The self-sovereign identity (SSI) model entails the full responsibility and sovereignty of a user regarding his identity data. This identity data can contain private data which is solely known to the user. The user himself is therefore required to manage the whole lifecycle of his private data, including the backup and restore. We show that prior work on how to backup and restore the user's identity data does not meet the requirements of the SSI setting, and we present the first solution which does meet the requirements. Authenticated backup with auditing by remote entities (AWARE) combines SSI sustaining aspects and extends them to create a truly self-sovereign backup-and-restore protocol. In AWARE, trusted, physically met humans, called custodians, hold a secure device. Custodians with a secure device offer an offline backup possibility and a secure channel. The backup and restore are audited by commits on a publicly accessible distributed ledger. These commits are answered by auditing services which are required during restore. Only some auditing services hold relevant data for a restore. The self sovereignty of the user lies in the exclusive information which auditing services hold relevant data. AWARE is the first backup-and-restore mechanism that fully complies with the SSI model. We perform an indepth security-risk analysis of AWARE, showing a risk rating which is comparable to the best risk rating o related non-SSI-compliant backupand-restore mechanisms. We instantiate the AWARE protocol with cryptographic primitives providing a high security level of 256-bit. We show its implementation feasibility by providing a simulation of AWARE, and conclude with an estimated performance analysis on a microcontoller architecture based on our simulation and implementation results in the literature.

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The objective of this paper is to provide physical insights into the response of a turret-moored tanker in a severe sea state as a function of spectral wave characteristics. For one sea state various realizations of the wave process are applied to investigate the effect on maximum turret and anchor chain forces. Use is made of a validated mathematical model that accounts for the high and low-frequency dynamics of coupled tanker and anchor chains. Its predictions are compared with a simpler method and conclusions are drawn with respect to the significance of peak wave period, spectrum type, and chain damping.

Rapid developments in the field of synthetic fibres have lead to serious alternatives for the traditional catenary mooring systems in several applications. The use of synthetic fibres in mooring systems has received increasing attention, especially for deeper water. However a design based on these fibres requires modification in the analysis methods. Here the feasibility of mooring systems using a synthetic rope (with Dyneema®) compared to a wire rope is analyzed, for a water depth of 800 m. Differences between the systems are elucidated by showing results of a time domain analysis on a turret moored tanker. Different optimization criteria are considered. Generally speaking optimum moorings systems based on synthetic rope are stiffer and impose 10wer vertical turret loads than a wire rope mooring at increasing water depth. In return for the smaller tanker excursions, the vertical forces at the seabed are considerable for a synthetic mooring. INTRODUCTION Floating production facilities are being used at increasing depths. In deep water conventional mooring systems, based on wire rope and chain, have serious drawbacks and alternative systems (synthetic ropes) become more feasible, see e.g. ref. [11. However the dynamic behaviour of a synthetic mooring system is different from a mooring with wire rope, because of the absence of a catenary and the time-dependent properties of synthetic materials. Thus a conventional design may result in a sub-optimum for a synthetic material. Dyneema is a High Performance Polyethylene (HPPE) fibre, with a tensile strength similar to steel on a diameter basis, see also [2]. Ropes made of Dyneema are well suited for use in the marine environment under dynamic conditions (see ref. [3] & [4]). On the basis of these successful applications this material has been selected for this study. A turret moored tanker is a dynamical system subject to excitation due to wind, waves and current, For the design of a mooring system excitation forces and dynamic responses in terms of loading and tanker motion are required. The excitation depends on the environment, the reaction forces are a combination of hydrodynamic forces and restoring characteristics of the mooring system, see ref. [5] for a general discussion. The excitation forces can be divided in three groups, namely: average load, wave frequency (typical period: 5-20 see) and low frequency. The low frequency excitation is a combination of mean wind, current and wave drift forces, with a typical period of 50-500 sec. The natural frequency of the mooring system is generally in the low frequency range. The wave frequency loads are from the first order wave forces on the tanker and the resulting tanker motions are directly transferred to the mooring system. The average loads are from the steady wind, current and mean wave drift forces. Here a 200 kDWT tanker has been moored in a water depth of 800 m, and the behaviour of the tanker plus mooring system is studied under survival conditions. Different optimization criteria are used to evaluate a synthetic mooring system.