535 research outputs found
Spoiled Onions: Exposing Malicious Tor Exit Relays
Several hundred Tor exit relays together push more than 1 GiB/s of network
traffic. However, it is easy for exit relays to snoop and tamper with
anonymised network traffic and as all relays are run by independent volunteers,
not all of them are innocuous.
In this paper, we seek to expose malicious exit relays and document their
actions. First, we monitored the Tor network after developing a fast and
modular exit relay scanner. We implemented several scanning modules for
detecting common attacks and used them to probe all exit relays over a period
of four months. We discovered numerous malicious exit relays engaging in
different attacks. To reduce the attack surface users are exposed to, we
further discuss the design and implementation of a browser extension patch
which fetches and compares suspicious X.509 certificates over independent Tor
circuits.
Our work makes it possible to continuously monitor Tor exit relays. We are
able to detect and thwart many man-in-the-middle attacks which makes the
network safer for its users. All our code is available under a free license
UHE neutrino and cosmic ray emission from GRBs: revising the models and clarifying the cosmic ray-neutrino connection
Gamma-ray bursts (GRBs) have long been held as one of the most promising
sources of ultra-high energy (UHE) neutrinos. The internal shock model of GRB
emission posits the joint production of UHE cosmic ray (UHECRs, above 10^8
GeV), photons, and neutrinos, through photohadronic interactions between source
photons and magnetically-confined energetic protons, that occur when
relativistically-expanding matter shells loaded with baryons collide with one
another. While neutrino observations by IceCube have now ruled out the simplest
version of the internal shock model, we show that a revised calculation of the
emission, together with the consideration of the full photohadronic cross
section and other particle physics effects, results in a prediction of the
prompt GRB neutrino flux that still lies one order of magnitude below the
current upper bounds, as recently exemplified by the results from ANTARES. In
addition, we show that by allowing protons to directly escape their magnetic
confinement without interacting at the source, we are able to partially
decouple the cosmic ray and prompt neutrino emission, which grants the freedom
to fit the UHECR observations while respecting the neutrino upper bounds.
Finally, we briefly present advances towards pinning down the precise relation
between UHECRs and UHE neutrinos, including the baryonic loading required to
fit UHECR observations, and we will assess the role that very large volume
neutrino telescopes play in this.Comment: 4 pages, 2 figures. To be published in Proceedings of the 6th Very
Large Volume Neutrino Telescope Workshop (VLVnT13), Stockholm, Sweden, 5-7
August, 201
Magnetic Field and Flavor Effects on the Gamma-Ray Burst Neutrino Flux
We reanalyze the prompt muon neutrino flux from gamma-ray bursts (GRBs), at
the example of the often used reference Waxman-Bahcall GRB flux, in terms of
the particle physics involved. We first reproduce this reference flux treating
synchrotron energy losses of the secondary pions explicitly. Then we include
additional neutrino production modes, the neutrinos from muon decays, the
magnetic field effects on all secondary species, and flavor mixing with the
current parameter uncertainties. We demonstrate that the combination of these
effects modifies the shape of the original Waxman-Bahcall GRB flux
significantly, and changes the normalization by a factor of three to four. As a
consequence, the gamma-ray burst search strategy of neutrino telescopes may be
based on the wrong flux shape, and the constraints derived for the GRB neutrino
flux, such as the baryonic loading, may in fact be already much stronger than
anticipated.Comment: 4 pages, 3 figures. Minor clarifications. Final version to appear in
Phys. Rev.
Are gamma-ray bursts the sources of ultra-high energy cosmic rays?
We reconsider the possibility that gamma-ray bursts (GRBs) are the sources of
the ultra-high energy cosmic rays (UHECRs) within the internal shock model,
assuming a pure proton composition of the UHECRs. For the first time, we
combine the information from gamma-rays, cosmic rays, prompt neutrinos, and
cosmogenic neutrinos quantitatively in a joint cosmic ray production and
propagation model, and we show that the information on the cosmic energy budget
can be obtained as a consequence. In addition to the neutron model, we consider
alternative scenarios for the cosmic ray escape from the GRBs, i.e., that
cosmic rays can leak from the sources. We find that the dip model, which
describes the ankle in UHECR observations by the pair production dip, is
strongly disfavored in combination with the internal shock model because a)
unrealistically high baryonic loadings (energy in protons versus energy in
electrons/gamma-rays) are needed for the individual GRBs and b) the prompt
neutrino flux easily overshoots the corresponding neutrino bound. On the other
hand, GRBs may account for the UHECRs in the ankle transition model if cosmic
rays leak out from the source at the highest energies. In that case, we
demonstrate that future neutrino observations can efficiently test most of the
parameter space -- unless the baryonic loading is much larger than previously
anticipated.Comment: 55 pages, 23 figures, 1 table. Version accepted for publication in
Astroparticle Physics. Main analysis performed with TA data; for plots with
HiRes data, see v
Neutrino and cosmic-ray emission from multiple internal shocks in gamma-ray bursts
Gamma-ray bursts are short-lived, luminous explosions at cosmological
distances, thought to originate from relativistic jets launched at the deaths
of massive stars. They are among the prime candidates to produce the observed
cosmic rays at the highest energies. Recent neutrino data have, however,
started to constrain this possibility in the simplest models with only one
emission zone. In the classical theory of gamma-ray bursts, it is expected that
particles are accelerated at mildly relativistic shocks generated by the
collisions of material ejected from a central engine. We consider neutrino and
cosmic-ray emission from multiple emission regions since these internal
collisions must occur at very different radii, from below the photosphere all
the way out to the circumburst medium, as a consequence of the efficient
dissipation of kinetic energy. We demonstrate that the different messengers
originate from different collision radii, which means that multi-messenger
observations open windows for revealing the evolving GRB outflows.Comment: 12 pages, 7 figures. Matches published versio
How to Bootstrap Anonymous Communication
We ask whether it is possible to anonymously communicate a large amount of
data using only public (non-anonymous) communication together with a small
anonymous channel. We think this is a central question in the theory of
anonymous communication and to the best of our knowledge this is the first
formal study in this direction. To solve this problem, we introduce the concept
of anonymous steganography: think of a leaker Lea who wants to leak a large
document to Joe the journalist. Using anonymous steganography Lea can embed
this document in innocent looking communication on some popular website (such
as cat videos on YouTube or funny memes on 9GAG). Then Lea provides Joe with a
short key which, when applied to the entire website, recovers the document
while hiding the identity of Lea among the large number of users of the
website. Our contributions include:
- Introducing and formally defining anonymous steganography,
- A construction showing that anonymous steganography is possible (which uses
recent results in circuits obfuscation),
- A lower bound on the number of bits which are needed to bootstrap anonymous
communication.Comment: 15 page
- …