Comment by austin-cheney
4 days ago
This is broken logic.
There is an untested assumption that hashes achieve randomness because they appear to be a random collection of characters. Hash sequences are completely reproducible given a set of input, and that is by definition not random.
I think you are confusing loss of prediction as randomness. Never in mathematics or logic is that line of thinking correct. This can be described by equivocation, fallacy of composition, inductive fallacy, and more.
I think you are mixing the function itself and it's output, if for a given input to the function the output is uniformly random, then this is a way to derive randomness. The fact that the function itself is deterministic tells you nothing about the distribution of it's output.
You started your comment with a correct distinction, but got the wrong conclusion. Asking if somthing is random is actually a question about the process used to obtain some value and not the value itself. If I ask you if 42 is a random number, can you actually answer? I can get that number with an intrinsically random process based on some quantum effect, or I can say it from the top of my head because I just read a very famous book. You can indeed use an hash function to extract randomness, but, to be precise, we are talking about pseudo-randomness. The crucial difference here is that, if I'm measuring photons' polarization to get a random number, then an attacker repeating the same process will (very likely) obtain a different number. If I'm instead hashing some data, an attacker passing the same data through the same hash function will get the same result. Another example: if I hash the digits of pi, I will get a sequence that will pass statistical tests for randomness. But an attacker that knows how I am generating such sequence can easily reproduce it.
> There is an untested assumption that hashes achieve randomness because they appear to be a random collection of characters.
lol, no. Cryptographic hash functions are specifically designed to achieve this property.
> Never in mathematics or logic
Let's not get ahead of ourselves. Start with English - what does "pseudo" mean?
> This can be described by equivocation, fallacy of composition, inductive fallacy, and more.
For example, what is a pseudo-intellectual?
> lol, no. Cryptographic hash functions are specifically designed to achieve this property.
That completely ignores the definition of the word random.
What I find most interesting about this thread of comments is that the article explains the failure of using hashes as a means of randomness and despite that failure people are eager to ignore what hashes are otherwise used for to invent oppositional arguments. it's weird.
It's a lot less weird if you consider the possibility that you don't understand this as well as you think, and the reason people are consistently correcting you is because you are mistaken.
he said pseudo-randomness
And this still wrong for the same reasons. See: https://news.ycombinator.com/item?id=44521194
You're saying something being reproducible implies that it is not pseudo-random. This is a definition of pseudo-random that exists only in your head.
The first sentence of the wikipedia entry on pseudo-randomness is:
"A pseudorandom sequence of numbers is one that appears to be statistically random, despite having been produced by a completely deterministic and repeatable process."
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