OAEP reconsidered

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

The OAEP encryption scheme was introduced by Bellare and Rogaway at Eurocrypt '94. It converts any trapdoor permutation scheme into a public-key encryption scheme. OAEP is widely believed to provide resistance against adaptive chosen ciphertext attack. The main justification for this belief is a supposed proof of security in the random oracle model, assuming the underlying trapdoor permutation scheme is one way. This paper shows conclusively that this justification is invalid. First, it observes that there appears to be a non-trivial gap in the OAEP security proof. Second, it proves that this gap cannot be filled, in the sense that there can be no standard "black box" security reduction for OAEP. This is done by proving that there exists an oracle relative to which the general OAEP scheme is insecure. The paper also presents a new scheme OAEP+, along with a complete proof of security in the random oracle model. OAEP+ is essentially just as efficient as OAEP, and even has a tighter security reduction. It should be stressed that these results do not imply that a particular instantiation of OAEP, such as RSA-OAEP, is insecure. They simply undermine the original justification for its security. In fact, it turns out- essentially by accident, rather than by design-that RSA-OAEP is secure in the random oracle model; however, this fact relies on special algebraic properties of the RSA function, and not on the security of the general OAEP scheme.

Original languageEnglish (US)
Title of host publicationAdvances in Cryptology, CRYPTO 2001 - 21st Annual International Cryptology Conference, Proceedings
EditorsJoe Kilian
PublisherSpringer Verlag
Pages239-259
Number of pages21
ISBN (Print)3540424563, 9783540424567
DOIs
StatePublished - 2001
Event21st Annual International Cryptology Conference, CRYPTO 2001 - Santa Barbara, CA, United States
Duration: Aug 19 2001Aug 23 2001

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume2139 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349

Other

Other21st Annual International Cryptology Conference, CRYPTO 2001
CountryUnited States
CitySanta Barbara, CA
Period8/19/018/23/01

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Computer Science(all)

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  • Cite this

    Shoup, V. (2001). OAEP reconsidered. In J. Kilian (Ed.), Advances in Cryptology, CRYPTO 2001 - 21st Annual International Cryptology Conference, Proceedings (pp. 239-259). (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); Vol. 2139 LNCS). Springer Verlag. https://doi.org/10.1007/3-540-44647-8_15