1,782 research outputs found
A Survey on Homomorphic Encryption Schemes: Theory and Implementation
Legacy encryption systems depend on sharing a key (public or private) among
the peers involved in exchanging an encrypted message. However, this approach
poses privacy concerns. Especially with popular cloud services, the control
over the privacy of the sensitive data is lost. Even when the keys are not
shared, the encrypted material is shared with a third party that does not
necessarily need to access the content. Moreover, untrusted servers, providers,
and cloud operators can keep identifying elements of users long after users end
the relationship with the services. Indeed, Homomorphic Encryption (HE), a
special kind of encryption scheme, can address these concerns as it allows any
third party to operate on the encrypted data without decrypting it in advance.
Although this extremely useful feature of the HE scheme has been known for over
30 years, the first plausible and achievable Fully Homomorphic Encryption (FHE)
scheme, which allows any computable function to perform on the encrypted data,
was introduced by Craig Gentry in 2009. Even though this was a major
achievement, different implementations so far demonstrated that FHE still needs
to be improved significantly to be practical on every platform. First, we
present the basics of HE and the details of the well-known Partially
Homomorphic Encryption (PHE) and Somewhat Homomorphic Encryption (SWHE), which
are important pillars of achieving FHE. Then, the main FHE families, which have
become the base for the other follow-up FHE schemes are presented. Furthermore,
the implementations and recent improvements in Gentry-type FHE schemes are also
surveyed. Finally, further research directions are discussed. This survey is
intended to give a clear knowledge and foundation to researchers and
practitioners interested in knowing, applying, as well as extending the state
of the art HE, PHE, SWHE, and FHE systems.Comment: - Updated. (October 6, 2017) - This paper is an early draft of the
survey that is being submitted to ACM CSUR and has been uploaded to arXiv for
feedback from stakeholder
On Security and reliability using cooperative transmissions in sensor networks
Cooperative transmissions have received recent attention and research papers have demonstrated their benefits for wireless networks. Such benefits include improving the reliability of links through diversity and/or increasing the reach of a link compared to a single transmitter transmitting to a single receiver (single-input single-output or SISO). In one form of cooperative transmissions, multiple nodes can act as virtual antenna elements and provide diversity gain or range improvement using space-time coding. In a multi-hop ad hoc or sensor network, a source node can make use of its neighbors as relays with itself to reach an intermediate node with greater reliability or at a larger distance than otherwise possible. The intermediate node will use its neighbors in a similar manner and this process continues till the destination is reached. Thus, for the same reliability of a link as SISO, the number of hops between a source and destination may be reduced using cooperative transmissions as each hop spans a larger distance. However, the presence of ma-licious or compromised nodes in the network impacts the benefits obtained with cooperative transmissions. Using more relays can increase the reach of a link, but if one or more relays are malicious, the transmission may fail. However, the relationships between the number of relays, the number of hops, and success probabilities are not trivial to determine. In this paper, we analyze this problem to understand the conditions under which cooperative transmissions fare better or worse than SISO transmissions. We take into consideration additional parameters such as the path-loss exponent and provide a framework that allows us to evaluate the conditions when cooperative transmissions are better than SISO transmissions. This analysis provides insights that can be employed before resorting to simulations or experimentation. © Springer Science+Business Media, LLC 2012
The Marmara Sea Gateway since ~16Â ky BP: non-catastrophic causes of paleoceanographic events in the Black Sea at 8.4 and 7.15Â ky BP
The Late Quaternary history of connection of the Black Sea to the Eastern
Mediterranean has been intensely debated. Ryan, Pitman and coworkers
advocate two pulses of outflow from the Black Sea to the world ocean at
~16–14.7 ky BP and ~11–10 ky BP. From ~14.7–11 ky BP and from ~10–8.4
ky BP, they suggest that the level of the Black Sea fell to ~ -100 m. At 8.4 ky
BP, they further claim that a catastrophic flood occurred in a geological
instant, refilling the Black Sea with saline waters from the Mediterranean. In
contrast, we continue to gather evidence from seismic profiles and dated cores
in the Marmara Sea which demonstrate conclusively that the proposed flood
did not occur. Instead, the Black Sea has been at or above the Bosphorus sill
depth and flowing into the world ocean unabated since ~10.5 ky BP. This
conclusion is based on continuous Holocene water-column stratification
(leading to sapropel deposition in the Marmara Sea and the Aegean Sea),
proxy indicators of sea-surface salinity, and migration of endemic species
across the Bosphorus in both directions whenever appropriate hydrographic
conditions existed in the strait. The two pulses of outflow documented by
Ryan, Pitman and coworkers find support in our data, and we have modified our earlier interpretations so that these pulses now coincide with the
development of mid-shelf deltas: \Delta 2 (16–14.7 ky BP) and \Delta 1 (10.5–9 ky BP)
at the southern end of the Bosphorus Strait. However, continued Black Sea
outflow after 9 ky BP prevented the northward advection of Mediterranean
water and the entry of open-marine species into the Black Sea for more than
1000 years. Sufficient Mediterranean water to change the Sr-isotopic
composition of slope and shelf water masses was not available until ~8.4 ky
BP (along with the first arrival of many varieties of marine fauna and flora),
whereas euryhaline molluscs did not successfully populate the Black Sea
shelves until ~7.15 ky BP. Instead of relying on catastrophic events, we
recognize a slow, progressive reconnection of the Black Sea to the world
ocean, accompanied by significant time lags
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