I’m conscious that, theoretically talking, there isn’t any strategy to assure {that a} reversed hash is definitely what’s inputted to the hashing operate. Nevertheless, to illustrate that I’ve a picture, I write down the file dimension of that picture after which run it by means of the SHA-256 hashing algorithm. I then distribute the hash to all the ~6.5 billion smartphones on our planet, together with the preliminary file dimension. How lengthy would it not take for all smartphones in existence on earth to completely brute pressure a SHA-256 hash, not like Bitcoin the place you solely should reverse a few of it?

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  • An Apple M1 CPU can do round 2 GB/s of SHA256 (based mostly on the optimized 2-way hardware-accelerated ARMv8 code in Bitcoin Core added in PR24115) on a single core.
  • Smartphones are considerably slower than M1 laptop computer CPUs resulting from energy utilization limitations, however let’s ignore that, and conservatively overestimate each smartphone has a hexacore CPU that may do that a lot, so 12 GB/s per machine in whole.
  • SHA256 operates on blocks of 64 bytes. Let’s assume that the attacker picks a set prefix, after which simply must grind the final 64 bytes + padding (one additional block) of the file. In order that they’re simply hashing 128 bytes. (12 GB/s) / 128 B ≈ 94 million tries per second, per machine.
  • 6.5 billion units instances which means 6×1017 information per second in whole.
  • Each file try has a chance of two-256 of yielding an accurate preimage. Meaning one wants within the order of two256 tries to have an affordable probability of discovering a preimage.
  • 2256 / 6×1017 ≈ 2197 seconds
  • The age of the universe is round 13.7 billion years, or 258.5 seconds.
  • Thus the assault would take round 2197 / 258.5 ≈ 400000000000000000000000000000000000000000 instances the age of the universe.