Extension block proposal by Jeffrey et al

Summary:

In a Bitcoin development mailing list, Olaoluwa Osuntokun analyzed the xblock proposal and focused on the sub-proposal for Lightning Network (LN) safety enhancement. The LN risk system of blockchain availability in case of channel disputes is a recurring attack in this type of system. The xblock proposal includes a sub-proposal for LN which is essentially a block-size decrease for each open channel within the network. This decrease reserves space in blocks to allow honest parties guaranteed space in the blocks to punish dishonest channel counter parties. As a result, the block size is permanently decreased for each channel open. This solution was referred to as Pre-Allocated Smart-contract Dispute arena (PASDA).Transactions that mark the commencement of a smart contract whose security depends on the availability of block space for disputes are able to pre-allocate a section of the block that will always be reserved for dispute transactions. In this way, contracts are guaranteed space in blocks to handle disputes if the contract breaks down. However, the system has not been fully specified and evaluated yet.The proposed PASDA (Pre-Allocated Smart Contract Battling Arena) seeks to address one of the systematic risks in Lightning Network by eliminating the DoS vector attack, but at a high cost. The proposal requires smart contract transactions to set a certain bit in their version number to pre-allocate N bytes in all further blocks until the contract has been reserved. The proposed extension block (xblock) must not replicate the sighash bug and requires the scriptSig to always be empty, which leaves room for 7 future soft-fork upgrades to relax DoS limits. There are 16 unused witness program versions, and the witness script hash v0 shall be worth the number of accurately counted sigops in the redeem script, multiplied by a factor of 8.To implement this within Bitcoin, a third utxo set must be maintained by all full nodes. The author suggests a rent-based model where participants of the contract must pay a tribute to miners to account for their loss in revenue due to the reduction in block size. PASDA itself could fill up an entirely distinct proposal by itself spanning several pages.The email thread discusses various technical details related to the proposed extension block feature in Bitcoin. The Coinbase outputs are not allowed to contain witness programs as they cannot be swept by the resolution transaction due to previously existing consensus rules. The genesis resolution transaction can include a special message through pushdata in the first input script, which must be castable to a true boolean. The resolution transaction's version must be set to the uint32 max. Transactions within the extended transaction vector may include a witness vector using BIP141 transaction serialization. The proposed extension block activation entails BIP141 activation. Extension blocks leverage several features of BIP141, BIP143, and BIP144 for transaction opt-in, serialization, verification, and network services, and as such, extension block activation entails BIP141 activation. The xblock proposal includes a sub-proposal for LN which is essentially a block-size decrease for each open channel within the network. This decrease reserves space in blocks to allow honest parties guaranteed space in the blocks to punish dishonest channel counter parties. As a result, the block size is permanently decreased for each channel open. In conclusion, the proposal is seen as an academic topic rather than something ready for production use. The author suggests further analysis of the sub-proposal in detail and discusses its construction as well as its implications on smart-contracts like payment channels on top of Bitcoin. PASDA purports to address one half of the systematic risks in LN by possibly eliminating the DoS vector attack against LN. However, the costs of PASDA are very high, and possibly prohibitively so.

Updated on: 2023-06-11T23:35:52.232810+00:00