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Vinokur said in an interview that Terra Quantum’s team made the discovery after figuring out how to invert what’s called a “hash function,” Can someone comment

Vinokur said in an interview that Terra Quantum’s team made the discovery after figuring out how to invert what’s called a “hash function,” Can someone comment if “invert” really means invert or if it means an instant way of brute forcing all possible/probable inputs. Isn’t there an infinite number of inputs that produce the same hash, thus inverting a hash function would produce infinite results? Edit: forgot hashing usually truncates the payload to the 4096 characters/etc so I guess the inputs are finite.

whatshisface 6y ago
It's easy enough to ask for something like "the shortest string that hashes to this," or "what do I have to append to my string to make it hash to that." But you have a good point, there is no unique answer to inverting a hash - you need additional criteria for there to be one answer.
umvi 6y ago
> Isn’t there an infinite number of inputs that produce the same hash, thus inverting a hash function would produce infinite results? Well you only need to find a solution, you don't need to find all solutions (of which there are infinite as you say). Brute force is the only known way currently of discovering a solution, but perhaps Terra Quantum figured out some sort of "shortcut" that reduces the time to find a solution for a particular hash function. Until they release more details I'm highly skeptical you could quickly find a solution to something like sha256
- warkdarrior 6y ago
  In practice you to find a meaningful solution, i.e., it has to have the right structure/format. If I'm trying to hack your email (whatever that means), the solution would need to look like a valid email message, with reasonable headers and in the expected language.
- tppiotrowski 6y ago
  > Well you only need to find a solution, you don't need to find all solutions You're right! It doesn't matter that I don't know your actual password. Any text that hashes to the same value will work in the "password" input field.
nolite 6y ago
It means creating an algorithm which suggests a highly probable input that provides a given output. Check out Grover's Algorithm

whatshisface 6y ago

It's easy enough to ask for something like "the shortest string that hashes to this," or "what do I have to append to my string to make it hash to that." But you have a good point, there is no unique answer to inverting a hash - you need additional criteria for there to be one answer.

umvi 6y ago

> Isn’t there an infinite number of inputs that produce the same hash, thus inverting a hash function would produce infinite results? Well you only need to find a solution, you don't need to find all solutions (of which there are infinite as you say). Brute force is the only known way currently of discovering a solution, but perhaps Terra Quantum figured out some sort of "shortcut" that reduces the time to find a solution for a particular hash function. Until they release more details I'm highly skeptical you could quickly find a solution to something like sha256

warkdarrior 6y ago
In practice you to find a meaningful solution, i.e., it has to have the right structure/format. If I'm trying to hack your email (whatever that means), the solution would need to look like a valid email message, with reasonable headers and in the expected language.
tppiotrowski 6y ago
> Well you only need to find a solution, you don't need to find all solutions You're right! It doesn't matter that I don't know your actual password. Any text that hashes to the same value will work in the "password" input field.

nolite 6y ago

It means creating an algorithm which suggests a highly probable input that provides a given output. Check out Grover's Algorithm