Cryptology ePrint Archive: Report 2000/061

RSA-OAEP is Secure under the RSA Assumption

Eiichiro Fujisaki and Tatsuaki Okamoto and David Pointcheval and Jacques Stern

Abstract: Recently Victor Shoup noted that there is a gap in the widely-believed security result of OAEP against adaptive chosen-ciphertext attacks. Moreover, he showed that, presumably, OAEP cannot be proven secure from the {\it one-wayness} of the underlying trapdoor permutation. This paper establishes another result on the security of OAEP. It proves that OAEP offers semantic security against adaptive chosen-ciphertext attacks, in the random oracle model, under the {\it partial-domain} one-wayness of the underlying permutation. Therefore, this uses a formally stronger assumption. Nevertheless, since partial-domain one-wayness of the RSA function is equivalent to its (full-domain) one-wayness, it follows that the security of RSA--OAEP can actually be proven under the sole RSA assumption, although the reduction is not tight.

Category / Keywords: cryptographic protocols /

Date: received 27 Nov 2000, last revised 29 May 2001

Contact author: David Pointcheval at ens fr

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Version: 20010831:070009 (All versions of this report)

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