With the advent of Location-Based-Systems, positioning systems must face new security requirements: how to guarantee the authenticity of the geographical positon announced by a user before granting him access to location-restricted! resources. In this thesis, we are interested in the study of ! security ! protocols that can ensure autheniticity of the position announced by a user without the prior availability of any form of trusted architecture. A first result of our study is the proposal for a distance-bounding protocol based on asymmetric cryptography which allows a node knowing a public key to authenticate the holder of the associated private key, while establishing confidence in the distance between them. The distance measurement procedure is sufficently secure to resist to well-known attacks such as relay attacks, distance-, mafia- and terrorist-attacks. We then use such distance-bounding protocol to define an architecture for gathering privacy friendly location proofs. We define a location proof as a digital certificate attesting of presence of an individual at a location at a given time. The privacy properties we garanty through the use of our system are: the anonymity of users, un-linkability of their actions within the system and a strong binding between each user ! and the localization proof it is associated. on last property of our system is the possibility to use the same location proof to demonstrate different granularity of the associated position
