How Risky Is the Random-Oracle Model?
- Gaëtan LeurentAffiliated withDGA and ENS
- , Phong Q. NguyenAffiliated withINRIA and ENS
RSA-FDH and many other schemes secure in the Random-Oracle Model (ROM) require a hash function with output size larger than standard sizes. We show that the random-oracle instantiations proposed in the literature for such cases are weaker than a random oracle, including the proposals by Bellare and Rogaway from 1993 and 1996, and the ones implicit in IEEE P1363 and PKCS standards: for instance, we obtain a 267 preimage attack on BR93 for 1024-bit digests. Next, we study the security impact of hash function defects for ROM signatures. As an extreme case, we note that any hash collision would suffice to disclose the master key in the ID-based cryptosystem by Boneh et al. from FOCS ’07, and the secret key in the Rabin-Williams signature for which Bernstein proved tight security at EUROCRYPT ’08. Interestingly, for both of these schemes, a slight modification can prevent these attacks, while preserving the ROM security result. We give evidence that in the case of RSA and Rabin/Rabin-Williams, an appropriate PSS padding is more robust than all other paddings known.
- How Risky Is the Random-Oracle Model?
- Book Title
- Advances in Cryptology - CRYPTO 2009
- Book Subtitle
- 29th Annual International Cryptology Conference, Santa Barbara, CA, USA, August 16-20, 2009. Proceedings
- pp 445-464
- Print ISBN
- Online ISBN
- Series Title
- Lecture Notes in Computer Science
- Series Volume
- Series ISSN
- Springer Berlin Heidelberg
- Copyright Holder
- Springer-Verlag Berlin Heidelberg
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