Modes of operation adapt block ciphers to many applications. Among the encryption modes, only CFB (Cipher Feedback) has both of the following properties: Firstly it allows transmission units shorter than the block-cipher length to be encrypted and sent without delay and message expansion. Secondly, it can resynchronize after the loss of such transmission units. However, CFB is inefficient in such applications, since for every transmission unit, regardless how short, a call to the block cipher is needed. We propose a new mode of operation based on CFB which remedies this problem. Our proposal, OCFB, is almost optimally efficient (i.e., almost as many message bits are encrypted as block-cipher output bits produced) and it can self-synchronize after the loss or insertion of transmission units. We prove the security of CFB and OCFB in the sense of modern cryptography.

No abstract

No abstract

No abstract

Abstract. Structuring and reuse are key approaches to the proper development and maintenance of software systems. System structuring is essential to controlling complexity, and is a prerequisite for the extraction of reuse artifacts. Reuse of solutions is crucial to controlling quality and productivity. In previous work, we have identified and applied the structuring unit micro protocol. We extend these results by defining a flexible micro protocol framework, and by applying it to the design of a functionally complete communication system, with SDL as design language.