Rex Fernando

I’m a cryptographer. Since 2023 I’ve been at Aptos Labs, where I work on the practice of cryptography. Previously, I did a PhD at UCLA with Amit Sahai and a postdoc at Carnegie Mellon with Aayush Jain and Elaine Shi, working on the theory of cryptography — secure multiparty computation, zero-knowledge arguments, obfuscation.

There is a large gap between those two things, and most of what I do now involves trying to bridge this gap: taking primitives that were known to be possible and making them efficient enough to run during a consensus protocol.

I’m based in New York. Email me at rex1fernando@gmail.com.

Encrypted mempool

I led the effort to build the first encrypted mempool deployed on an L1. An encrypted mempool is a new technology that prevents malicious extractive behavior targeting pending transactions. It does this by allowing users to encrypt their transaction payloads before submitting, and then doing decryption directly on the nodes of the network via a threshold-shared secret key after the transaction is part of a committed block.

Doing this naively via standard threshold encryption would involve a prohibitive amount of overhead. We solved this using an exciting new primitive called batched threshold encryption (BTE). We constructed the first practical BTE scheme in ePrint 2024/1575. Our subsequent work, TrX, improves upon this scheme and gives the first integration of an encrypted mempool with a high-performance BFT protocol. It costs 27 ms of proposal-to-execution latency, a 14% overhead over the unmodified baseline. Our system is live on the Aptos network!

A new non-interactive DKG

Besides the new BTE scheme, the other major building block for our encrypted mempool is a brand-new non-interactive distributed key generation (DKG) protocol. In order to coincide with the proof-of-stake majority assumption of the network, a new secret key for the system must shared at the epoch boundary, i.e., every time the nodes’ stake weights change. This is done via a DKG. A non-interactive DKG differs from standard interactive protocols, in that the key for the next epoch can be generated by the nodes in the current epoch. This means the epoch change logic is much simpler, and causes a much faster epoch-start.

We implemented what is probably the largest-scale non-interactive DKG in production in order to power encrypted mempool. At its core is a new, fast ZK range proof called DeKartProof. Along with some new techniques for DKG message dissemination, this new range proof enabled us to scale to a full L1-sized setting with over a hundred stake-weighted nodes.

Publications / Preprints

Batched threshold encryption

  • TrX: Encrypted Mempools in High Performance BFT Protocols. Rex Fernando, Guru-Vamsi Policharla, Andrei Tonkikh, Zhuolun Xiang. SBC 2026. ePrint 2025/2032 — Deployed on Aptos
  • Efficiently-Thresholdizable Batched Identity Based Encryption, with Applications. Amit Agarwal, Rex Fernando, Benny Pinkas. CRYPTO 2025, SBC 2025. ePrint 2024/1575

Zero-knowledge arguments

  • Couplet: Multivariate Polynomial Commitments with Two-Group-Element Openings. Weijie Wang, Alin Tomescu, Rex Fernando, Charalampos Papamanthou. ePrint 2026/2106

  • DekartProof: Efficient Vector Range Proofs and Their Applications. Dan Boneh, Trisha Datta, Rex Fernando, Kamilla Nazirkhanova, Alin Tomescu. SBC 2025. ePrint 2025/1159 — a univariate version is deployed on Aptos as part of the DKG for encrypted mempool

  • Distributed-Prover Interactive Proofs. Sourav Das, Rex Fernando, Ilan Komargodski, Elaine Shi, Pratik Soni. TCC 2023. doi

  • Account ZK-Rollups from Sumcheck Arguments. Rex Fernando, Arnab Roy. CCS 2023 (poster). doi

  • Statistical ZAP Arguments. Saikrishna Badrinarayanan, Rex Fernando, Aayush Jain, Dakshita Khurana, Amit Sahai. EUROCRYPT 2020. ePrint 2019/780

Secure multiparty computation

  • Two-Round Concurrent 2PC from Sub-exponential LWE. Behzad Abdolmaleki, Saikrishna Badrinarayanan, Rex Fernando, Giulio Malavolta, Ahmadreza Rahimi, Amit Sahai. ASIACRYPT 2023. ePrint 2022/1719
  • Maliciously-Secure MrNISC in the Plain Model. Rex Fernando, Aayush Jain, Ilan Komargodski. EUROCRYPT 2023. ePrint 2021/1319
  • Maliciously Secure Massively Parallel Computation for All-but-One Corruptions. Rex Fernando, Yuval Gelles, Ilan Komargodski, Elaine Shi. CRYPTO 2022. ePrint 2022/1027
  • Secure Massively Parallel Computation for Dishonest Majority. Rex Fernando, Ilan Komargodski, Yanyi Liu, Elaine Shi. TCC 2020. ePrint 2020/1157

Obfuscation and witness encryption

  • Output Compression, MPC, and iO for Turing Machines. Saikrishna Badrinarayanan, Rex Fernando, Venkata Koppula, Amit Sahai, Brent Waters. ASIACRYPT 2019. ePrint 2018/866
  • Preventing CLT Attacks on Obfuscation with Linear Overhead. Rex Fernando, Peter M. R. Rasmussen, Amit Sahai. ASIACRYPT 2017. ePrint 2016/1070

Distributed agreement and anonymity

  • Scalable Distributed Agreement from LWE: Byzantine Agreement, Broadcast, and Leader Election. Rex Fernando, Yuval Gelles, Ilan Komargodski. ITCS 2024. doi
  • Non-Interactive Anonymous Router with Quasi-Linear Router Computation. Rex Fernando, Elaine Shi, Pratik Soni, Nikhil Vanjani, Brent Waters. TCC 2023. ePrint 2022/1395

Thesis

  • Stronger Round-Optimal Secure Protocols without Setup. UCLA, 2022. eScholarship

Earlier work

Before cryptography I worked in computational number theory at UW Madison and in programming languages at Iowa State. Some publications from that past life:

  • Infinitely Many Carmichael Numbers for a Modified Miller-Rabin Prime Test. Eric Bach, Rex D. Fernando. ISSAC 2016, 47–54. doi · arXiv:1512.00444
  • Modular Reasoning in the Presence of Event Subtyping. Mehdi Bagherzadeh, Robert Dyer, Rex D. Fernando, José Sánchez, Hridesh Rajan. LNCS Transactions on Modularity and Composition 2016, 167–223 (doi); conference version MODULARITY 2015, 117–132 (doi)
  • Event Type Polymorphism. Rex D. Fernando, Robert Dyer, Hridesh Rajan. FOAL 2012, 33–38. doi
  • Modularizing Crosscutting Concerns with Ptolemy. Hridesh Rajan, Sean L. Mooney, Gary T. Leavens, Robert Dyer, Rex D. Fernando, Mohammad Ali Darvish Darab, Bryan Welter. OOPSLA Companion 2011, 31–32. doi
  • SNPlotz: A Generic Genome Plot Tool to Aid the SNP Association Studies. Zhi-Liang Hu, Rex Fernando, Dorian Garrick, James M. Reecy. BMC Bioinformatics 11(S4):P4, 2010. doi

Elsewhere

Email · IACR ePrint · GitHub · DBLP

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