[cejast]

> One feature that cryptocurrencies gain from their decentralised computing design is that they become very robust to potential attacks from national governments.

I was always under the impression that they would be more susceptible to attacks from national governments, since they'll have greater access to the resources needed for a 51% attack.

[gopalv]

> more susceptible to attacks from national governments

The attacks don't need to be on the currency, it can be on the privacy.

The ledger is like a giant warrantless paper-trail of who paid whom.

As a side-note, how would I reject a payment that came through bitcoin?

If I were an unscrupulous government who wanted to target an individual, I'd just send them some money from a suspicious account and then bring them in for questioning over that payment.

[CuriousCosmic]

So to my knowledge you can't choose to not accept a transaction but you can always send the transaction back to the sender.

[TchoBeer]

I think both parties have to sign a transaction.

[CuriousCosmic]

This is not the case at least on most major networks.

On UTxO (Unspent Transaction Output) based networks the transaction is signed by the sender and generates new UTxO for each recipient. The UTxO aren't signed by the recipient but they can be redeemed by the recipient using their private keys (as the UTxO is either signed by or derived from the recipient's public key/address). If you wanted to "return" the funds you'd just create a transaction containing the received UTxO as an input and deduct whatever fees that are used in the Tx from said UTxO. This "returns" the Tx without you spending any funds or having "kept" any amount of their funds.

On the Account/Balance model I believe the way it works is similar. The sender signs the Tx with their private key and the receiver signs the Tx with their public key. In this case the "return" Tx is just going to involve sending the fund amount back to the sender since there isn't any separation of Tx outputs in the account balance.

[sauwan]

Maybe my wallet does that automatically, but that has not been my experience.

[mort96]

Yeah, China accounts for around 65% of Bitcoin mining globally. If they ever wanted to, I assume they could coerce many of their biggest miners to cooperate on a 51% attack.