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A common drawback of secure vector summation protocols in the single-server model is that they impose at least one synchronization point between all clients contributing to the aggregation. This results in clients waiting on each other to advance through the rounds of the protocol, leading to large latency (or failures due to too many dropouts) even if the protocol is computationally efficient. In this paper we propose protocols in the single-server model where clients contributing data to the aggregation (i) send a single message to the server and (ii) can join aggregation sessions dynamically whenever they have resources, i.e., without the need for synchronizing their reporting time with any other clients. Our approach is based on a committee of parties that aid in the computation by running a setup phase before data collection starts, and a verification/decryption phase once it ends. Unlike existing committee-based protocols such as Flamingo (S\&P 2023), the cost for committee members can be made sub-linear in the number of clients, and does not depend on the size of the input client vectors. Our experimental evaluation shows that our protocol, even while allowing dynamic client participation, is competitive with the state of the art protocols that do not have that feature in both computation and communication.

Abstract not available.

While non-black-box techniques suffice to establish theoretical feasibility, black-box constructions are often the gold standard for achieving modularity, efficiency, and broad applicability. The MPC-in-the-head paradigm not only revealed a surprising and elegant connection between secure multiparty computation (MPC) and zero knowledge (ZK), but also narrowed the gap between black-box and non-black-box constructions for serveral cryptographic primitives. In this talk, I will explore how the pursuit of black-box approaches has raised interesting theoretical questions while simultaneously enabling the development of some of the fastest and most scalable MPC and ZK systems to date. I will present several of our recent real-world implementations developed at our startup, including:

1) A maliciously secure, dishonest-majority MPC protocol supporting 10,000 parties for distributed RSA key generation;
2) A protocol capable of executing 1,000 auctions in parallel among 60 parties in under 5 minutes; as well as scheduling a meeting between 3 or more parties!
3) A developer-friendly ZK framework so intuitive and portable, we can vibe code from a mobile phone!

These results highlight how black-box cryptography can power both rigorous theory and practical innovation at scale.

Ads measurements require to privately join advertisement impressions and conversions and aggregate them across billions of users. We have implemented a three party honest majority MPC system based on the secure evaluation of the DY PRF, shuffle, vectorized Boolean operations and distributed ZKPs. We scale tested the system across 3 parties with 50 shards each, processing a total of 2 billion impressions and conversions.