63 chosen plaintext pairs are required. (c) The encryption/decryption speed of the n-round RDES is almost the same as that of the n-round DES." />


Dynamic Swapping Schemes and Differential Cryptanalysis

Toshinobu KANEKO  Kenji KOYAMA  Routo TERADA  

Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E77-A   No.8   pp.1328-1336
Publication Date: 1994/08/25
Online ISSN: 
DOI: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Information Theory and Its Applications)
Category: 
Keyword: 
differential cryptanalysis,  secret key cryptosystem,  DES,  characteristic probability,  dynamic swapping scheme,  

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Summary: 
This paper proposes a dynamically randomized version of DES (called RDES) in which a input-dependent swapping Sk(X) is added onto the right half of the input in each round of DES. This new scheme decreases the probability of success in differential cryptanalysis because it decreases the characteristic probability. Each "best" two-round characteristic probability is analyzed for typical schemes of the RDES: (i) RDES-1 with a simple one-level swapping, (ii) RDES-1' with an optimal one-level swapping, (iii) RDES-2 with a simple two-level swapping, and (iv) RDES-2' with an optimal two-level swapping. The main results are as follows. (a) The differential attacks on the 16-round RDES-1' and the 16-round RDES-2 require more computational time than the exhaustive search. (b) A differential attack is substantially inapplicable to the 16-round RDES-2' because more than 263 chosen plaintext pairs are required. (c) The encryption/decryption speed of the n-round RDES is almost the same as that of the n-round DES.