Abstract: Threshold Multi-Party cryptographic protocols are crucial tools in security-critical distributed systems like blockchains and distributed Cyber-Physical Systems. Folklore literature employed Information-Theoretic cryptography to design protocols, which incurs a high communication cost. Subsequent literature improved communication costs using public-key cryptography; however, these protocols incur a large computational cost from expensive public-key operations, which inhibits scalability. We address this bottleneck by designing protocols using lightweight cryptography - cryptographic Hash functions and Symmetric Key Encryption. These primitives are 1000x faster than public-key-based primitives, and they are also friendly to the Post-Quantum world. However, as these tools lack the transcript homomorphism offered by public-key-based tools, we employ novel distributed computing techniques to limit the increase in communication compared to public-key-based protocols. In the talk, I will discuss three new protocols - a) HashRand (CCS 2024), an asynchronous random beacon protocol that produces a continuous stream of secure randomness, b) Velox (CCS 2025), an asynchronous Multi-Party Computation protocol that enables computation over private inputs, and c) an asynchronous Dynamic Proactive Secret Sharing protocol that enables blockchains with dynamic participation to maintain secrets. Through extensive experimental evaluation, we have demonstrated that our works (and other lightweight cryptography-based threshold cryptographic protocols) achieve at least two orders of magnitude performance improvement over prior public-key-based threshold cryptographic protocols for 100 parties, substantially enhancing scalability through computational efficiency.
Joint work: Saurabh Bagchi, Akhil Bandarupalli, Adithya Bhat, Xiaoyu Ji, Soham Jog, Aniket Kate, Chen-Da Liu-Zhang, Daniel Pöllmann, Michael Reiter, Yifan Song.
[Slides] Suggested reading: Velox: Scalable Fair Asynchronous MPC from Lightweight Cryptography (ia.cr/2025/1630)
