njohnson41
Joined 12 years ago
Joined 12 years ago
But, I'm pretty sure the assumptions of logistic regression are even stronger than just that. The inputs are assumed to be independent given the output class, and the log odds of the output vary as a linear function of each input. The first one is essentially the naive Bayes assumption, and the second one is completely unreasonable for almost any problem ever (roughly equivalent to assuming every dataset has a multivariate normal distribution). If they are both correct, though, you get a perfectly good Bayesian posterior probability of each output class.
I think the lesson is that gradient descent will build a decent function approximation out of pretty much anything powerful enough, which is why neural networks still work even when probability theory has been thrown completely out the window.
Neural network outputs are not probabilities. I think that's the main lesson here.
I think the correct way to state it is: "all true statements are either tautologies, or can be determined empirically (with arbitrarily high but not necessarily measure-1 probability)". This statement is itself a tautology, because tautologies are by definition true, and because "determined" implies some method of determination, which if it actually can be used to determine truth, means it can be used empricially. Determination and empiricism are secretly defined in terms of each other, basically. The reason this tautology is worth stating is that it gives a simple criterion for discarding non-questions: questions that have no method of determining whether they are true or false (with arbitrarily high probability), are always non-questions.
Just like 42, "atoms and the void" here is just a science-flavored attempt to answer a non-question.
Yes, but this doesn't even come close to describing the typical users' password, which is most likely a 6-letter English word with a capital letter and a 1! appended to the end. Your calculation here isn't really relevant, because it's all about the worst or common case. (You also assume that people are using a GPU for a compute-bound problem, when much faster FPGAs are also available, but either way it's moot.)
Security through obscurity, which is what you're proposing with the shuffled salt idea, is also not normally considered the right way to go. If you wanted to use a similar but much simpler and straightforward method, you could just encrypt the salted hashes before storing them in the database.
The one case where they coincide (sort of) is if you believe your random sequence is generated by a randomly chosen Turing machine, which I've only really seen in philosophical settings.
A uniformly chosen 64-bit integer still has exactly 64 bits of entropy, regardless of how much Kolmogorov complexity the actual bits you generate have.
A deterministic PRNG's sequence has exactly the entropy of it's seed, actually, but it has 0 bits of entropy per symbol, because its sequence is infinite.
The thing most people get confused about with entropy is in thinking that entropy is a property of some single object, like a bit string. Really, entropy is always a measurement about a probability distribution, just like mean or variance is. In the usual case with random streams, the distribution is P(x_i | x_i-1 ... x_0) for bits x_i in the stream, i.e. the distribution remaining for the current bit even if we know all previous bits. For a deterministic PRNG, once we can extract the key from the history (given unlimited compute power) that distribution becomes deterministic, so the entropy is 0.
This has always been possible, but it sounds like they've lowered the minimum entropy needed in the source streams to produce a high-quality output.
So, now it has jumped from (disk -> network -> memory -> ...) to (network -> disk -> memory -> ...), which is a big change.