I am the CTO of a new DPOS project called SWAPBlocks. We have recently shifted our DPOS blockchain from Lisk source code to Ark. We had planned to have an initial 101 delegates, but some of the members of the discord channel have said they prefer 51 due to the quicker block times.
When systems are "semi-decentralized" the risk is very clear. Regarding that with 101 more people have a chance to forge, with 51 you need 26 of 51 to make a successful attack, but you will need 51 malevolent delegates to fully confirm with 101. It is the case that more people would need to agree to succeed on an attack.
Considerations:
1. You have to evaluate the real risk of your delegates agreeing on a 51% attack. Are they institutional delegates with clear ownership that are less likely to get themselves into trouble or does the system really need to be completely trustless with a huge degree of "distrust". If you delegates are not really likely to agree on an attack and are identifiable, you can probably do with less.
2. When planning a 51% attack each of the 26 delegates would need to trust the other 25 because if they fail on their attack they will loose their stakes, thus...How high are the stakes? How much risk will those malevolent nodes have for themselves if they try an attack?
3. On a the practical side: If you are going to make it from 3 days or 6 months to 1 minute, does it matter if it takes 2 minutes (or 4 or 5) for your particular case? Normally I would say no unless you are planning an exchange, and in that case you most likely need a centralized component on the system.
4. What time confirmation differences you have with 50, 100 and 200 delegates? Have you made accurate numbers?
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