Steven Goldfeder will present his Pre FPO on Monday, February 26, 2018 at 3PM in CS 302. The members of his committee are: Arvind Narayanan (adviser), Ed Felten, Mark Zhandry, and Matt Weinberg, Rosario Gennaro All are welcome to join. Abstract and title follow below. Increasing scalability and privacy for cryptocurrencies via off-chain protocols Abstract: The limits of Bitcoin’s scripting language motivate the need for off-blockchain protocols that extend the functionality of Bitcoin scripts. These protocols are run out-of-band by the transacting parties, but they are constructed in a manner that cryptographically binds them to on-chain scripts. Even with the advent of Ethereum, which provides a much richer scripting language, there are still privacy and scalability benefits to running off-chain protocols, even when on-chain analogs exist. I present off-chain protocols for a variety of applications as well as a general framework for off-chain smart contracts. An important tool for constructing off-chain protocols is threshold-signatures, a primitive that enables distributing the signing power of a given public key into n shares, such that at least k shares are required to produce a signature from that key. I show how to construct threshold signatures that are compatible with Bitcoin, and use this primitive to build off-chain protocols for privacy-preserving access control and escrow services. Turning to more advanced smart contracts, I show off-chain protocols for the fair exchange of digital goods and services for payment. Finally, we present a private and scalable smart contract system which enables arbitrary smart contracts that are enforced via off-chain protocols.