91,122 research outputs found
Message Complexity of Population Protocols
The standard population protocol model assumes that when two agents interact,
each observes the entire state of the other agent. We initiate the study of
for population protocols, where the state of an
agent is divided into an externally-visible and an internal
component, where only the message can be observed by the other agent in an
interaction.
We consider the case of message complexity. When time is unrestricted,
we obtain an exact characterization of the stably computable predicates based
on the number of internal states : If then the protocol
computes semilinear predicates (unlike the original model, which can compute
non-semilinear predicates with ), and otherwise it computes a
predicate decidable by a nondeterministic -space-bounded Turing
machine. We then introduce novel expected time
protocols for junta/leader election and general purpose broadcast correct with
high probability, and approximate and exact population size counting correct
with probability 1. Finally, we show that the main constraint on the power of
bounded-message-size protocols is the size of the internal states: with
unbounded internal states, any computable function can be computed with
probability 1 in the limit by a protocol that uses only
messages
Passively Mobile Communicating Logarithmic Space Machines
We propose a new theoretical model for passively mobile Wireless Sensor
Networks. We call it the PALOMA model, standing for PAssively mobile
LOgarithmic space MAchines. The main modification w.r.t. the Population
Protocol model is that agents now, instead of being automata, are Turing
Machines whose memory is logarithmic in the population size n. Note that the
new model is still easily implementable with current technology. We focus on
complete communication graphs. We define the complexity class PLM, consisting
of all symmetric predicates on input assignments that are stably computable by
the PALOMA model. We assume that the agents are initially identical.
Surprisingly, it turns out that the PALOMA model can assign unique consecutive
ids to the agents and inform them of the population size! This allows us to
give a direct simulation of a Deterministic Turing Machine of O(nlogn) space,
thus, establishing that any symmetric predicate in SPACE(nlogn) also belongs to
PLM. We next prove that the PALOMA model can simulate the Community Protocol
model, thus, improving the previous lower bound to all symmetric predicates in
NSPACE(nlogn). Going one step further, we generalize the simulation of the
deterministic TM to prove that the PALOMA model can simulate a Nondeterministic
TM of O(nlogn) space. Although providing the same lower bound, the important
remark here is that the bound is now obtained in a direct manner, in the sense
that it does not depend on the simulation of a TM by a Pointer Machine.
Finally, by showing that a Nondeterministic TM of O(nlogn) space decides any
language stably computable by the PALOMA model, we end up with an exact
characterization for PLM: it is precisely the class of all symmetric predicates
in NSPACE(nlogn).Comment: 22 page
Scalable Byzantine Reliable Broadcast
Byzantine reliable broadcast is a powerful primitive that allows a set of processes to agree on a message from a designated sender, even if some processes (including the sender) are Byzantine. Existing broadcast protocols for this setting scale poorly, as they typically build on quorum systems with strong intersection guarantees, which results in linear per-process communication and computation complexity.
We generalize the Byzantine reliable broadcast abstraction to the probabilistic setting, allowing each of its properties to be violated with a fixed, arbitrarily small probability. We leverage these relaxed guarantees in a protocol where we replace quorums with stochastic samples. Compared to quorums, samples are significantly smaller in size, leading to a more scalable design. We obtain the first Byzantine reliable broadcast protocol with logarithmic per-process communication and computation complexity.
We conduct a complete and thorough analysis of our protocol, deriving bounds on the probability of each of its properties being compromised. During our analysis, we introduce a novel general technique that we call adversary decorators. Adversary decorators allow us to make claims about the optimal strategy of the Byzantine adversary without imposing any additional assumptions. We also introduce Threshold Contagion, a model of message propagation through a system with Byzantine processes. To the best of our knowledge, this is the first formal analysis of a probabilistic broadcast protocol in the Byzantine fault model. We show numerically that practically negligible failure probabilities can be achieved with realistic security parameters
Pseudo-random Aloha for Enhanced Collision-recovery in RFID
In this letter we motivate the need to revisit the MAC protocol used in Gen2
RFID system in order to leverage receiver structures with Collision Recovery
capabilities at the PHY layer. To this end we propose to consider a simple
variant of the Framed Slotted Aloha with pseudo-random (deterministic) slot
selection as opposite to the classical random selection. Pseudo-random access
allows naturally to implement Inter-frame Successive Interference Cancellation
(ISIC) without changing the PHY modulation and coding format of legacy RFID
standard. By means of simulations we show that ISIC can bring 20-25% gain in
throughput with respect to traditional intra-frame SIC. Besides that, we
elaborate on the potential of leveraging pseudo-random access protocols in
combination with advanced PHY techniques in the context of RFID applications.Comment: This manuscript has been submitted to IEEE on the 19th September 201
PADS: Practical Attestation for Highly Dynamic Swarm Topologies
Remote attestation protocols are widely used to detect device configuration
(e.g., software and/or data) compromise in Internet of Things (IoT) scenarios.
Unfortunately, the performances of such protocols are unsatisfactory when
dealing with thousands of smart devices. Recently, researchers are focusing on
addressing this limitation. The approach is to run attestation in a collective
way, with the goal of reducing computation and communication. Despite these
advances, current solutions for attestation are still unsatisfactory because of
their complex management and strict assumptions concerning the topology (e.g.,
being time invariant or maintaining a fixed topology). In this paper, we
propose PADS, a secure, efficient, and practical protocol for attesting
potentially large networks of smart devices with unstructured or dynamic
topologies. PADS builds upon the recent concept of non-interactive attestation,
by reducing the collective attestation problem into a minimum consensus one. We
compare PADS with a state-of-the art collective attestation protocol and
validate it by using realistic simulations that show practicality and
efficiency. The results confirm the suitability of PADS for low-end devices,
and highly unstructured networks.Comment: Submitted to ESORICS 201
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