Analysis of the statistical cipher feedback mode of block ciphers

Abstract

In this paper, we examine a recently proposed mode of operation for block ciphers which we refer to as statistical cipher feedback (SCFB) mode. SCFB mode configures the block cipher as a keystream generator for use in a stream cipher such that it has the property of statistical self-synchronization, thereby allowing the stream cipher to recover from bit slips in the communication channel. Statistical self-synchronization involves feeding back ciphertext to the input of the block cipher similar to the conventional cipher feedback (CFB) mode, except that the feedback only occurs when a special synchronization pattern is recognized in the ciphertext. In the paper, we examine the efficiency, resynchronization, and error propagation characteristics of SCFB and compare these to conventional modes such as CFB and output feedback (OFB). In particular, we study these characteristics of SCFB as a function of the synchronization pattern size. As well, we examine implementation issues of SCFB, focusing on the buffer requirements and resulting delay for a practical realization of the cipher. We conclude that SCFB mode can be used to provide practical, efficient, self-synchronizing implementations for stream ciphers. In particular, SCFB mode is best used in circumstances where slips are a concern and where implementation efficiency is a high priority in comparison to encryption latency.

Pipelined Statistical Cipher Feedback: A New Mode for High-Speed Self-Synchronizing Stream Encryption

“…Upon resynchronization, the system obtains an IV block from the ciphertext to reload the counter value; otherwise the input to the block cipher is taken directly to be the counter value, which is incremented for every block cipher operation. Such a construction has the same basic characteristics of OFB-based SCFB discussed in [3]. As we shall see, using counter mode in the SCFB configuration is consistent with the new mode described in this paper.…”

“…To overcome the speed limitations of CFB, SCFB mode has been proposed [2] and analyzed [3]. Further analysis of a slightly modified version of SCFB is presented in [11].…”

“…through bit slips caused by timing errors). The mode presented in this paper is an extension of the concept of statistical self-synchronization introduced in [2] and analyzed in [3]. A typical application for the mode presented in this paper is stream-oriented physical layer communication where high speeds are required and where it is possible for timing errors or other network faults to lead to synchronization losses.…”

A Novel Structure with Dynamic Operation Mode for Symmetric-Key Block Ciphers

“…In CFB decryption, the required forward cipher operations can be performed in parallel if the input blocks are first constructed (in series) from the ciphertext [18].…”

The Unified Operation Structure for Symmetric-Key Algorithm

“…In CFB decryption, the required forward cipher operations can be performed in parallel if the input blocks are first constructed (in series) from the ciphertext [14].…”