Paper 2003/255

Improved Constructions for Universal Re-encryption.

Peter Fairbrother

Abstract

Golle et al introduced universal re-encryption, defining it as re- encryption by a player who does not know the key used for the original encryption, but which still allows an intended player to recover the plaintext. Universal re-encryption is potentially useful as part of many information-hiding techniques, as it allows any player to make ciphertext unidentifiable without knowing the key used. Golle et al’s techniques for universal re-encryption are reviewed, and improved constructions for both simple and hybrid universal re-encryption systems are presented, including a hybrid construction that permits indefinite re-encryptions with better efficiency and an almost-optimally small increase in file size. Some implementational issues and possible future directions are also discussed.

Note: Tidied up, new section on semantic security