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Comment by klntsky | Hacker News Reader

> prevent anyone from hiding from the tax collectors and police

Only if you use chains with traceable transactions.

You also have to only buy things available purely on that system from people you are certain don’t collaborate with the government. If all of those assumptions aren’t true, your activity can be tracked with increasing precision and the authorities will see local transactions which you can’t explain otherwise and demand explanations.

The schemes Zcash and Monero use have never been tested at scale with a sophisticated adversary. The statistical methods used are probably fine for keeping your friends from knowing what you buy but it’s less clear that a government which can observe network traffic and receive KYC data from compliant merchants or compromised devices won’t be able to rule out some of the decoys over time, and since it’s a blockchain you’re gambling that this will hold true forever.

I like to think the government has a unique and sophisticated rubber-hose attack, just auditing you.

That’s one of the big questions here: if repressive governments are in your threat model, does a given system mean a normal person is likely to leave too much data on their devices? It’s really easy to imagine checks on all of the phones seized from protesters, anyone suspected of spending beyond their reported income, etc. so something which doesn’t make it really easy to purge old history is pretty risky - not least because if they catch you hiring anything there’s a nasty problem of convincing them that there’s nothing more still hidden.

> The schemes Zcash and Monero use have never been tested at scale with a sophisticated adversary

Monero's ring signatures are not the same as ZCash's zero-knowledge crypto. Monero obfuscates, but ZCash hides completely, cryptographically.

https://z.cash/learn/is-zcash-traceable/

That’s the hope anyway - even if the cryptography is perfect against all future attacks (remember they’ve already had at least one flaw in earlier versions) there are still things like timing attacks:

https://crypto.stanford.edu/timings/

Nation states are some of hardest attackers since they can do things like monitoring network traffic to correlate with chain activity or compel some fraction of the participants to surrender data. I know some smart people work on Zcash but there’s no safety net when all of the transactions are public and immutable.

I did not know this is possible - can You give an example of blockchain with this property?

zcash is one. https://en.m.wikipedia.org/wiki/Zcash

Monero, and zero-knowledge ones: zcash and more recent Mina which supports smart contracts.

It's incredible how often we must refer to this classic xkcd when talking about crypto "security": https://xkcd.com/538/

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