53 research outputs found
Conditionals in Homomorphic Encryption and Machine Learning Applications
Homomorphic encryption aims at allowing computations on encrypted data
without decryption other than that of the final result. This could provide an
elegant solution to the issue of privacy preservation in data-based
applications, such as those using machine learning, but several open issues
hamper this plan. In this work we assess the possibility for homomorphic
encryption to fully implement its program without relying on other techniques,
such as multiparty computation (SMPC), which may be impossible in many use
cases (for instance due to the high level of communication required). We
proceed in two steps: i) on the basis of the structured program theorem
(Bohm-Jacopini theorem) we identify the relevant minimal set of operations
homomorphic encryption must be able to perform to implement any algorithm; and
ii) we analyse the possibility to solve -- and propose an implementation for --
the most fundamentally relevant issue as it emerges from our analysis, that is,
the implementation of conditionals (requiring comparison and selection/jump
operations). We show how this issue clashes with the fundamental requirements
of homomorphic encryption and could represent a drawback for its use as a
complete solution for privacy preservation in data-based applications, in
particular machine learning ones. Our approach for comparisons is novel and
entirely embedded in homomorphic encryption, while previous studies relied on
other techniques, such as SMPC, demanding high level of communication among
parties, and decryption of intermediate results from data-owners. Our protocol
is also provably safe (sharing the same safety as the homomorphic encryption
schemes), differently from other techniques such as
Order-Preserving/Revealing-Encryption (OPE/ORE).Comment: 14 pages, 1 figure, corrected typos, added introductory pedagogical
section on polynomial approximatio
Search for the most stable massive state in superstring theory
In ten dimensional type II superstring, all perturbative massive states are
unstable, typically with a short lifetime compared to the string scale. We find
that the lifetime of the average string state of mass M has the asymptotic form
T < const.1/(g^2 M). The most stable string state seems to be a certain state
with high angular momentum which can be classically viewed as a circular string
rotating in several planes ("the rotating ring"), predominantly decaying by
radiating soft massless NS-NS particles, with a lifetime T = c_0 M^5/g^2.
Remarkably, the dominant channel is the decay into a similar rotating ring
state of smaller mass. The total lifetime to shrink to zero size is ~ M^7. In
the presence of D branes, decay channels involving open strings in the final
state are exponentially suppressed, so the lifetime is still proportional to
M^5, except for a D brane at a special angle or flux. For large mass, the
spectrum for massless emission exhibits qualitative features typical of a
thermal spectrum, such as a maximum and an exponential tail. We also discuss
the decay properties of rotating rings in the case of compact dimensions.Comment: 24 pages, 1 figure. Correction on lifetime of average stat
Cross sections for production of closed superstrings at high energy colliders in brane world models
In brane world string models with large extra dimensions, there are processes
where fermion and antifermion (or two gluons) can annihilate producing a light
particle (e.g. gluon) carrying transverse momentum and a Kaluza-Klein graviton
or an excited closed string that propagates in the extra dimensions. In high
energy colliders, this process gives a missing momentum signature. We compute
the total cross section for this process within the context of type II
superstring theory in the presence of a D brane. This includes all missing
energy sources for this string theory model up to s=8M_s^2, and it can be used
to put new limits on the string scale M_s.Comment: 18 pages, 3 figures. Reference adde
Self-interacting fundamental strings and black holes
We study the size distribution of very massive close string states and the
typical string configuration as one slowly increase the string coupling, both
in the case of zero and of non-zero Neveu-Schwarz charges. The computations are
performed rigorously in string theory, starting from quantities that are
well-defined in the theory and therefore clarify previous works on the subject
which were based on various approximation techniques.
We find that, starting from a value of the coupling in agreement with the one
predicted by the black hole correspondence principle, the string ensemble is
dominated in any dimensions by compact states whose size is within the
correspondent black hole horizon radius, which is of the order of the string
scale at the black hole/string transition point.Comment: 31 pages plus references, final version accepted for publicatio
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