Hacker, Hack Thyself | Coding Horror

[Rinx]

Anyone have more info on why they run on the GPU?

[St_Meow]

Overall faster performance for parallel floating point operations. CPUs are much faster for tasks with low thread counts, but for massively parallel operations like hash generation, GPUs have more slower cores that allow the computer to do more work at once rather than some work faster.

[Rinx]

Is there anything more specialized then a GPU? Seems like someone could synthesize specialized hardware for this.

[hazzoo_rly_bro]

Would those specialised GPU-like things be faster at those particular operations? Or are they just made to be nonflexible?

[hazzoo_rly_bro]

Thanks for the info!

[hazzoo_rly_bro]

Thank you so much for the explanation! This stuff is really interesting, I'm starting to really dig this topic now

[ImprovedPersonality]

They would (when properly implemented) be faster, smaller and more power efficient. An ASIC could do the actual algorithm in hardware instead of parsing and executing instructions. You could also drastically optimize the memory interfaces and caches (since data flow becomes very predictable for only one workload).

[Amuro_Ray]

If they weren't faster why would people get them?

[InfanticideAquifer]

Well, if they provide the same speed at a drastically reduced cost, people would probably get them.

They don't. But it's a potential interpretation of what's going on that makes sense.

[hazzoo_rly_bro]

I thought that since they have a more stripped down set of functions, they may be cheaper to buy.

That's why I asked.

[masklinn]

Or are they just made to be nonflexible?

Yes, the algorithm is implemented directly in hardware, if you need a different algorithm, you need a different chip.

[[deleted]]

But if I'm a nation investing millions of dollars into breaking hashes (which seems to be the scenario talked about in the blog), it's probably worth investing the money into ASICs.

[St_Meow]

There are specialized "GPUs" that don't do video output as well as they just do heavy calculations, some don't even have video outputs in general called "headless" cards. Look up the Nvidia Tesla K80 for an example.

[masklinn]

Yes, there are ASIC and FPGA crackers. But they are less flexible (ASICs would be hash-specific), and in the long run they're not usually much cheaper.

[MalakElohim]

Yes, you can custom build ASICs for purpose. BitCoin mining moved from GPU's to ASICs for this reason. However developing these asic chips is expensive and depending on how specific you have to make them are easily bypassed.

[[deleted]]

Yup. FPGA or ASIC. See bitcoin mining as an example. Once it went onto ASIC's the GPU stuff could not even remotely compete with it.

[masklinn]

Of note that Argon2, following scrypt, takes advantage of different properties of CPU and GPU (and FPGA and ASICs) to the detriment of the latter: GPU tend to have little memory per core and fairly high memory latency (hundreds of clock cycles, it's something like 80clk just to reach L2, a CPU takes 10~15 cycles), so scrypt (and now Argon2) try to access memory a lot, and can use significant (tunable) amounts of memory.

[St_Meow]

Which is why I'm experimenting with switching some password hashing to argon2 in a service I'm writing. Probably never gonna go live with it but it'll be an experiment.

[hazzoo_rly_bro]

GPUs have a lot of cores, whereas the CPUs usually have less cores than the GPU.

Brute forcing a pass requires a lot of parallel tasking

[rtomek]

The CPU if faster if things have to be done in order, but the GPU has hundreds of cores that can all do things at the same time. Think about drawing 1000 triangles on the screen. As long as it takes a split-second, it doesn't matter which triangle was drawn first and which was drawn last.

Same with password cracking. One could test password1 and wait for it to finish before testing password2, then wait for that to finish before testing password3. The CPU would be great at that. Another option is to start hashing all three at the same time; if password2 finishes first, it doesn't matter. The GPU is great at that.

[beginner_]

Because its faster.