

b65e8bee43c2ed0• 2 months ago

the reason why there isn't a market for such drives is that someone who needs that level of security rightfully wouldn't trust any entity to

1. generate truly random data, which is required for OTP to be perfect

2. not store a copy of the data to be handed over to bioluminescent individuals at the drop of a hat

ykonstant• 2 months ago

bioluminescent individuals

Brilliant.

p1necone2• 2 months ago

Surely if you were that security conscious you'd never trust some third party to put the keys on the drives and not keep a copy for themselves - you'd just buy two regular drives and put the key on there yourself.

JKCalhoun5• 2 months ago

That's fine. I'm just not aware that even this is being done. But it seems to be pretty secure to being decrypted if captured in transit.

gizmo686• 2 months ago

One time pads are the only solution that is secure from an information theoretic perspective. In practice, however, that is not important. You would essentially be securing yourself against a weapon that no one has, and most experts think cannot actually exist.

DevelopingElk• 2 months ago

Russian one time pads were frequently broken. How? They were inconvenient to distribute, so people reused them.

Symmetric cryptography is safer because one key can easily protect as much data as you need.

JKCalhoun5• 2 months ago

I would think that a 10TB one-time pad (for example) would probably never get "used up".

rob-lag• 2 months ago

One-time pad has 2 problems:

(1) The key can only be used once. If you use the same key for multiple different messages it's not secure anymore.

(2) The key has to be the same length as the message.

With those 2 restrictions, OTP is not really that feasible for practical applications.

JKCalhoun5• 2 months ago

(1) The key can only be used once.

Sure, and I'm contemplating something like 10 TB of random data as key (I mean hard drives are large these days).

(2) The key has to be the same length as the message.

I thought that was just a matter of indexing through the (10 TB) of data with each message—picking up in the byte stream where you left off from your previous message.

Retr0id2• 2 months ago

And if it is broken… then you’re screwed, sorry. See, both your encryption and your CSPRNG relies on a cipher. If either is broken, then so is your whole system.

Not necessarily. The CSPRNG state could in theory be leaked via sidechannels. Your cipher key could be leaked via sidechannels too, but symmetric encryption keys tend to be shorter lived.

Retr0id2• 2 months ago

Another "why on earth are HN users downvoting this?" moment...

marshray2• 2 months ago

As far as cryptographic security theater goes, it's hard for me to get angry about lava lamps.

danparsonson• 2 months ago

They're very calming

the_red_mist• 2 months ago

article has a section dedicated to "how to obtain starting seed" with a list of examples and somehow fails to include wall of lava lamps in said list of examples

p1necone2• 2 months ago

They kind of do if you play 6 degrees of wikipedia...

The 'hardware random number generator' link in the list in the article goes to https://en.wikipedia.org/wiki/Hardware_random_number_generat..., and then in the see also section on that article there's a link to the page for a different lava lamp wall, with a photo of the cloudflare one: https://en.wikipedia.org/wiki/Lavarand

tptacek6• 2 months ago

They don't actually do anything, but I think it's hard to tell a story where they make things worse, given that Cloudflare is a cryptographically competent org. It's just getting mixed into the already-secure conventional CSPRNG they're using (almost certainly: just the Linux kernel RNG).

Terr_5• 2 months ago

I think it's hard to tell a story where they make things worse [...] mixed into the [...] CSPRNG

I think it's easy to tell a story where it's slightly worse. I mean, for any budget of storage bits and CPU cycles, any "inferior" random data necessarily pushes out "better" stuff.

tptacek6• 2 months ago

It's all hashed together. The whole LRNG design assumes most of its inputs are structured or poorly randomized.

glitchc2• 2 months ago

The lava lamps aren't being used as a CSPRNG, rather they constitute part of the seed for the CSPRNG.

tptacek6• 2 months ago

Yes, I get that.

__MatrixMan__2• 2 months ago

Nothing is random enough for an arbitrary audience. There's always the possibility that some alien spaceship will land and some creature will emerge, take a glance at your RNG, and say: "next one's 6598489811, try it" and they'll be right.

We can only say that something is random enough given a certain audience's beliefs about what kind of predictions are possible. If it takes lava lamps to convince that audience, well then ok.

NuclearPM• 2 months ago

Why would beliefs matter?

mock-possum• 2 months ago

Because the judgment of what counts as ‘enough’ is tied to beliefs

__MatrixMan__2• 2 months ago

Beliefs drive our actions, even when they're about unknowable things. Whether or not something is random is unknowable, so belief is all we have.

We may discover tomorrow that events which we previously thought were random, like the timing of a single atom's radioactive decay, are actually perfectly predictable. If we believe that such a discovery is unlikely then we might trust radioactive decay as an entropy source, and if we believe its very likely then we probably won't.

glitchc2• 2 months ago

I suspect the author hasn't heard of physical unclonable functions.

ticulatedspline• 2 months ago

Lotta speculation about it's value but seems cloudflare does legitimately use this source.

https://blog.cloudflare.com/lavarand-in-production-the-nitty...

They even mention it's origins in Lavarand (and LavaRand) the former which has an actual patent: https://patents.google.com/patent/US5732138A/en

Yes there's a bit of theater here, and they admit to using the sensor noise as well, it's also not their only source of physical entropy. While you could do just as much with less interesting sources the wall of lava lamps is a perfectly cromulent source of randomness, also is kinda fun.

delichon• 2 months ago

Lava lamp entropy embiggens us all.

dherls• 2 months ago

Seems needlessly angry about what is ultimately a decent if imperfect source of entropy, and a good illustrative example for the general public

jbritton• 2 months ago

The very end of the article says “They can keep them for decoration but servers must generate their own random numbers.” I thought the lava lamps were for this purpose.

ge96• 2 months ago

How about electrodes attached to a mushroom

teravor• 2 months ago

there is probably more entropy coming from the sensor noise of the camera facing the wall of lava lamps than in the random flow inside them.

if you block the camera you will get even more entropy.

bambax• 2 months ago

Obligatory Dilbert reference:

https://www.americanscientist.org/sites/americanscientist.or...

rini17• 2 months ago

And before you go on objecting that a physical true RNG remains better than a could-theoretically-be-broken CSPRNG, understand that your random output often must have no detectable bias to be secure. That means a distribution so uniform you can’t detect a bias even after analysing 2^64 samples.

Why not, actually? I would think simple and trivially auditable HW RNG with, say, only 0.9 bits of entropy per output bit (raw! no whitening) is preferable to "perfect" but fragile algorithm.

Anything that requires the randomness in practice has enough overhead so that the 90% good entropy is not a problem. Failures caused by wrong assumptions and complications are.

The Futility of Lava Lamps: What Random Means

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