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Abstract in English

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Fabrice Mouhartem 2018-06-19 13:22:06 +02:00
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\addcontentsline{toc}{chapter}{Abstract} \addcontentsline{toc}{chapter}{Abstract}
\addcontentsline{tof}{chapter}{Résumé en anglais} \addcontentsline{tof}{chapter}{Résumé en anglais}
\vspace{1.5cm}
In this thesis, we study provably secure privacy-preserving cryptographic constructions.
We focus on zero-knowledge proofs and their applications.
Group signatures are an example of such constructions.
This primitive allows users to sign messages on behalf of a group (which they formerly join), while staying anonymous inside this group.
Additionally, users remains accountable for their behavior as another independent authority, a judge, is empowered with a secret information to lift anonymity of given signatures.
This construction has applications in anonymous access control, such as public transportations.
Whenever someone enters a public transport, he signs a timestamp. Doing this proves that he belongs to the group of people with a valid subscription.
In case of problem, the transportation company hands the record of suspicious signatures to the police, which is able to un-anonymize them.
We propose two constructions for dynamically growing group signatures. The first is based on pairings assumptions and aims practicality, while the second one is proven secure under lattice assumptions for the sake of not putting all eggs in the same basket.
Following the same spirit, we also propose two constructions for privacy-preserving cryptography.
The first one is a group encryption scheme, which is the encryption analogue of group signatures. Here, the goal is to hide the recipient of a message who belongs to a group, while proving some properties on the message, like the absence of malwares.
The second is an adaptive oblivious transfer scheme, which allows a user to anonymously query an encrypted database, while keeping the unrequested messages hidden.
These constructions were made possible through a series of work improving the expressiveness of Stern-like zero-knowledge arguments.