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The $5000 Compression Challenge (2001)

(www.patrickcraig.co.uk)
181 points ekiauhce | 1 comments | 23 Nov 24 21:10 UTC | HN request time: 0s | source
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ccleve ◴[23 Nov 24 23:55 UTC] No.42224858[source]▶
I wonder if it would have been possible to win the challenge legitimately?

If a randomly-generated file happened to contain some redundancy through sheer chance, you could hand-craft a compressor to take advantage of it. This compressor would not work in general for random data, but it could work for this one particular case.

It's a bet worth taking, because the payoff, 50:1 ($5,000 to $100), is pretty good. Play the game 50 times and you might get a file you could compress.

The challenge, then, would be for the person offering the bet to generate a really random file that contained no such redundancy. That might not be easy.

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Retr0id ◴[24 Nov 24 00:34 UTC] No.42225057[source]▶
Somewhere (discussed on HN) someone devised a "better-than-perfect" compressor. Most inputs get compressed (smaller than input), except for one input that does not. That one input is cryptographically impossible to find - or something along those lines.

Unfortunately I can't find the article I'm describing here, maybe someone else can? It was a long time ago so I might be misrepresenting it slightly.

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1. phire ◴[25 Nov 24 02:49 UTC] No.42232781[source]▶
It can't exist.

Presume this compressor guarantees the output will always be at least one byte smaller (with the exception of the impossible to find input)

So just keep running your data in a loop through the compressor. If you start with a 1MB file, it will take a maximum of a million iterations until the output shrinks down to zero bytes, which is the smallest possible file. Record how many iterations it too.

You can now extract your file by feeding a zero byte file into the decompressor and running the same number of iterations. Which You can now store every 1MB (or smaller) file in the world in just 20 bits.... But that would means there are only 1 million possible 1MB files?

Even if you put some minimum output size limitation on the compressor, say it can't produce any file less than 512 bits, the same argument applies. It's just that the numbers get bigger.