## CryptoDB

### Paper: A Fast and Key-Efficient Reduction of Chosen- Ciphertext to Known-Plaintext Security

Authors: Ueli Maurer Johan Sjödin URL: http://eprint.iacr.org/2006/071 Search ePrint Search Google Motivated by the quest for reducing assumptions in security proofs in cryptography, this paper is concerned with designing efficient symmetric encryption and authentication schemes based on any weak pseudorandom function (PRF) which can be much more efficiently implemented than PRFs. Damgard and Nielsen (CRYPTO '02) have shown how to construct an efficient symmetric encryption scheme based on any weak PRF that is provably secure against chosen-plaintext attacks. The main ingredient is a range-extension construction for weak PRFs. By using well-known techniques, they also showed how their scheme can be made secure against the stronger chosen-ciphertext attacks. The results of our paper are three-fold. First, we give a range-extension construction for weak PRFs that is optimal within a large and natural class of reductions (especially all known today). Second, we propose a construction of a regular PRF from any weak PRF. Third, these two results imply a (for long messages) much more efficient chosen-ciphertext secure encryption scheme than the one proposed by Damgard and Nielsen. The results also give answers to open questions posed by Naor and Reingold (CRYPTO '98) and by Damgard and Nielsen.
##### BibTeX
@misc{eprint-2006-21564,
title={A Fast and Key-Efficient Reduction of Chosen- Ciphertext to Known-Plaintext Security},
booktitle={IACR Eprint archive},
keywords={Weak Pseudo-Random Function, Known-Plaintext Attack, Chosen-Ciphertext Attack, Symmetric Encryption},
url={http://eprint.iacr.org/2006/071},
note={ jsjoedin@gmail.com 13717 received 24 Feb 2006, last revised 23 Jul 2007},
author={Ueli Maurer and Johan Sjödin},
year=2006
}