Multi-Section Fault Proof Game: Catch-all Discussion + Q&A

[qizhou]

Goal

The objective of the proposal is to develop a multi-section fault-proof game on top of the existing bisect FaultDisputeGame.sol with minimal changes. The idea is to use EIP-4844 BLOB to carry 4096 claim/state hashes in each move(). As a result, countering a claim by calling a move() can create 4096 sub-claims with the following features:

• The number of move() calls to complete a game is expected to reduce from 73 (MAX_DEPTH of Sepolia testnet) to 7 (3*12=36 for SPLIT_DEPTH, and 4*12=48 for EXECUTION_DEPTH). The potential main benefit will be a significant gas reduction for the challenger over the whole game and a reduction in fault proof window.
• We expect the additional gas cost of move() will be minimal: the additional fee will be mainly BLOB fee for each move(). This is done by reusing existing data structures, e.g., in each move(), the claim hash is replaced by the hash of sub-claims - resulting in no additional storage cost.
• The code changes to FaultDisputeGame.sol will be minimized, and the existing definitions such as Position, Depth, MIPS.sol, etc will be retained. Further, the N-section fault-proof game would subsume bisect FaultDisputeGame.sol when N=2. Therefore, all existing tests (unit tests, e2e tests) for FaultDisputeGame.sol can be also used to test the new multi-section fault-proof game.

Materials

• Proposal
• Draft Spec
• Code in progress

[qizhou]

Some updates on our multi-section fault dispute game (FDG) progress:

• Given the testnet FDG gas cost https://sepolia.etherscan.io/tx/0xb92621eb9ea7b2e9c57962041a9158ee318dd011237e290209b820bf4b6a9510, we summarize the expected moves and reduced gas cost using multi-section FDG:

	Moves	Per move gas cost	Total gas
Current (N = 2)	73	~250,000 (link)	~18,250,000
N = 16 with calldata	19	~258,192	~4,905,648
N = 256 with calldata	10	~381,072	~3,810,720
N = 4096 with calldata	8	~2,347,152	~18,777,216
N = 4096 with EIP-4844	8	~250,000	~2,000,000
N = 16384 with EIP-4844	7	~250,000	~2,000,000

• We gave a talk at EthPrague about the proposal on June 2, 2024. The official stream link is here https://www.youtube.com/watch?v=vbCSqdB-D8g
• We have implemented LibDA.sol - a general library to support DA (calldata / EIP-4844 / others) for different multi-section claim hashes https://github.com/ethstorage/optimism/pull/29/files
• We completed a draft multi-section DFG Support Nary=4, draft version ethstorage/optimism#31, which is compatible with N = 2 case.

Future actionable plans:

• Add 4-section DFG tests
• Add EIP-4844 DA support

[dajuguan]

Major updates on Multi-Section Fault Dispute Game (FDG) from EthStorage team:

Completed Enhancements:

• Fully Featured Multi-Section DFG: We've successfully integrated a multi-section fault dispute game(DFG) with minimal code modifications to FaultDisputeGame.sol.
• Key Migrations in FaultDisputeGameN.sol:
  • Migrated step() to stepV2()
  • Migrated attack() and defend() to attackV2().
  • Adapted addLocalData to support adding subClaims of the attacking Claim.
• Internal Function Adaptations:
  • _findStartingAndDisputedOutputRoots
  • _verifyExecMultisectionRoot
  • _findExecTraceAncestor
  • _findTraceAncestorV2
  • _findTraceAncestorRoot

Completed Testing for 4-Section DFG
Implemented and passed all test cases in the original FaultDisputeGame.t.sol. We've also added and successfully tested new edge cases, see ethstorage/optimism#40 ethstorage/optimism#41