Cryptology ePrint Archive: Report 2007/235

Blind Identity-Based Encryption and Simulatable Oblivious Transfer

Matthew Green and Susan Hohenberger

Abstract: In an identity-based encryption (IBE) scheme, there is a {\em key extraction} protocol where a user submits an identity string to a master authority who then returns the corresponding secret key for that identity. In this work, we describe how this protocol can be performed efficiently and in a {\em blind} fashion for several known IBE schemes; that is, a user can obtain a secret key for an identity without the master authority learning anything about this identity.

We formalize this notion as {\em blind IBE} and discuss the many practical applications of such a scheme. In particular, we build upon the recent work of Camenisch, Neven, and shelat in Eurocrypt 2007 to construct oblivious transfer (OT) schemes which achieve full simulatability for both sender and receiver. OT constructions with comparable efficiency prior to Camenisch et al.\ were proven secure in the weaker half-simulation model. Our OT schemes can be constructed generically from any blind IBE, and thus require only static complexity assumptions (e.g., DBDH) whereas prior comparable schemes require dynamic complexity assumptions (e.g., $q$-PDDH).

Category / Keywords: cryptographic protocols / identity-based encryption, oblivious transfer, blind key extraction

Date: received 14 Jun 2007, last revised 2 May 2008

Contact author: mgreen at cs jhu edu

Available format(s): PDF | BibTeX Citation

Note: An extended abstract of this paper appeared in ASIACRYPT 2007. This is the full version.

Version: 20080502:155616 (All versions of this report)

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