http://txngrid.com/txngrid.pdf
Proposal for securing blockchain without resorting to computing power.
- Use a separate crypto-currency to track the voters and their voting power.
- A fixed number of representatives are selected deterministically for each block based on the hash of the voter's public key, his voting power, and the previous block hash.
- The selected representatives sign the blocks using their private key.
The blockchain is double linked by the block hash and the voter signatures. The probability of attack is very low no matter how far the attackers go back in history. It can take 10,000 years for attackers to be successful even they control 50% of the voting power.