Cryptology ePrint Archive: Report 2007/168

Random Oracles and Auxiliary Input

Dominique Unruh

Abstract: We introduce a variant of the random oracle model where oracle-dependent auxiliary input is allowed. In this setting, the adversary gets an auxiliary input that can contain information about the random oracle. Using simple examples we show that this model should be preferred over the classical variant where the auxiliary input is independent of the random oracle.

In the presence of oracle-dependent auxiliary input, the most important proof technique in the random oracle model - lazy sampling - does not apply directly. We present a theorem and a variant of the lazy sampling technique that allows one to perform proofs in the new model almost as easily as in the old one. As an application of our approach and to illustrate how existing proofs can be adapted, we prove that RSA-OAEP is IND-CCA2 secure in the random oracle model with oracle-dependent auxiliary input.

Category / Keywords: foundations / Random oracles, auxiliary input, proof techniques

Publication Info: This is the full version of a paper appearing at Crypto 2007

Date: received 7 May 2007, last revised 8 Jun 2007

Contact author: unruh at cs uni-sb de

Available format(s): PDF | BibTeX Citation

Note: Minor corrections due to referee comments.

Version: 20070608:161937 (All versions of this report)

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