UTT: Sensibly-Anonymous Decentralized Payments from
Rerandomizable Signatures
Alin Tomescu
Thursday, November 16, 2023
Talk at 4:00pm
Gates 259 & Zoom (https://stanford.zoom.us/j/92732897040?pwd=Q29JOFVFSy9kWXVDR3dIVWlGektFdz09)
Abstract:
We present UTT, a system for decentralized ecash with accountable
privacy.
UTT is the first ecash system that obtains three critical properties:
(1) it provides decentralized trust by implementing the ledger, bank,
auditor, and registration authorities via threshold cryptography and
Byzantine Fault Tolerant infrastructure; (2) it balances accountability
and privacy by implementing anonymity budgets: users can anonymously
send payments, but only up to a limited amount of currency per month.
Past this point, transactions can either be made public or subjected to
customizable auditing rules; (3) by carefully choosing cryptographic
building blocks and co-designing the cryptography and decentralization,
UTT is tailored for high throughput and low latency. With a combination
of optimized cryptographic building blocks and vertical scaling
(optimistic concurrency control), UTT can provide almost 1,000 payments
with accountable privacy per second, with latencies of around 100
milliseconds and less. Through horizontal scaling (multiple shards),
UTT can scale to tens of thousands of such transactions per second.
With 60 shards we measure over 10,000 transactions with accountable
privacy per second, with latencies around 500 milliseconds.
We formally define and prove the security of UTT using an MPC-style
ideal functionality. Along the way, we define a new MPC framework that
captures the security of reactive functionalities in a stand-alone
setting, thus filling an important gap in the MPC literature. Our new
framework is compatible with practical instantiations of cryptographic
primitives and provides a trade-off between concrete efficiency and
provable security that may be also useful for future work.
Bio:
Alin is a Cryptography Research Scientist at Aptos Labs. He received
his PhD from MIT in 2020.
Alin's research focus is on designing, proving and implementing new
cryptographic primitives for real-world use, focusing on authenticated
data structures, threshold cryptography and sensibly-anonymous payment
schemes.
Alin was previously a Research Scientist at VMware, where he mostly
worked on vector commitments and anonymous payments for central banking.
Before his PhD work, he was Head of Research & Development at Private
Machines, where he worked on building tamper-proof clouds.
Alin often muses about cryptography (and other fantastic beasts) over at
https://alinush.github.io/. His favorite thing in the world is
motorcycling through beautiful, sunny California while listening to
out-of-this-world music in the background.