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Delegation in functional encryption

Abstract : Functional encryption is a recent paradigm that generalizes the classical public key encryption. This formalization aims to finely manage both the access control to the encrypted data, and the information revealed by the decryption. This thesis studies possibilities of delegation through these two sides. First, we deal with a multi-client context : several users provide each one an encryption of personal data, and an entity wishes to extract information from the aggregate of those inputs. Our contribution in this environment consists to provide these clients the possibility to give, or refuse, their consent for such an extraction. To this aim, we describe constructions of multi-client functional encryption. We then formalize several levels of security and provide methods to reach them. Eventually, we decentralize the construction of the functional decryption key, so that one needs the agreement of all clients to get a functional decryption key. All this, in a practical way. Second, we consider a more specific case where a video content provider wishes to delegate the distribution of his creation, but without revealing it. Our solution is a key encapsulation mechanism, derived from attribute-based encryption, with a particular property. The provider uses it to encapsulate the key of the encrypted stream under several attributes, and provides the encapsulations to the distributor. This "content manager" can then use the property to combine the encapsulations and make a new one under the access policy of his choice.
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Contributor : Jeremy Chotard <>
Submitted on : Thursday, December 5, 2019 - 3:17:53 PM
Last modification on : Thursday, February 13, 2020 - 5:08:07 PM
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  • HAL Id : tel-02394349, version 1



Jérémy Chotard. Delegation in functional encryption. Cryptography and Security [cs.CR]. Université de Limoges, 2019. English. ⟨NNT : 2019LIMO0088⟩. ⟨tel-02394349⟩



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