International Association
for Cryptologic Research

In this talk, we will describe how we use Multiparty Computation (MPC) to bridge a significant gap in the Account Aggregator (AA) framework in India. Briefly, AA is a regulated Open Finance framework in India that enables users to authorize licensed entities to view their financial information, in order to receive financial services. The AA ecosystem already has tens of millions of users, but suffers a gap in trust: financial data once revealed for one purpose (eg. applying for a loan) may be duplicated and reused by third parties for unauthorized purposes. We present a solution wherein user data is instead secret shared amongst a consortium of independent non-colluding parties, so that they may reveal only explicitly consented functions upon it via MPC. Our solution is designed to be a drop-in replacement—i.e. fully compatible with existing AA standards so that it can be used out of the box—and is currently being deployed by leading financial institutions and digital public infrastructure bodies. The talk will establish what is to our knowledge a new use case for MPC, and explore the technical challenges we faced in designing such a system to be compatible with existing "MPC-unfriendly" standards.

We study network-agnostic {\it secure multi-party computation} (MPC) in the presence of {\it computationally-bounded} adversaries. A network-agnostic protocol provides the best possible security guarantees, irrespective of the type of underlying communication network. Previous MPC protocols in this regime either assume a setup for a common reference string (CRS) and a threshold additively homomorphic encryption (Blum et al. CRYPTO 2020) or a plain public-key infrastructure (PKI) setup (Bacho et al. CRYPTO 2023). Both these MPC protocols perform circuit-evaluation over encrypted data and also deploy different forms of zero-knowledge (ZK) proofs, along with other computationally-expensive cryptographic machinery. We aim to build an MPC protocol based on circuit evaluation on secret-shared data, {\it avoiding} ZK proofs and other computationally-expensive cryptographic machinery and based on a {\it plain} PKI setup. To achieve our goal, we present the {\it first} network-agnostic {\it verifiable secret sharing} (VSS) protocol with the {\it optimal} threshold conditions, which is of independent interest. Previously, network-agnostic VSS is known either with {\it perfect} security (Appan et al. IEEE IT 2023) where the threshold conditions are {\it not} known to be optimal or with {\it statistical security} (Appan et al. TCC 2023) where the threshold conditions are optimal, but the parties need to perform {\it exponential} amount of computation and communication. Although our proposed MPC protocol incurs higher communication complexity compared to state-of-the-art network-agnostic MPC protocols, it offers valuable insights and motivates alternative directions for designing {\it computationally inexpensive} MPC protocols, based on a plain PKI setup, which has not been explored in the domain of network-agnostic MPC.