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cosec >students >Teaching >Winter 2007/2008 

Identity Based Encryption - Security Notions and New IBE Schemes for Sakai-Kasahara's Key Construction

Deniz Sarier (cosec, b-it)

Thursday, 08 November, 2007, 1500 sharp (s.t), b-it 1.25 (cosec meeting room)

In this master thesis, the security notions of Identity Based Encryption (IBE) are investigated including the setting for the multi-receiver case, where example schemes that are secure in the sense of indistinguishability are analysed. Additionally, two new proofs for the security of Sakai-Kasahara's IBE scheme (SK-IBE) are described, both of which do not require any reduction to intermediate schemes resulting in a more readable and direct proof.

The first proof requires a new generic construction for a key encapsulation mechanism (KEM) and a new assumption called Generalized $k-BCAA1'$, which is not stronger than the k-DHI assumption and is used as the underlying computational assumption of the GAP problem that the security proof is based on. The proof is described for selective and full identity attack models and its tightness is compared to the old proof. In addition, another generic model for a KEM is constructed and applied to SK-IBE. This way, the second proof for SK-IBE is based on the difficulty of the GAP k-BDHI problem, where k-BDHI assumption is a standard computational assumption. Again, the tightness of the reduction of the new proof is computed and compared to the old proof for the full identity attack model. (talk)

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