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Paper Abstract and Keywords
Presentation 2009-07-03 10:45
On the strength evaluation of Lesamnta against differential cryptanalysis
Yasutaka Igarashi, Toshinobu Kaneko (Tokyo Univ. of Science) ISEC2009-28 SITE2009-20 ICSS2009-42
Abstract (in Japanese) (See Japanese page) 
(in English) We focus on the cryptographic hash algorithm Lesamnta-256, which is one of the
candidates for the new hash algorithm SHA-3. Lesamnta-256 consists of
the Merkle-Damg\r{a}rd iteration of a compression function. The
compression function consists of
a mixing function and a key scheduling function. The mixing function
consists of the 32 rounds of the four-way generalized Feistel structure.
There is a nonlinear function $F$ with 64-bit input/output on each
round, which consists of the 4 steps of AES type of SPN structure. A subkey
is XORed only at the first step of SPN. We analyze the security of
these components of Lesamnta as is,
although the designers analyzed its security by assuming that the subkey is
XORed at every step of SPN. We show that the 2 steps of SPN referred to
as XS have the maximum differential probability $2^{-11.415}$.
This probability is greater than both of the differential characteristic
probability $2^{-18}$ and the differential probability $2^{-12}$
derived under the independent subkey assumption. On the strength of
whole compression function, we show that there are at
least 15 active $F$ functions in the mixing function. As the input bit
width of the mixing function is 256, we can say that it is secure against differential attack if the maximum differential probability of $F$ function is less than
$2^{-256/15}$ = $2^{-17.067}$.
Finally we show that the key scheduling function is
secure against differential cryptanalysis.
Keyword (in Japanese) (See Japanese page) 
(in English) Lesamnta / differential cryptanalysis / higher-order differential / SHA-3 / hash function / / /  
Reference Info. IEICE Tech. Rep., vol. 109, no. 113, ISEC2009-28, pp. 147-152, July 2009.
Paper # ISEC2009-28 
Date of Issue 2009-06-25 (ISEC, SITE, ICSS) 
ISSN Print edition: ISSN 0913-5685    Online edition: ISSN 2432-6380
Copyright
and
reproduction
All rights are reserved and no part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. Notwithstanding, instructors are permitted to photocopy isolated articles for noncommercial classroom use without fee. (License No.: 10GA0019/12GB0052/13GB0056/17GB0034/18GB0034)
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Conference Information
Committee ISEC IPSJ-CSEC SITE ICSS  
Conference Date 2009-07-02 - 2009-07-03 
Place (in Japanese) (See Japanese page) 
Place (in English) Akita University 
Topics (in Japanese) (See Japanese page) 
Topics (in English)  
Paper Information
Registration To ISEC 
Conference Code 2009-07-ISEC-CSEC-SITE-ICSS 
Language Japanese 
Title (in Japanese) (See Japanese page) 
Sub Title (in Japanese) (See Japanese page) 
Title (in English) On the strength evaluation of Lesamnta against differential cryptanalysis 
Sub Title (in English)  
Keyword(1) Lesamnta  
Keyword(2) differential cryptanalysis  
Keyword(3) higher-order differential  
Keyword(4) SHA-3  
Keyword(5) hash function  
Keyword(6)  
Keyword(7)  
Keyword(8)  
1st Author's Name Yasutaka Igarashi  
1st Author's Affiliation Tokyo University of Science (Tokyo Univ. of Science)
2nd Author's Name Toshinobu Kaneko  
2nd Author's Affiliation Tokyo University of Science (Tokyo Univ. of Science)
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Speaker Author-1 
Date Time 2009-07-03 10:45:00 
Presentation Time 25 minutes 
Registration for ISEC 
Paper # ISEC2009-28, SITE2009-20, ICSS2009-42 
Volume (vol) vol.109 
Number (no) no.113(ISEC), no.114(SITE), no.115(ICSS) 
Page pp.147-152 
#Pages
Date of Issue 2009-06-25 (ISEC, SITE, ICSS) 


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