169 research outputs found
Keep the Dirt: Tainted TreeKEM, Adaptively and Actively Secure Continuous Group Key Agreement
While messaging systems with strong security guarantees are widely used in practice, designing a protocol that scales efficiently to large groups and enjoys similar security guarantees remains largely open. The two existing proposals to date are ART (Cohn-Gordon et al., CCS18) and TreeKEM (IETF, The Messaging Layer Security Protocol, draft). TreeKEM is the currently considered candidate by the IETF MLS working group, but dynamic group operations (i.e. adding and removing users) can cause efficiency issues. In this paper we formalize and analyze a variant of TreeKEM which we term Tainted TreeKEM (TTKEM for short). The basic idea underlying TTKEM was suggested by Millican (MLS mailing list, February 2018). This version is more efficient than TreeKEM for some natural distributions of group operations, we quantify this through simulations.
Our second contribution is two security proofs for TTKEM which establish post compromise and forward secrecy even against adaptive attackers. If is the group size and the number of operations, the security loss (to the underlying PKE) in the Random Oracle Model is a polynomial factor , and in the Standard Model a quasipolynomial . Our proofs can be adapted to TreeKEM as well. Before our work no security proof for any TreeKEM-like protocol establishing tight security against an adversary who can adaptively choose the sequence of operations was known. We also are the first to prove (or even formalize) active security where the server can arbitrarily deviate from the protocol specification. Proving fully active security - where also the users can arbitrarily deviate - remains open
Fast Growth of Supermassive Black Holes in Galaxies
We report on a calculation of the growth of the mass of supermassive black
holes at galactic centers from dark matter and Eddington - limited baryonic
accretion. Assuming that dark matter halos are made of fermions and harbor
compact degenerate Fermi balls of masses from to
, we find that dark matter accretion can boost the mass of
seed black holes from about to black
holes, which then grow by Eddington - limited baryonic accretion to
supermassive black holes of . We then show that the
formation of the recently detected supermassive black hole of at a redshift of in the quasar SDSS
J114816.64+525150.3 could be understood if the black hole completely consumes
the degenerate Fermi ball and then grows by Eddington - limited baryonic
accretion. In the context of this model we constrain the dark matter particle
masses to be within the range from 12 to about 450 . Finally we investigate the black hole growth dependence on the
formation time of the seed BH and on the mass of the seed BH. We find that in
order to fit the observed data point of
and , dark matter accretion cannot start later than about years and the seed BH cannot be greater than about
. Our results are in full agreement with the WMAP observations
that indicate that the first onset of star formation might have occurred at a
redshift of . For other models of dark matter particle masses,
corresponding constraints may be derived from the growth of black holes in the
center of galaxies.Comment: New black hole growth mechnism, references added, 13 pages, accepted
for publication in Astronomy & Astrophysics Journa
Brain oscillations and connectivity in autism spectrum disorders (ASD):new approaches to methodology, measurement and modelling
Although atypical social behaviour remains a key characterisation of ASD, the presence ofsensory and perceptual abnormalities has been given a more central role in recentclassification changes. An understanding of the origins of such aberrations could thus prove afruitful focus for ASD research. Early neurocognitive models of ASD suggested that thestudy of high frequency activity in the brain as a measure of cortical connectivity mightprovide the key to understanding the neural correlates of sensory and perceptual deviations inASD. As our review shows, the findings from subsequent research have been inconsistent,with a lack of agreement about the nature of any high frequency disturbances in ASD brains.Based on the application of new techniques using more sophisticated measures of brainsynchronisation, direction of information flow, and invoking the coupling between high andlow frequency bands, we propose a framework which could reconcile apparently conflictingfindings in this area and would be consistent both with emerging neurocognitive models ofautism and with the heterogeneity of the condition
Pelvic trauma : WSES classification and guidelines
Complex pelvic injuries are among the most dangerous and deadly trauma related lesions. Different classification systems exist, some are based on the mechanism of injury, some on anatomic patterns and some are focusing on the resulting instability requiring operative fixation. The optimal treatment strategy, however, should keep into consideration the hemodynamic status, the anatomic impairment of pelvic ring function and the associated injuries. The management of pelvic trauma patients aims definitively to restore the homeostasis and the normal physiopathology associated to the mechanical stability of the pelvic ring. Thus the management of pelvic trauma must be multidisciplinary and should be ultimately based on the physiology of the patient and the anatomy of the injury. This paper presents the World Society of Emergency Surgery (WSES) classification of pelvic trauma and the management Guidelines.Peer reviewe
Jacques Roux avant la Révolution
Markov Walter. Jacques Roux avant la Révolution . In: Annales historiques de la Révolution française, n°174, 1963. pp. 453-470
Le placard de Jacques Roux contre Epellet
Markov Walter. Le placard de Jacques Roux contre Epellet . In: Annales historiques de la Révolution française, n°180, 1965. pp. 204-210
J. H. Campe. Lettres de Paris, 1961
Markov Walter. J. H. Campe. Lettres de Paris, 1961. In: Annales historiques de la Révolution française, n°175, 1964. pp. 120-121
Jacques M. Zacker. Le Mouvement des «Enragés», 1961
Markov Walter. Jacques M. Zacker. Le Mouvement des «Enragés», 1961. In: Annales historiques de la Révolution française, n°176, 1964. pp. 228-230
Julie Mochekovskaïa. Georg Forster : philosophe et révolutionnaire allemand du XVIIIe siècle, 1961
Markov Walter. Julie Mochekovskaïa. Georg Forster : philosophe et révolutionnaire allemand du XVIIIe siècle, 1961. In: Annales historiques de la Révolution française, n°193, 1968. pp. 408-409
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