Published on: 2015-09-21T17:15:12+00:00
In an email conversation, Justus Ranvier raised several questions regarding the definition of honest and malicious miners, as well as the concept of the "best valid chain." He questioned whether extending the chain with an empty block is always a malicious act and whether a miner with 49% hashing power would be considered honest for doing the same. There were blind spots in distinguishing between honest and malicious blocks, and it was suggested that empty blocks indicate malice while rebroadcasted transactions from the mempool indicate honesty. The inability to distinguish between these blocks is a significant issue that needs to be addressed.A 51% attack occurs when the majority of mining power is controlled by malicious miners who can mine empty blocks on top of the best chain. Bitcoin relies on the majority of mining power being honest to function effectively. However, if a fork exists due to a disagreement in the network where mining power is split between two camps, each mining peacefully on their own chain, it is not problematic. Miners mining invalid blocks are no longer relevant to the Bitcoin consensus. Light clients face challenges in distinguishing between valid and invalid chains, but simple proofs could potentially solve this problem.Rune Kjær Svendsen proposed including UTXO set hashes in newly created blocks to allow new nodes to verify new transactions without retrieving the entire blockchain history. This would save bandwidth and ease the initial syncing process for Bitcoin Core nodes. While there are concerns about the security implications of relying on UTXO set commitments, Svendsen argues that it would not reduce the protocol's security.The discussions also touched on the scalability issues of validating the full blockchain history and ways to alleviate this burden for new nodes joining the network. One proposal suggests hashing the UTXO set and storing it on disk, along with a copy of the UTXO set at that time. This would increase the difficulty for an attacker with hidden hashing power to overwrite a year's worth of blocks. However, there are concerns that an attacker with over 50% of the network hashrate could rewrite history. Before considering mechanisms for UTXO set commitments, it is crucial to discuss the reasonableness of reducing the security model.Overall, the discussions highlighted the need to address the distinction between honest and malicious miners, the ability to distinguish between different types of blocks, the inclusion of UTXO set hashes in newly created blocks, and the potential implications for Bitcoin's security model. Patrick Strateman questioned the proposal to use UTXO set commitments, as it may reduce the current security model by allowing an attacker with more than 50% of the network hashrate to create an unlimited number of bitcoins. However, Svendsen suggested a solution where newly mined blocks include the UTXO set hash of the chain up until the previous block, which would save bandwidth and allow new nodes to acquire the UTXO set in a trustless manner. This approach maintains Bitcoin's security model while easing the initial syncing process for nodes.
Updated on: 2023-08-01T16:13:07.536002+00:00