Elastic block ciphers: the basic design
ASIACCS '07 Proceedings of the 2nd ACM symposium on Information, computer and communications security
Methods for Linear and Differential Cryptanalysis of Elastic Block Ciphers
ACISP '08 Proceedings of the 13th Australasian conference on Information Security and Privacy
A note on Cook's elastic block cipher
Proceedings of the 4th International Symposium on Information, Computer, and Communications Security
The security of elastic block ciphers against key-recovery attacks
ISC'07 Proceedings of the 10th international conference on Information Security
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Standard block ciphers are designed around one or a small number of block sizes. From both a practical and a theoretical perspective, the question of how to efficiently support a range of block sizes is of interest. In applications, the length of the data to be encrypted is often not a multiple of the supported block size. This results in the use of plaintext-padding schemes that impose computational and space overheads. Furthermore, a variable-length block cipher ideally provides a variable-length pseudorandom permutation and strong pseudorandom permutation, which are theoretical counterparts of practical block ciphers and correspond to ideal properties for a block cipher. The focus of my research is the design and analysis of a method for creating variable-length block ciphers from existing fixed-length block ciphers. As the heart of the method, I introduce the concept of an elastic block cipher, which refers to stretching the supported block size of a block cipher to any length up to twice the original block size while incurring a computational workload that is proportional to the block size. I create a structure, referred to as the elastic network, that uses the round function from any existing block cipher in a manner that allows the properties of the round function to be maintained and results in the security of the elastic version of a block cipher being directly related to that of the original version. By forming a reduction between the elastic and original versions, I prove that the elastic version of a cipher is secure against round-key recovery attacks if the original cipher is secure against such attacks. I illustrate the method by creating elastic versions of four existing block ciphers. In addition, the elastic network provides a new primitive structure for use in symmetric-key cipher design. It allows for the creation of variable-length pseudorandom permutations and strong pseudorandom permutations in the range of b to 2b bits from round functions that are independently chosen pseudorandom permutations on b bits.