Private information retrieval (PIR) enables clients
to query and retrieve data from untrusted servers without the
untrusted servers learning which data was retrieved. In this
paper, we present a new class of multi-server PIR protocols,
which we call heterogeneous PIR (HPIR). In such multi-server
PIR protocols, the computation and communication overheads
imposed on the PIR servers are non-uniform, i.e., some servers
handle higher computation/communication burdens than the others. This enables heterogeneous PIR protocols to be suitable for a
range of new PIR applications. What enables us to enforce such
heterogeneity is a unique PIR-tailored secret sharing algorithm
that we leverage in building our PIR protocol.
We have implemented our HPIR protocol and evaluated its
performance in comparison with regular (i.e., homogenous) PIR
protocols. Our evaluations demonstrate that a querying client
can trade off the computation and communication loads of the
(heterogeneous) PIR servers by adjusting some parameters. For
example in a two-server scenario with a heterogeneity degree
of 4/1, to retrieve a 456KB file from a 0.2GB database, the
rich (i.e., resourceful) PIR server will do 1.1 seconds worth of
computation compared to 0.3 seconds by the poor (resource-constrained) PIR server; this is while each of the servers would
do the same 1 seconds of computation in a homogeneous setting.
Also, for this given example, our HPIR protocol will impose a
912KB communication bandwidth on the rich server compared
to 228KB on the poor server (by contrast to 456KB overheads
on each of the servers for a traditional homogeneous design).
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Batched Differentially Private Information Retrieval
Private Information Retrieval (PIR) allows several clients to query a database held by one or more servers, such that the contents of their queries remain private. Prior PIR schemes have achieved sublinear communication and computation by leveraging computational assumptions, federating trust among many servers, relaxing security to permit differentially private leakage, refactoring effort into an offline stage to reduce online costs, or amortizing costs over a large batch of queries.
In this work, we present an efficient PIR protocol that combines all of the above techniques to achieve constant amortized communication and computation complexity in the size of the database and constant client work. We leverage differentially private leakage in order to provide better trade-offs between privacy and efficiency. Our protocol achieves speedups up to and exceeding 10x in practical settings compared to state of the art PIR protocols, and can scale to batches with hundreds of millions of queries on cheap commodity AWS machines. Our protocol builds upon a new secret sharing scheme that is both incremental and non-malleable, which may be of interest to a wider audience. Our protocol provides security up to abort against malicious adversaries that can corrupt all but one party.
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- NSF-PAR ID:
- 10358604
- Date Published:
- Journal Name:
- 31st USENIX Security Symposium
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract In this work we demonstrate that allowing differentially private leakage can significantly improve the concrete performance of secure 2-party computation (2PC) protocols. Specifically, we focus on the private set intersection (PSI) protocol of Rindal and Rosulek (CCS 2017), which is the fastest PSI protocol with security against malicious participants. We show that if differentially private leakage is allowed, the cost of the protocol can be reduced by up to 63%, depending on the desired level of differential privacy. On the technical side, we introduce a security model for differentially-private leakage in malicious-secure 2PC. We also introduce two new and improved mechanisms for “differentially private histogram overestimates,” the main technical challenge for differentially-private PSI.more » « less
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Abstract We study both the practical and theoretical efficiency of private information retrieval (PIR) protocols in a model wherein several untrusted servers work to obliviously service remote clients’ requests for data and yet no pair of servers colludes in a bid to violate said obliviousness. In exchange for such a strong security assumption, we obtain new PIR protocols exhibiting remarkable efficiency with respect to every cost metric—download, upload, computation, and round complexity—typically considered in the PIR literature. The new constructions extend a multiserver PIR protocol of Shah, Rashmi, and Ramchandran (ISIT 2014), which exhibits a remarkable property of its own: to fetch a b -bit record from a collection of r such records, the client need only download b + 1 bits total. We find that allowing “a bit more” download (and optionally introducing computational assumptions) yields a family of protocols offering very attractive trade-offs. In addition to Shah et al.’s protocol, this family includes as special cases (2-server instances of) the seminal protocol of Chor, Goldreich, Kushilevitz, and Sudan (FOCS 1995) and the recent DPF-based protocol of Boyle, Gilboa, and Ishai (CCS 2016). An implicit “folklore” axiom that dogmatically permeates the research literature on multiserver PIR posits that the latter protocols are the “most efficient” protocols possible in the perfectly and computationally private settings, respectively. Yet our findings soundly refute this supposed axiom: These special cases are (by far) the least performant representatives of our family, with essentially all other parameter settings yielding instances that are significantly faster.more » « less
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Accepted Manuscript1.0
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