The definition of the one way function says:
- it must be verifiable in polynomial time
- probability of inverting it less or equal to negligible
Now, I am not sure I fully understand one way functions.
- Can I say that $f(x) = x$ is a one way function?
- Do we assume that we know how $f$ is defined?
- if $x$ is of length $l$, then the probability of guessing it is: $(1/2)^l$ which is negligible.
I am pretty sure that my reasoning is wrong, any hint?