• Journal of the Korea Institute of Information Security & Cryptology
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• v.27 no.6
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• pp.1261-1269
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• 2017

Feistel Networks are one of the most well-known schemes to design block ciphers. Generalized Feistel Networks are used to construct only block ciphers but also hash functions. Many generic attacks on Feistel schemes have been studied. Among these attacks, recently proposed meet-in-the-middle attacks are one of the most effective attacks. In this paper, we analyze the security of meet-in-the-middle attacks on generalized Feistel Networks.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.19 no.2
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• pp.3-9
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• 2009

In this paper we introduce a new side-channel attack using block cipher cryptanalysis named meet-in-the middle attack. Using our new side-channel technique we introduce side-channel attacks on AES with reduced masked rounds. That is, we show that AES with reduced 10 masked rounds is vulnerable to side channel attacks based on an existing 4-round function. This shows that one has to mask the entire rounds of the 12-round 192-bit key AES to prevent our attacks. Our results are the first ones to analyze AES with reduced 10 masked rounds.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.5
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• pp.2660-2679
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• 2017

Crypton is a SP-network block cipher that attracts much attention because of its excellent performance on hardware. Based on Crypton, mCrypton is designed as a lightweight block cipher suitable for Internet of Things (IoT) and Radio Frequency Identification (RFID). The security of Crypton and mCrypton under meet-in-the-middle attack is analyzed in this paper. By analyzing the differential properties of cell permutation, several differential characteristics are introduced to construct generalized ${\delta}-sets$. With the usage of a generalized ${\delta}-set$ and differential enumeration technique, a 6-round meet-in-the-middle distinguisher is proposed to give the first meet-in-the-middle attack on 9-round Crypton-192 and some improvements on the cryptanalysis of 10-round Crypton-256 are given. Combined with the properties of nibble permutation and substitution, an improved meet-in-the-middle attack on 8-round mCrypton is proposed and the first complete attack on 9-round mCrypton-96 is proposed.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.2
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• pp.727-746
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• 2018

The hash function RIPEMD-160 is a worldwide ISO/IEC standard and the hash function HAS-160 is the Korean hash standard and is widely used in Korea. On the basis of differential meet-in-the-middle attack and biclique technique, a preimage attack on 34-step RIPEMD-160 with message padding and a pseudo-preimage attack on 71-step HAS-160 without message padding are proposed. The former is the first preimage attack from the first step, the latter increases the best pseudo-preimage attack from the first step by 5 steps. Furthermore, we locate the linear spaces in another message words and exchange the bicliques construction process and the mask vector search process. A preimage attack on 35-step RIPEMD-160 and a preimage attack on 71-step HAS-160 are presented. Both of the attacks are from the intermediate step and satisfy the message padding. They improve the best preimage attacks from the intermediate step on step-reduced RIPEMD-160 and HAS-160 by 4 and 3 steps respectively. As far as we know, they are the best preimage and pseudo-preimage attacks on step-reduced RIPEMD-160 and HAS-160 respectively in terms of number of steps.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.14 no.3
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• pp.118-124
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• 2004

KASUMI is a 64-bit iterated block cipher with a 128-bit key size and 8 rounds Feistel structure. In this paper, we describe saturation attacks on the five round KASUMI, which requires 10 $\times$$2^{32}$ chosen plaintexts and $2^{115}$ computational complexity We also improve this attack using meet-in-the-middle technique. This attack requires 7$\times$$2^{32}$ chosen plaintexts and $2^{90}$ computational complexity. Futhermore, we attack KASUMI by controlling the value of the fixed part of the key. This attack needs 3$\times$$2^{32}$ chosen plaintexts and $2^{57}$ computational complexity.

• Journal of the Optical Society of Korea
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• v.19 no.6
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• pp.592-603
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• 2015

In this paper, an optical implementation of a novel asymmetrical cryptosystem combined with D-H secret key sharing and triple DES is proposed. The proposed optical cryptosystem is realized by performing free-space interconnected optical logic operations such as AND, OR and XOR which are implemented in Mach-Zehnder type interferometer architecture. The advantage of the proposed optical architecture provides dual outputs simultaneously, and the encryption optical setup can be used as decryption optical setup only by changing the inputs of SLMs. The proposed cryptosystem can provide higher security strength than the conventional electronic algorithm, because the proposed method uses 2-D array data, which can increase the key length surprisingly and uses 3DES algorithm, which protects against “meet in the middle” attacks. Another advantage of the proposed asymmetrical cryptosystem is that it is free to change the user’s two private random numbers in generating the public keys at any time. Numerical simulation and performance analysis verify that the proposed asymmetric cryptosystem is effective and robust against attacks for the asymmetrical cipher system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.9
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• pp.4727-4741
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• 2019

The lightweight block cipher Piccolo adopts Generalized Feistel Network structure with 64 bits of block size. Its key supports 80 bits or 128 bits, expressed by Piccolo-80 or Piccolo-128, respectively. In this paper, we exploit the security of reduced version of Piccolo from the first round with the pre-whitening layer, which shows the vulnerability of original Piccolo. As a matter of fact, we first study some linear relations among the round subkeys and the properties of linear layer. Based on them, we evaluate the security of Piccolo-80/128 against the meet-in-the-middle attack. Finally, we attack 13 rounds of Piccolo-80 by applying a 5-round distinguisher, which requires $2^{44}$ chosen plaintexts, $2^{67.39}$ encryptions and $2^{64.91}$ blocks, respectively. Moreover, we also attack 17 rounds of Piccolo-128 by using a 7-round distinguisher, which requires $2^{44}$ chosen plaintexts, $2^{126}$ encryptions and $2^{125.49}$ blocks, respectively. Compared with the previous cryptanalytic results, our results are the currently best ones if considering Piccolo from the first round with the pre-whitening layer.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.19 no.3
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• pp.3-10
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• 2009

In this paper, we introduce improved differential and linear attacks on the SMS4 block cipher which is used in the Chinese national standard WAPI (WLAN Authentication and Privacy Infrastructure, WLAN - Wireless Local Area Network): First, we introduce how to extend previously known differential attacks on SMS4 from 20 or 21 to 22 out of the full 32 rounds. Second, we improve a previously known linear attack on 22-round reduced SMS4 from $2^{119}$ known plaintexts, $2^{109}$ memory bytes, $2^{117}$ encryptions to $2^{117}$ known plaintexts, $2^{l09}$ memory bytes, $2^{112.24}$ encryptions, by using a new linear approximation.