Cryptology ePrint Archive: Report 2006/223

What Hashes Make RSA-OAEP Secure?

Daniel R. L. Brown

Abstract: Firstly, we demonstrate a pathological hash function choice that makes RSA-OAEP insecure. This shows that at least some security property is necessary for the hash functions used in RSA-OAEP. Nevertheless, we conjecture that only some very minimal security properties of the hash functions are actually necessary for the security of RSA-OAEP. Secondly, we consider certain types of reductions that could be used to prove the OW-CPA (i.e., the bare minimum) security of RSA-OAEP. We apply metareductions that show if such reductions existed, then RSA-OAEP would be OW-CCA2 insecure, or even worse, that the RSA problem would solvable. Therefore, it seems unlikely that such reductions could exist. Indeed, no such reductions proving the OW-CCA2 security of RSA-OAEP exist.

Category / Keywords: public-key cryptography / RSA, OAEP, Provable Security, Public-key Encryption, IND-CCA2, OW-CPA, Impossibiltiy Results

Date: received 30 Jun 2006, last revised 8 Aug 2007

Contact author: dbrown at certicom com

Available format(s): PDF | BibTeX Citation

Note: Re-written for better clarity in response to various comments.

Version: 20070808:185853 (All versions of this report)

Short URL: ia.cr/2006/223