Private information retrieval (PIR) allows a client to query a public database privately and serves as a key building block for privacy-enhancing applications. Minimizing query size is particularly important in many use cases, for example, when clients operate on bandwidth-constrained devices. However, existing PIR protocols exhibit large query sizes: to query 225 records, the smallest query size of 14.8 KB is reported in Respire [Burton et al., CCS24]. Respire is based on fully homomorphic encryption (FHE), where a common approach to lower the client-to-server communication cost is transciphering. When combining the state-of-the-art transciphering [Bon et al., CHES24] with Respire, the resulting protocol (which we refer to as T-Respire) has a 336 B query size, while incurring a 16.2x times higher server computation cost than Respire. Our work introduces a novel alternative to transciphering for reducing the client-to-server communication: the client transmits only one component of a high-precision LWE ciphertext, from which we design a modular procedure to extract the inputs for the subsequent homomorphic computation. The efficiency of this approach is demonstrated by our Pirouette protocol, which achieves a query size of just 36 B. This represents a 9.3x reduction compared to T-Respire and a 420x reduction to Respire. For queries over 225 records, the single-core server computation in Pirouette is only 2x slower than Respire and 8.1x faster than T-Respire, and the server computation is highly parallelizable. Furthermore, Pirouette requires no database-specific hint for clients, and its variant PirouetteH enables additional tradeoffs among query size, throughput, and offline communication, demonstrating the flexibility of our design

The outbreak of the COVID-19 pandemic has changed our lives in unprecedented ways. In the face of the projected catastrophic consequences, most countries have enacted social distancing measures in an attempt to limit the spread of the virus. Under these conditions, the Web has become an indispensable medium for information acquisition, communication, and entertainment. At the same time, unfortunately, the Web is being exploited for the dissemination of potentially harmful and disturbing content, such as the spread of conspiracy theories and hateful speech towards specific ethnic groups, in particular towards Chinese people and people of Asian descent since COVID-19 is believed to have originated from China.