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Comment by loup-vaillant | Hacker News Reader

We stop before the key is big enough to requires the energy of our sun to crack, even if you have an ideal computer. 256-bit keys require more energy than a nova.

128 bits however is humanly achievable (35 years worth of peak Bitcoin mining), and as such perhaps a tad low in really high stakes scenarios (say highly classified stuff).

We could chose something between 128 and 256, but they're nice powers of two, and we tend to like powers of two.

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To enumerate 128 bits in 35 years you would need to make 3e29 attempts per second.

Current bitcoin miner can provide efficiency of 19 000 000 MH/J or 19e12 H/J. If we would assume bruteforcer can perform with the same efficiency, we would need 1.6e16 J/s = 16 000 TW.

Current humanity energy output is something like 17 TW.

Yeah, botched my numbers, sorry. I saw that the hash rate of the current Bitcoin network went up to 2^93 hashes per year, and then I managed to pretend 2^128/2^93 = 35, instead of 2^35.

With your numbers if humanity dedicated all its energy to brute forcing a 128/bit key for a year it would have a ~0.1% chance of finding it. I guess that's a pretty good argument that no one is going to even try it in the foreseeable future.

See this cousin comment highlighting my error. that out: https://news.ycombinator.com/item?id=34955855

I got billions of years when I used the current bitcoin hashing rate for 128 bits. Are you assuming a birthday attack?

No, I just botched it and pretended 2^35 = 35. See these other comments for more details:

https://news.ycombinator.com/item?id=34955855

https://news.ycombinator.com/item?id=34963094

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