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The Futility of Lava Lamps: What Random Means

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Re: The Futility of Lava Lamps: What Random Means

#41

Post by tptacek »

Terr_ wrote: post #39
tptacek wrote: post #37

Earlier quoted context omitted.

In the immortal words of a cryptographic folk hero, if H(x, y) produces a good random number, H(x, y, z) will produce a number at least as good.

Perhaps you missed where I mentioned a constant "budget of bits." Your second h(x,y,z) is implicitly using more bits in the calculation, rather than "sharing" with x. In other words, these are the two functions that should be compared: h(content, very_random_bits(32)) h(content, very_random_bits(16) + slightly_random_bits(16))

The point of CSPRNG constructions is that there isn't a "budget bits" of seed. Again: this idea is pretty core to the design of the LRNG.

Neither of your constructions is secure.

Re: The Futility of Lava Lamps: What Random Means

#42

Post by [deleted] »

tptacek wrote: post #37
Terr_ wrote: post #35

Earlier quoted context omitted.

I'm not sure what you mean, deterministic hashing does not create more entropy than you started with. Lower-quality inputs means lower-quality results. You only want to use low-quality sources if the good stuff is too scarce or expensive. Imagine that tomorrow some reaction caused all those lava-lamps to cloud over into pure, constant, and uniform milky white. What effect would that have? It would make the system at…

In the immortal words of a cryptographic folk hero, if H(x, y) produces a good random number, H(x, y, z) will produce a number at least as good.

[deleted]

Re: The Futility of Lava Lamps: What Random Means

#43

Post by Terr_ »

tptacek wrote: post #41
Terr_ wrote: post #39

Earlier quoted context omitted.

Perhaps you missed where I mentioned a constant "budget of bits." Your second h(x,y,z) is implicitly using more bits in the calculation, rather than "sharing" with x. In other words, these are the two functions that should be compared: h(content, very_random_bits(32)) h(content, very_random_bits(16) + slightly_random_bits(16))

The point of CSPRNG constructions is that there isn't a "budget bits" of seed. Again: this idea is pretty core to the design of the LRNG. Neither of your constructions is secure.

To paraphrase how I see things going so far, plus one:

1. tptacek: "It's hard to imagine how Cloudflare's lava-lamps could ever make the cryptography worse."

2. Terr_: "Well, technically it could make it worse, if 'hey look we're using a cool lava-lamp wall' comes at the expense of opportunities to insert higher-quality entropy from some other source."

3. tptacek: "It doesn't matter because they can just add it to everything else."

4. Terr_: "I didn't say adding, I said substituting."

5. tptacek: "A CSPRNG algorithm always lets you add more passes and bits. You don't have to make that choice."

6. Terr_: "But Cloudflare does have to make that choice because sensors and computers and CPU-cycles and budgets are all limited! Those constraints are the entire reason we're even using a CSPRNG in the first place."

Re: The Futility of Lava Lamps: What Random Means

#45

Post by TZubiri »

dheera wrote: post #29
AlotOfReading wrote: post #9

Earlier quoted context omitted.

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.

> and the camera output is fed into snip snip ?

If your attack vector is breaking and entering, that's a pretty effective cybersecurity mechanism.

But even if it happened, this is one of many additive entropy mechanism, removing or controlling only one source would not be sufficient for any attack.

Re: The Futility of Lava Lamps: What Random Means

#46

Post by tptacek »

Terr_ wrote: post #43
tptacek wrote: post #41

Earlier quoted context omitted.

The point of CSPRNG constructions is that there isn't a "budget bits" of seed. Again: this idea is pretty core to the design of the LRNG. Neither of your constructions is secure.

To paraphrase how I see things going so far, plus one: 1. tptacek: "It's hard to imagine how Cloudflare's lava-lamps could ever make the cryptography worse." 2. Terr_: "Well, technically it could make it worse, if 'hey look we're using a cool lava-lamp wall' comes at the expense of opportunities to insert higher-quality entropy from some other source." 3. tptacek: "It doesn't matter because they can just add it to ev…

I'm sorry, I've lost track of what you're trying to argue. The point is that in practice, any sane design is just going to hash "lava lamp" information in with all the other low-quality entropy inputs that drive the LRNG. I wasn't making a subtle or complicated point here.

Re: The Futility of Lava Lamps: What Random Means

#47

Post by Terr_ »

tptacek wrote: post #46
Terr_ wrote: post #43

Earlier quoted context omitted.

To paraphrase how I see things going so far, plus one: 1. tptacek: "It's hard to imagine how Cloudflare's lava-lamps could ever make the cryptography worse." 2. Terr_: "Well, technically it could make it worse, if 'hey look we're using a cool lava-lamp wall' comes at the expense of opportunities to insert higher-quality entropy from some other source." 3. tptacek: "It doesn't matter because they can just add it to ev…

I'm sorry, I've lost track of what you're trying to argue. The point is that in practice, any sane design is just going to hash "lava lamp" information in with all the other low-quality entropy inputs that drive the LRNG. I wasn't making a subtle or complicated point here.

I'm not making a subtle or complicated point either. I think the start of it is that we had different ideas of what "worse" was being compared to.

You're saying "It's hard to tell a story where the wall is making things worse [compared to replacing it with nothing]." If the initially-unspoken bracketed condition is added, then yes, I agree with you.

My response was: "There might be a story where the wall is making things worse, compared to other things."

Re: The Futility of Lava Lamps: What Random Means

#48

Post by atoav »

geerlingguy wrote: post #2

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.

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.
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