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Toward practical and private online services
Today's common online services (social networks, media streaming, messaging,
email, etc.) bring convenience. However, these services are susceptible to
privacy leaks. Certainly, email snooping by rogue employees, email server
hacks, and accidental disclosures of user ratings for movies are some
sources of private information leakage. This dissertation investigates the
following question: Can we build systems that (a) provide strong privacy
guarantees to the users, (b) are consistent with existing commercial and policy
regimes, and (c) are affordable?
Satisfying all three requirements simultaneously is challenging, as providing
strong privacy guarantees usually necessitates either sacrificing functionality,
incurring high resource costs, or both. Indeed, there are powerful cryptographic
protocols---private information retrieval (PIR), and secure two-party
computation (2PC)---that provide strong guarantees but are orders of magnitude
more expensive than their non-private counterparts. This dissertation takes
these protocols as a starting point and then substantially reduces their costs
by tailoring them using application-specific properties. It presents two
systems, Popcorn and Pretzel, built on this design ethos.
Popcorn is a Netflix-like media delivery system, that provably hides, even from
the content distributor (for example, Netflix), which movie a user is watching.
Popcorn tailors PIR protocols to the media domain. It amortizes the server-side
overhead of PIR by batching requests from the large number of concurrent users
retrieving content at any given time; and, it forms large batches without
introducing playback delays by leveraging the properties of media streaming.
Popcorn is consistent with the prevailing commercial regime (copyrights, etc.),
and its per-request dollar cost is 3.87 times that of a non-private system.
The other system described in this dissertation, Pretzel, is an email system
that encrypts emails end-to-end between senders and intended recipients, but
allows the email service provider to perform content-based spam filtering and
targeted advertising. Pretzel refines a 2PC protocol. It reduces the resource
consumption of the protocol by replacing the underlying encryption scheme with a
more efficient one, applying a packing technique to conserve invocations of the
encryption algorithm, and pruning the inputs to the protocol. Pretzel's costs,
versus a legacy non-private implementation, are estimated to be up to 5.4 times
for the email provider, with additional but modest client-side requirements.
Popcorn and Pretzel have fundamental connections. For instance, the
cryptographic protocols in both systems securely compute vector-matrix products.
However, we observe that differences in the vector and matrix dimensions lead to
different system designs.
Ultimately, both systems represent a potentially appealing compromise: sacrifice
some functionality to build in strong privacy properties at affordable costs.Computer Science
Primer: Fast Private Transformer Inference on Encrypted Data
It is increasingly important to enable privacy-preserving inference for cloud
services based on Transformers. Post-quantum cryptographic techniques, e.g.,
fully homomorphic encryption (FHE), and multi-party computation (MPC), are
popular methods to support private Transformer inference. However, existing
works still suffer from prohibitively computational and communicational
overhead. In this work, we present, Primer, to enable a fast and accurate
Transformer over encrypted data for natural language processing tasks. In
particular, Primer is constructed by a hybrid cryptographic protocol optimized
for attention-based Transformer models, as well as techniques including
computation merge and tokens-first ciphertext packing. Comprehensive
experiments on encrypted language modeling show that Primer achieves
state-of-the-art accuracy and reduces the inference latency by 90.6% ~ 97.5%
over previous methods.Comment: 6 pages, 6 figures, 3 table
Verifiable Encodings for Secure Homomorphic Analytics
Homomorphic encryption, which enables the execution of arithmetic operations
directly on ciphertexts, is a promising solution for protecting privacy of
cloud-delegated computations on sensitive data. However, the correctness of the
computation result is not ensured. We propose two error detection encodings and
build authenticators that enable practical client-verification of cloud-based
homomorphic computations under different trade-offs and without compromising on
the features of the encryption algorithm. Our authenticators operate on top of
trending ring learning with errors based fully homomorphic encryption schemes
over the integers. We implement our solution in VERITAS, a ready-to-use system
for verification of outsourced computations executed over encrypted data. We
show that contrary to prior work VERITAS supports verification of any
homomorphic operation and we demonstrate its practicality for various
applications, such as ride-hailing, genomic-data analysis, encrypted search,
and machine-learning training and inference.Comment: update authors, typos corrected, scheme update
Trusted Execution Environments in Protecting Machine Learning Models
The adaptation and application of machine learning (ML) has grown extensively in recent years, and has awakened concern about the safety of intellectual property (IP) related to the machine learning models. The training of machine learning models is a time-consuming and expensive task, that has increased the demand of better solutions to protect the intellectual property of the machine learning models. This thesis explores the promising potential of Trusted Execution Environments (TEE) like Intel's Software Guard Extensions (Intel SGX), in protecting intellectual property related to machine learning models. The concern of ML model safety arises especially when the software solution needs to be distributed to clients or machine learning operations needs to be done in an untrusted environment. The main focus of this thesis is on Intel's SGX, which is one of the most used TEE implementations. This thesis tries to answer to the questions on how TEEs can be used to protect IP of the ML models, what aspects need to be considered and what limitations may arise
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