Cycle‐walking revisited: consistency, security, and efficiency

Abstract

Cycle‐walking is a method that makes sure ciphertext falls in the acceptable range through encrypting plaintext repeatedly with some underlying cipher. This technology provides a general way to construct cryptographic schemes for various interesting applications, including enhancing existing system security without the change of original structure, encrypting multimedia data with the preservation of scalability, generating credit card numbers for Web transaction, and so on, which have a common feature that ciphertext is required to satisfy certain restrictions in order to allow some operations directly imposed on encrypted data. Nevertheless, as far as we know, there exists little work making rigorous analysis on cycle‐walking, especially its undeterministic efficiency, which may limit the application of schemes constructed by such technology or even lead it to unpracticality. In this paper, aiming at filling some gaps about cycle‐walking and helping cryptographic theory “catch up” with its application, we present the rigorous analysis on cycle‐walking's properties including consistency, security, and efficiency. On consistency, we show that cycle‐walking will necessarily arrive back with finite iteration rounds and its decryption reverses encryption. On security, we show that cycle‐walking would not degrade the security of underlying ciphers. On efficiency, instead of using “nondeterministic” to describe cycle‐walking's performance in previous work, we make precise analysis and provide the answer to “how long is the duration of cycle‐walking's encrypting process.” Copyright © 2012 John Wiley & Sons, Ltd.

Format Compliant Degradation for PNG Image

“…To resolve FCE for JPEG2000 bit stream, using cycle-walking method, Stütz had proposed a block-based cycle-walking algorithm, but it is not suitable for other image formats including PNG. Especially, [11] analyzed the inefficiency for cycle-walking method.…”