Security and Privacy Seminar Series: Wenhao Zhang, "BitGC made (more)efficient."

Abstract: This talk presents our recent progress on one-bit-per-gate garbled circuits, including a set of optimizations that substantially improve both theoretical and practical efficiency. 

Garbled circuits with one-bit-per-gate communication were recently introduced by Liu et al. (BitGC, Eurocrypt 2025), Meyer et al. (Crypto 2025), and Ishai et al. (Crypto 2025). These works focus primarily on the theoretical communication complexity, leaving open questions about practical computational efficiency. To address this gap, we first eliminate key barriers to enable SIMD support for BitGC, leading to a substantial speedup in its homomorphic operations. Second, we demonstrate that XOR gates can be garbled without any communication, improving both efficiency and simplicity. Finally, we present a computationally efficient garbling scheme that requires zero communication for XOR gates and only 5 bits per AND gate. When applied to an AES-128 circuit, our fastest garbling scheme generates a garbled circuit of just 4KB in 2 minutes on a single CPU core. 

This talk is based on joint work with Hanlin Liu, Kang Yang, Wen-jie Lu, Yu Yu, Xiao Wang, and Chenkai Weng. 

Bio: Wenhao Zhang is a PhD student in computer science at Northwestern University, advised by Xiao Wang. His interests mainly lie in applied cryptography, with a focus on secure multi-party computation, fully homomorphic encryption, and hardware-accelerated cryptography.