Cryptology ePrint Archive: Report 2016/267

Improved Meet-in-the-Middle Attacks on Round-Reduced Crypton-256

Yonglin Hao

Abstract: The meet-in-the-middle (MITM) attack has prove to be efficient in analyzing the AES block cipher. Its efficiency has been increasing with the introduction of various techniques such as differential enumeration, key-dependent sieve, super-box etc. The recent MITM attack given by Li and Jin has successfully mounted to 10-round AES-256.

Crypton is an AES-like block cipher. In this paper, we apply the MITM method to the cryptanalysis of Crypton-256. Following Li and Jin's idea, we give the first 6-round distinguisher for Crypton. Based on the distinguisher as well as the properties of Crypton's simple key schedule, we successfully launch MITM attacks on Crypton-256 reduced to 9 and 10 rounds. For 9-round Crypton-256, our MITM attack can recover the 256-bit key with a time complexity $2^{173.05}$, a memory complexity $2^{241.17}$. For the 10-round version, we give two MITM attacks. The basic attack requires a time complexity $2^{240.01}$ and memory complexity $2^{241.59}$. The time/memory complexity of the advanced MITM attack on 10-round Crypton is $2^{245.05}/2^{209.59}$. Our MITM attacks share the same data complexity $2^{113}$ and their error rates are negligible.

Category / Keywords: secret-key cryptography / Cryptanalysis, Crypton, MITM, Efficient Differential Enumeration Technique, Key-Dependent Sieve, Super-Box

Date: received 8 Mar 2016, last revised 9 Mar 2016

Contact author: haoyl12 at mails tsinghua edu cn

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Version: 20160310:181007 (All versions of this report)

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