In collaboration with: M. Moosavi (OffchainLabs/Concordia), M. Salehi (OffchainLabs), D. Goldman (OffchainLabs).

Optimistic rollups like Arbitrum and Optimism are in wide use today as an opt-in scalability overlay ("L2") for blockchains like Ethereum. In this talk, we propose methods for sidestepping two practical pain-points for users of optimistic rollups: (1) withdrawing ETH takes 7 days (a "withdrawal window") to allow disputes before finalizing, and (2) withdrawing ETH to L1 requires the user to first have ETH on L1 to pay gas fees. Our solution involves making withdrawals ("exits") tradeable before they are finalized so they can be bought and sold for ETH that is already finalized on Ethereum. We propose prediction markets to insure exits and consider how tradeable exits should be priced. We implement and test the changes in the bridge/outbox of Arbitrum Nitro, the most used L2. The main takeaway is that anyone on L1 (users or contracts) can safely accept withdrawn tokens while the dispute period is still open despite having no knowledge of what is happening on L2. 

Jeremy Clark is an associate professor at the Concordia Institute for Information Systems Engineering. At Concordia, he holds the NSERC/Raymond Chabot Grant Thornton/Catallaxy Industrial Research Chair in Blockchain Technologies. He obtained his PhD from the University of Waterloo, where his gold medal dissertation was on designing and deploying secure voting systems including Scantegrity -- the first cryptographically verifiable system used in a public sector election. He wrote one of the earliest academic papers on Bitcoin, completed several research projects in the area, and contributed to the first textbook. Beyond research, he has worked with several municipalities on voting technology and testified to both the Canadian Senate and House finance committees on Bitcoin. Website: pulpspy.com.

Host: Alan T. Sherman, sherman@umbc.edu. Support for this event was provided in part by the National Science Foundation under SFS grant DGE-1753681. The UMBC Cyber Defense Lab meets biweekly Fridays 12-1pm.  All meetings are open to the public. Upcoming CDL meetings: August 29, CSEE Lightning Talks and Lab Open Houses, 9-11am, Lecture Hall VII (ITE-204); September 29 (exceptional date); October 6; October 20, (1-2pm, exceptional time); November 3, (1-2pm, exceptional time); November 17, (1-2pm, exceptional time); December 1.