Decidability of Opacity with Non-Atomic Keys

Probabilistic Opacity for Markov Decision Processes

Opacity is a generic security property, that has been defined on (non probabilistic) transition systems and later on Markov chains with labels. For a secret predicate, given as a subset of runs, and a function describing the view of an external observer, the value of interest for opacity is a measure of the set of runs disclosing the secret. We extend this definition to the richer framework of ...

Decidability and Tameness in the Theory of Finite Semigroups

Is the soft excess in AGN real?

We systematically analyse all publicly available XMM-Newton spectra of radioquiet PG quasars. The soft X-ray excess in these objects is well modelled by an additional, cool, Compton scattering region. However, the remarkably constant temperature derived for this component over the whole sample requires a puzzling fine tuning of the parameters. Instead, we propose that the soft excess is an arti...

How to SYN in seven easy steps

This requires calculation of the opacity κλ; this is the core task of a spectral synthesis program. The opacity can be considered to consist of a continuous opacity, and opacity due to atomic line transitions. The main contribution to the continuous opacity is due to bound-free and free-free H transitions; other major sources (H+2 molecule, photoionisation of metals) also need to be considered....

Protocol Security Goals and the Size of Skeletons

We express security goals for a cryptographic protocol in a language of classical first order logic. Its semantics uses realized skeletons, which represent the regular (non-penetrator) parts of possible executions. Security goals are preserved under some homomorphisms between realized skeletons, yielding an appealing proof of the Comon-Lundh/Cortier theorem that two agents are sufficient for te...