Quote from: devphp on November 18, 2014, 08:41:46 PM

Quote from: phillipsjk on November 18, 2014, 08:23:37 PM

Unless I am mis-understanding, anybody with at least 50% stake can do that.

With PoW mining, a 51% attacker can not force you to stop mining (short of seizing or bombing your equipment).

Please explain.

This feels like a trap question. Transparent Forging is not implemented yet. For the sake of argument I decided to look at the link explaining how it works. It turns out that Come-from-Beyond is actually on my ignore list (due to general nonsense posts rather than sig advertising). The paper he cites is from 2011, and describes PoS, not "transparent forging" (and then does not go into detail). Here is CFB's description of the process:

Quote from: Come-from-Beyond on December 09, 2013, 09:58:22 AM

And the most important feature:
The network can detect which miners don't take part in block generation and act accordingly.

The last point deserves to be described with more details.

Imagine someone is going to do a "51%" attack against Nxt and he owns 90% of all coins. The adversary must stop generating blocks for legit branch coz he won't be able to compete against 100% mining power with his 90%. So he decides to "skip" his turn to generate a block. The rest 10% of the network detects this and penalizes the adversary by setting his mining power to 0 and distributing it among other miners. Now the network is back to 100% power coz everyone got 10-fold increase. The adversary can mine other branch in a secret place but it won't be able to replace the legit branch. Of course, the 2nd branch will have 100% "hashing" power tied to it as well, coz the attacker will get his 90% bumped to 100% but this can be counteracted by some mechanisms of advanced consensus (still not revealed).

I fail to understand why an attacker has to choose which chain to participate in. CFB never explains this. If I had 50% stake, I can say "la,la,la I can't hear you!" and pretend all other participants are offline.

Quote

Why do you have status "Sold 50% due to mining concentration." then below your username?

Because Ghash.io did not understand that they were becoming a central point of failure. Under coercion they (with the majority of the hash-power) would be able to:

prohibit unknown (with no ownership information) keys from spending BItcoin
ignore blocks from other miners.

While other miners can counteract this by buying hash-power, it takes time. Some have argued that a lot of pooled hash-power can actually switch loyalties relatively quickly. However, it is not clear how much hash-power Ghash.io has in-house.