30 research outputs found

    Could The 1-MSB Input Difference Be The Fastest Collision Attack For MD5 ?

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    So far, two different 2-block collision differentials, both with 3-bit input differences for MD5, have been found by Wang etc in 2005 and Xie etc in 2008 respectively, and those differentials have been improved later on to generate a collision respectively within around one minute and half an hour on a desktop PC. Are there more collision differentials for MD5? Can a more efficient algorithm be developed to find MD5 collisions? In this paper, we list the whole set of 1-bit to 3-bit input difference patterns that are possibly qualified to construct a feasible collision differential, and from which a new collision differential with only 1-MSB input difference is then analyzed in detail, finally the performances are compared with the prior two 3-bit collision attacks according to seven criteria proposed in this paper. In our approach, a two-block message is still needed to produce a collision, the first block being only one MSB different while the second block remains the same. Although the differential path appears to be computationally infeasible, most of the conditions that a collision differential path must satisfy can be fulfilled by multi-step modifications, and the collision searching efficiency can be much improved further by a specific divide-and-conquer technique, which transforms a multiplicative accumulation of the computational complexities into an addition by properly grouping of the conditional bits. In particular, a tunneling-like technique is applied to enhance the attack algorithm by introducing some additional conditions. As a result, the fastest attack algorithm is obtained with an averaged computational complexity of 2^20.96 MD5 compressions, which implies that it is able to search a collision within a second on a common PC for arbitrary random initial values. With a reasonable probability a collision can be found within milliseconds, allowing for instancing an attack during the execution of a practical protocol. The collision searching algorithm, however, is very complex, but the algorithm has been implemented which is available from the website http://www.is.iscas.ac.cn/gnomon, and we suggest you download the implementation program from the website for a personal experience if you are interested in it

    A Meaningful MD5 Hash Collision Attack

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    It is now proved by Wang et al., that MD5 hash is no more secure, after they proposed an attack that would generate two different messages that gives the same MD5 sum. Many conditions need to be satisfied to attain this collision. Vlastimil Klima then proposed a more efficient and faster technique to implement this attack. We use these techniques to first create a collision attack and then use these collisions to implement meaningful collisions by creating two different packages that give identical MD5 hash, but when extracted, each gives out different files with contents specified by the atacker

    Improved cryptanalysis of skein

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    The hash function Skein is the submission of Ferguson et al. to the NIST Hash Competition, and is arguably a serious candidate for selection as SHA-3. This paper presents the rst third-party analysis of Skein, with an extensive study of its main component: the block cipher Three sh. We notably investigate near collisions, distinguishers, impossible di erentials, key recovery using related-key di erential and boomerang attacks. In particular, we present near collisions on up to 17 rounds, an impossible di erential on 21 rounds, a related-key boomerang distinguisher on 34 rounds, a known-related-key boomerang distinguisher on 35 rounds, and key recovery attacks on up to 32 rounds, out of 72 in total for Threefish-512. None of our attacks directly extends to the full Skein hash. However, the pseudorandomness of Threefish is required to validate the security proofs on Skein, and our results conclude that at least 3

    Construct MD5 Collisions Using Just A Single Block Of Message

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    So far, all the differential attacks on MD5 were constructed through multi-block collision method. Can collisions for MD5 be found using just a single block of message (i.e. 512-bit)? This has been an open problem since the first 2-block collision attack was given. Today, in the last month (Dec,) of 2010, we have to make public a result of our 1-block collision attacks on MD5 in Table 1 as below, which was actually obtained at the beginning of 2010, but for security reasons, the techniques are not allowed to be disclosed at the moment. Here, we are calling for a challenge to the cryptology community that, any one who first gives a new different 1-block collision attack on MD5 will win 10,000 US dollars (about 50,000 RMB in Chinese Yuan) as a reward for his (her) excellent work. This call for challenge will be ended on Jan 1st, 2013. This announcement’s first affiliated unit will be responsible for this amount of reward when a new different 1-block collision attack is received and verified

    On the Security of NMAC and Its Variants

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    Based on the three earlier MAC (Message Authentication Code) construction approaches, we propose and analyze some variants of NMAC. We propose  some key recovery attacks to  these  NMAC  variants, for  example, we can  recover  the  equivalent  inner  key  of NMAC  in  about O(2n/2) MAC  operations, in  a related key  setting. We  propose  NMAC-E, a  variant of NMAC  with  secret  envelop,  to  achieve  more  process  efficiency  and  no  loss  of security, which needs only one call to the  underlying hash  function, instead of two invocations in HMAC

    Chosen-Prefix Collisions for MD5 and Applications

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    We present a novel, automated way to find differential paths for MD5. Its main application is in the construction of \emph{chosen-prefix collisions}. We have shown how, at an approximate expected cost of 2392^{39} calls to the MD5 compression function, for any two chosen message prefixes PP and PP', suffixes SS and SS' can be constructed such that the concatenated values PSP\|S and PSP'\|S' collide under MD5. The practical attack potential of this construction of chosen-prefix collisions is of greater concern than the MD5-collisions that were published before. This is illustrated by a pair of MD5-based X.509 certificates one of which was signed by a commercial Certification Authority (CA) as a legitimate website certificate, while the other one is a certificate for a rogue CA that is entirely under our control (cf.\ \url{http://www.win.tue.nl/hashclash/rogue-ca/}). Other examples, such as MD5-colliding executables, are presented as well. More details can be found on \url{http://www.win.tue.nl/hashclash/ChosenPrefixCollisions/}

    Диференційний аналіз функцій хешування та блокових шифрів: узагальнений підхід

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    Differential analysis approaches are powerful block cipher analysis methods. Similar methods are used for hash function analysis. This paper generalizes differential analysis of unbalanced Feistel scheme based hash functions and Feistel block ciphers. Obtained results demonstrate, despite on some similarity of differential analysis for cipher and hash functions, they have crucial differences, so the same security parameters may belong to different resistances to differential analysis of cipher and hash functions. These results allow generate additional constrictions on security parameters in hash functions which are under development now.Методы дифференциального криптоанализа – мощные методы анализа блочных шифров. Для анализа функций хеширования, в частности функций на базе фейстелевских несбалансированных схем, также используются похожие методы. В данной статье обобщается дифференциальный анализ функций хеширования, основанных на несбалансированных схемах Фейстеля и блочных шифров на основе схем Фейстеля. Полученные результаты доказывают, что при схожести идей дифференциального анализа для блочных шифров и функций хеширования, они имеют существенные различия, благодаря которым, одинаковым параметрам безопасности отвечают разные стойкости к атакам с использованием дифференциального анализа для шифров и функций хеширования. Данные результаты также позволяют вырабатывать дополнительные ограничения на параметры безопасности при построении новых функций хеширования.Методи диференційного криптоаналізу є потужними методами аналізу блокових шифрів. Для аналізу функцій хешування, зокрема функцій на базі фейстелевських несбалансованих схем, також використовуються схожі методи. У даній статті узагальнюється диференційний криптоаналіз для функцій хешування, що базуються на несбалансованих схемах Фейстеля, та блокових шифрів на основі схем Фейстеля. Отримані результати доводять, що за подібності ідей диференційного аналізу блокових шифрів та функцій хешування, вони мають суттєві відмінності, завдяки яким, однаковим параметрам безпеки відповідають різні стійкості до атак з використанням диференційного аналізу для шифрів та функцій хешування. Дані результати також дозволяють виробляти додаткові обмеження на параметри безпеки при побудові нових функцій хешування

    Chosen-prefix collisions for MD5 and applications

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    We present a novel, automated way to find differential paths for MD5. Its main application is in the construction of chosen-prefix collisions. We have shown how, at an approximate expected cost of 239 calls to the MD5 compression function, for any two chosen message prefixes P and P', suffixes S and S' can be constructed such that the concatenated values P||S and P'||S' collide under MD5. The practical attack potential of this construction of chosen-prefix collisions is of greater concern than the MD5-collisions that were published before. This is illustrated by a pair of MD5-based X.509 certificates one of which was signed by a commercial Certification Authority (CA) as a legitimate website certificate, while the other one is a certificate for a rogue CA that is entirely under our control (cf. http://www.win.tue.nl/hashclash/rogue-ca/). Other examples, such as MD5-colliding executables, are presented as well. More details can be found on http://www.win.tue.nl/hashclash/ChosenPrefixCollisions/
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