Cryptology ePrint Archive: Report 2007/201

The BBG HIBE Has Limited Delegation

Hovav Shacham

Abstract: At Eurocrypt 2005, Boneh, Boyen, and Goh presented a hierarchical IBE for which they claimed a novel property, called limited delegation: it is possible to give an entity a private key that restricts it from generating descendant private keys beyond some depth d; in particular, with d equal to the entity's depth, such a key allows decryption only. In this paper, we argue that this claim is nonobvious and requires proof, provide a precise model for arguing about limited delegation, and prove that the Boneh-Boyen-Goh system does, in fact, have limited delegation. Whereas Boneh, Boyen, and Goh prove their system semantically secure under the BDHI assumption, our proof of limited delegation requires the stronger BDHE assumption.

Category / Keywords: public-key cryptography / identity-based encryption, limited delegation, BDHE

Date: received 29 May 2007

Contact author: hovav at cs stanford edu

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Version: 20070531:184510 (All versions of this report)

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