Machine learning tools have illustrated their potential in many significant
sectors such as healthcare and finance, to aide in deriving useful inferences.
The sensitive and confidential nature of the data, in such sectors, raise
natural concerns for the privacy of data. This motivated the area of
Privacy-preserving Machine Learning (PPML) where privacy of the data is
guaranteed. Typically, ML techniques require large computing power, which leads
clients with limited infrastructure to rely on the method of Secure Outsourced
Computation (SOC). In SOC setting, the computation is outsourced to a set of
specialized and powerful cloud servers and the service is availed on a
pay-per-use basis. In this work, we explore PPML techniques in the SOC setting
for widely used ML algorithms-- Linear Regression, Logistic Regression, and
Neural Networks.
We propose BLAZE, a blazing fast PPML framework in the three server setting
tolerating one malicious corruption over a ring (\Z{\ell}). BLAZE achieves the
stronger security guarantee of fairness (all honest servers get the output
whenever the corrupt server obtains the same). Leveraging an input-independent
preprocessing phase, BLAZE has a fast input-dependent online phase relying on
efficient PPML primitives such as: (i) A dot product protocol for which the
communication in the online phase is independent of the vector size, the first
of its kind in the three server setting; (ii) A method for truncation that
shuns evaluating expensive circuit for Ripple Carry Adders (RCA) and achieves a
constant round complexity. This improves over the truncation method of ABY3
(Mohassel et al., CCS 2018) that uses RCA and consumes a round complexity that
is of the order of the depth of RCA.
An extensive benchmarking of BLAZE for the aforementioned ML algorithms over
a 64-bit ring in both WAN and LAN settings shows massive improvements over
ABY3.