[dirvine]

Rewarded POW has been an incredible defense against attack, including Sybil in bitcoin and POW derivatives. It has drawbacks though and therefore we now see a lot of research into revising older algorithms and enhancing these. This paper does that with a binary consensus algorithm and an adapted concrete coin (as opposed to a common coin/ threshold signature scheme)

There are many consensus algorithms that are not POW and they work perfectly fine, we cite some in the paper. Many require trusted nodes etc. and that is not so great, however, the work in this field of distributed consensus is increasingly popular. If you duckduckgo for BFT or PBFT algorithms and derivations you will find plenty. This one is very asynchronous and requires no trusted setup phase or threshold signature mechanism, making it an attractive choice.

In its plain form, as described then if you managed to get over 1/3 nodes on the network you could defeat consensus. Its use in SAFE is for valid voting nodes and then you would a much larger proportion than 1/3 of the network. Not only that, but they would have to be online and well behaved for longer than the existing network nodes. It is then much more expensive than a 1/3 attack.

Hope that helps.