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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.

This paper develops analytical models for the avalanche characteristics of a class of block ciphers usually referred to as substitution-permutation encryption networks or SPNs. An SPN is considered to display good avalanche characteristics if a one bit change in the plaintext input is expected to result in close to half the ciphertext output bits changing. Good avalanche characteristics are important to ensure that a cipher is not susceptible to statistical attacks and the strength of an SPN's avalanche characteristics may be considered as a measure of the randomness of the ciphertext. The results presented in this paper demonstrate that the avalanche behaviour of encryption networks can be improved by using larger S-boxes. As well, it is shown that increasing the diffusion properties of the S-boxes or replacing the permutations by diffusive linear transformations is effective in improving the network avalanche characteristics.

In information security, message authentication is an

-In this paper, we introduce a new block cipher mode of operation targeted to providing high speed hardware-based self-synchronizing stream encryption. The proposed mode is a modification of statistical cipher feedback (SCFB) mode and is designed to be implemented using pipeline architectures for the block cipher. We refer to the mode as pipelined SCFB mode or PSCFB. In this paper, we consider the implementation characteristics and show that PSCFB is able to achieve speeds that are very close to pipelined block cipher implementations configured for counter mode. Such speeds are achieved with modest latency through the system and a small amount of memory required for the system queues with a provable guarantee of no queue overflow. Further, we examine the characteristics of PSCFB mode in response to bit errors and synchronization losses in the communication channel. Specifically, we show that the error propagation factor is modest and comparable to conventional SCFB and that synchronization recovery delay is reasonable given the expectation that synchronization loss is infrequent. Given the high efficiency and good communication characteristics of the mode, it is concluded that PSCFB is an excellent choice for high speed network applications requiring stream-oriented encryption with self-synchronizing capabilities.

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