Date Added: Sep 2010
Exposure of a secret key is a significant threat in practice. As a notion of security against key exposure, Dodis et al. advocated key-insulated security, and proposed concrete Key-Insulated Encryption (KIE) schemes in which secret keys are periodically updated by using a physically "Insulated" helper key. For significantly reducing possibility of exposure of the helper key, Hanaoka et al. further proposed the notion of Parallel KIE (PKIE) in which multiple helper keys are used in alternate shifts. They also pointed out that in contrast to the case of the standard KIE, PKIE cannot be straightforwardly obtained from Identity-Based Encryption (IBE).