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Perfectly secure steganography using minimum entropy coupling

arxiv.org

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Re: Perfectly secure steganography using minimum entropy coupling

#21
post #19

Earlier quoted context omitted.

Right, so in total ignorance what I would do is just make a GPT powered text compressor and decompressor using a range coder with its probabilities at each token set by the model. Care would need to be taken with precision and end termination so a bias wouldn't be introduced (more care than typical in compressors, since no one normally cares much about 0.01% inefficiencies-- things like end termination have been addr…

Hi, I am one of the authors on the PSSuMEC paper. Thanks a lot for your interest in our work. If I understand correctly, range coding would have the same lack of perfect security properties as arithmetic coding (cf our paper). Having said this, we are investigating the utility of iMEC in compression settings.

Ah, yeah I was trying to get a lay explanation of how arithmetic coding assuming it was done with enough precision wouldn't achieve the perfect security properties.

It might just be that the precision rapidly becomes unmanageable, because I guess you need to support the least probable symbol from every token without ever losing precision (normally arithmetic coders will re-normalize after each symbol to keep the accumulator in a reasonable precision, though they could be designed to do so as infrequently as you like at a performance cost)... If no renormalization is possible I guess an arithmetic coder accumulator would need to handle values like (1/least_prob_token)^n_tokens which gets extremely big extremely fast -- and would at the very least need an unconventional construction.

Re: Perfectly secure steganography using minimum entropy coupling

#22
post #16

Earlier quoted context omitted.

> I suppose that under authoritarian regimes you will soon have to cryptographically prove that you generated your random bits deterministically from specific keys I guess that's sarcasm but I don't really get it. Just in case you mean it, that doesn't seem even remotely technically doable to me. And even if you managed to make people generate all randomness from a fixed PRNG with key escrow, you would have to check…

While I'm sure it is sarcastic it's worth noting that most (all?) blockchain wallets already do this. Technically it's in reverse: the seed is random and then serialized into a human readable seed phrase but the deterministic key generation is already widely deployed. https://en.bitcoin.it/wiki/Deterministic_wallet

There is even code to code secrets into grammars with perfect uniformity. https://github.com/sipa/gramtropy

But it only works on specially constructed grammars and not LLMs. :)

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