Biclique cryptanalysis on lightweight block cipher: HIGHT and Piccolo

Biclique cryptanalysis is an attack that improves the computational complexity by finding a biclique which is a kind of bipartite graph. We present a single-key full-round attack of lightweight block ciphers, HIGHT and Piccolo by using biclique cryptanalysis. In this paper, a 9-round biclique is constructed for HIGHT and a 4-round biclique for Piccolo. These new bicliques are used to recover secret keys for the full rounds of HIGHT, Piccolo-80 and Piccolo-128, the computational complexity of 2^125.93, 2^79.34 and 2^127.36, respectively. The computational complexity of attacking HIGHT by a biclique cryptanalysis is reduced from 2^126.4. This is the first full-round attack on both Piccolo-80 and Piccolo-128.     

Multidimensional zero-correlation attacks on lightweight block cipher HIGHT: Improved cryptanalysis of an ISO standard

HIGHT is a block cipher designed in Korea with the involvement of Korea Information Security Agency. It was proposed at CHES 2006 for usage in lightweight applications such as sensor networks and RFID tags. Lately, it has been adopted as ISO standard. Though there is a great deal of cryptanalytic results on HIGHT, its security evaluation against the recent zero-correlation linear attacks is still lacking. At the same time, the Feistel-type structure of HIGHT suggests that it might be susceptible to this type of cryptanalysis. In this paper, we aim to bridge this gap.We identify zero-correlation linear approximations over 16 rounds of HIGHT. Based upon those, we attack 27-round HIGHT (round 4 to round 30) with improved time complexity and practical memory requirements. This attack of ours is the best result on HIGHT to date in the classical single-key setting. We also provide the first attack on 26-round HIGHT (round 4 to round 29) with the full whitening key.     

Q的线性密码分析

对NESSIE公布的17个分组密码之一的Q进行了线性密码分析,攻击所需的数据复杂不大于2^118(相应的成功率为0．785）,空间复杂度不大于2^33 2^19 2^18 2^12 2^11 2^10。此结果显示Q对线性密码分析是不免疫的。     

Practical security against linear cryptanalysis for SMS4-like ciphers with SP round function

SMS4,a block cipher whose global structure adopts a special unbalanced Feistel scheme with SP round function,is accepted as the Chinese National Standard for securing Wireless LANs.In this paper,in order to evaluate the security against linear cryptanalysis,we examine the upper bound of the maximum linear characteristic probability of SMS4-like ciphers with SP round function.In the same way as for SPN ciphers,it is sufficient to consider the lower bound of the number of linear active s-boxes.We propose a formula to compute the lower bound of the number of linear active s-boxes with regard to the number of rounds.The security threshold of SMS4-like ciphers can be estimated easily with our result.Furthermore,if the number of input words in each round of SMS4-like cipher is m,we find that it is unnecessary for designers to make the linear branch number of P greater than 2 m with respect to linear cryptanalysis.     

Improved Linear Attacks on the Chinese Block Cipher Standard

The block cipher used in the Chinese Wireless LAN Standard （WAPI）, SMS4, was recently renamed as SM4, and became the block cipher standard issued by the Chinese government. This paper gives a method for finding the linear approximations of SMS4. With this method, 19-round one-dimensional approximations are given, which are used to improve the previous linear cryptanalysis of SMS4. The 19-round approximations hold with bias 2-62.27; we use one of them to leverage a linear attack on 23-round SMS4. Our attack improves the previous 23-round attacks by reducing the time complexity. Furthermore, the data complexity of our attack is further improved by the multidimensional linear approach.     

Improved Linear Cryptanalysis of CAST-256

CAST-256, a first-round AES (Advanced Encryption Standard) candidate, is designed based on CAST-128. It is a 48-round Generalized-Feistel-Network cipher with 128-bit block accepting 128, 160, 192, 224 ...     

Impossible differential cryptanalysis of advanced encryption standard

Impossible differential cryptanalysis is a method recovering secret key, which gets rid of the keys that satisfy impossible differential relations. This paper concentrates on the impossible differential cryptanalysis of Advanced Encryption Standard (AES) and presents two methods for impossible differential cryptanalysis of 7-round AES-192 and 8-round AES-256 combined with time-memory trade-off by exploiting weaknesses in their key schedule. This attack on the reduced to 7-round AES-192 requires about 294.5 chosen plaintexts, demands 2129 words of memory, and performs 2157 7-round AES-192 encryptions. Furthermore, this attack on the reduced to 8-round AES-256 requires about 2101 chosen plaintexts, demands 2201 words of memory, and performs 2228 8-round AES-256 encryptions.     

针对简化版Trivium算法的线性分析

流密码Trivium算法是欧洲密码工程eSTREAM的7个最终获选算法之一.该文针对初始化为288轮的简化版Trivium算法进行了线性分析,更正了Turan等人给出的关于密钥、初始化向量和密钥流比特的表达式,并给出了当允许选取特殊的密钥和Ⅳ时,搜索最佳线性逼近式的算法.据此算法,找到了3个线性偏差为2-25的线性逼近式,改进了Turan等人给出的线性偏差为2-31的线性分析结果.     

Zodiac密码算法的多维零相关线性分析

分组密码算法Zodiac支持3种密钥长度,分别为Zodiac-128、Zodiac-192、Zodiac-256。利用零相关线性分析方法评估了Zodiac算法的安全性,首先根据算法的结构特性,构造了一些关于Zodiac算法的10轮零相关线性逼近,然后对16轮Zodiac-192进行了多维零相关分析。分析结果显示：攻击过程中一共恢复了19个字节的密钥,其数据复杂度约为2^124.40个明密文对,计算复杂度为2^181.58次16轮加密。由此可得：16轮（即全轮）192 bit密钥的Zodiac算法（Zodiac-192）对于零相关线性分析方法是不安全的。     

多重线性密码分析中线性逼近方程的构造

到目前为止,还没有利用构造多个逼近方程来实现B.S.Kaliski和M.J.B.Robshaw的多重线性逼近的例子.本文利用Mastui构造的线性组合传递链是周期为8的线性组合传递链这个特点,选取该线性组合传递链的8个不同起点,就可由该线性组合传递链构造出8条新的线性组合传递链,再加上其对偶的线性组合传递链,共可构造出16条线性组合传递链,利用它们可实现对DES的密钥比特进行攻击.     

Differential attack on nine rounds of the SEED block cipher

The SEED block cipher has a 128-bit block length, a 128-bit user key and a total number of 16 rounds. It is an ISO international standard. In this letter, we describe two 7-round differentials with a trivially larger probability than the best previously known one on SEED, and present a differential cryptanalysis attack on a 9-round reduced version of SEED. The attack requires a memory of 2^69.71 bytes, and has a time complexity of 2^126.36 encryptions with a success probability of 99.9% when using 2¹²⁵ chosen plaintexts, or a time complexity of 2^125.36 encryptions with a success probability of 97.8% when using 2¹²⁴ chosen plaintexts. Our result is better than any previously published cryptanalytic results on SEED in terms of the numbers of attacked rounds, and it suggests for the first time that the safety margin of SEED decreases below half of the number of rounds.     

What is the effective key length for a block cipher: an attack on every practical block cipher

Recently,several important block ciphers are considered to be broken by the brute-force-like cryptanalysis,with a time complexity faster than the exhaustive key search by going over the entire key space but performing less than a full encryption for each possible key.Motivated by this observation,we describe a meetin-the-middle attack that can always be successfully mounted against any practical block ciphers with success probability one.The data complexity of this attack is the smallest according to the unicity distance.The time complexity can be written as 2k(1-),where>0 for all practical block ciphers.Previously,the security bound that is commonly accepted is the length k of the given master key.From our result we point out that actually this k-bit security is always overestimated and can never be reached because of the inevitable loss of the key bits.No amount of clever design can prevent it,but increments of the number of rounds can reduce this key loss as much as possible.We give more insight into the problem of the upper bound of effective key bits in block ciphers,and show a more accurate bound.A suggestion about the relationship between the key size and block size is given.That is,when the number of rounds is fixed,it is better to take a key size equal to the block size.Also,effective key bits of many well-known block ciphers are calculated and analyzed,which also confirms their lower security margins than thought before.The results in this article motivate us to reconsider the real complexity that a valid attack should compare to.     

一类基于混沌函数的分组密码的安全性评估

评估了一类基于混沌函数的分组密码(generalized Feistel structure,简称GFS)抵抗差分密码分析和线性密码分析的能力.如果轮函数是双射且它的最大差分特征概率和线性逼近概率分别是p和q,则r轮GFS的最大差分特征和线性逼近的概率分别以p^r-1和q^r-1为其上界.     

Chaos block cipher for wireless sensor network

New block cipher algorithm in single byte for wireless sensor network with excellence of many cipher algorithms is studied. The child keys are generated through the developed discrete Logistic mapping, and the Feistel encrypting function with discrete chaos operation is constructed. The single byte block is encrypted and decrypted through one turn permutation, being divided into two semi-byte, quadri- Feistel structural operation, and one turn permutation again. The amount of keys may be variable with the turns of Feistel structural operation. The random and security of the child key was proven, and the experiment for the block cipher in wireless sensor network was completed. The result indicates that the algorithm is more secure and the chaos block cipher in single byte is feasible for wireless sensor network.     

On computational complexity of impossible differential cryptanalysis

Impossible differential cryptanalysis is one of the conventional methods in the field of cryptanalysis of block ciphers. In this paper, a general model of an impossible differential attack is introduced. Then, according to this model, the concept of an ideal impossible differential attack is defined and it is proven that the time complexity of an ideal attack only depends on the number of involved round key bits in the attack.     

演化密码对抗多重线性密码分析能力的研究

演化密码是我国学者提出的一种新型密码.文中对演化密码对抗多重线性密码分析的能力进行研究,研究表明演化密码对抗多重线性攻击方面的能力高于普通固定算法密码.文中介绍了基于对数似然比(LLR)统计方法的两种多重线性密码分析方法,这两种方法利用多个线性逼近式分别扩展了Matsui最初提出的线性攻击算法1和算法2.在考察这两种算法的数据复杂度N、比特优势a,以及预期成功率PS三者关系的基础上,证明了在比特优势和预期成功率相同的条件下,攻击演化密码的数据复杂度大于攻击固定算法密码的数据复杂度,并论述了在数据复杂度N相同的情况下,攻击演化密码的时间复杂度和空间复杂度都明显高于攻击固定算法密码的情形.这表明演化密码在对抗多重线性攻击方面的安全性高于固定算法密码.