Collision attack

About: Collision attack is a research topic. Over the lifetime, 1093 publications have been published within this topic receiving 28389 citations.

Improved Cryptanalysis of Reduced RIPEMD-160

Abstract: In this article, we propose an improved cryptanalysis of the double-branch hash function standard RIPEMD-160. Using a carefully designed non-linear path search tool, we study the potential differential paths that can be constructed from a difference in a single message word and show that some of these message words can lead to very good differential path candidates. Leveraging the recent freedom degree utilization technique from Landelle and Peyrin to merge two branch instances, we eventually manage to obtain a semi-free-start collision attack for 42 steps of the RIPEMD-160 compression function, while the previously best know result reached 36 steps. In addition, we also describe a 36-step semi-free-start collision attack which starts from the first step.

Producing collisions for PANAMA, instantaneously

Abstract: We present a practical attack on the Panama hash function that generates a collision in 26 evaluations of the state updating function. Our attack improves that of Rijmen and coworkers that had a complexity 282, too high to produce a collision in practice. This improvement comes mainly from the use of techniques to transfer conditions on the state to message words instead of trying many message pairs and using the ones for which the conditions are satisfied. Our attack works for any arbitrary prefix message, followed by a pair of suffix messages with a given difference. We give an example of a collision and make the collision-generating program available. Our attack does not affect the Panama stream cipher, that is still unbroken to the best of our knowledge.

Analysis and Improvement of Differential Computation Attacks against Internally-Encoded White-Box Implementations

Abstract: White-box cryptography is the last security barrier for a cryptographic software implementation deployed in an untrusted environment. The principle of internal encodings is a commonly used white-box technique to protect block cipher implementations. It consists in representing an implementation as a network of look-up tables which are then encoded using randomly generated bijections (the internal encodings). When this approach is implemented based on nibble (i.e. 4-bit wide) encodings, the protected implementation has been shown to be vulnerable to differential computation analysis (DCA). The latter is essentially an adaptation of differential power analysis techniques to computation traces consisting of runtime information, e.g., memory accesses, of the target software. In order to thwart DCA, it has then been suggested to use wider encodings, and in particular byte encodings, at least to protect the outer rounds of the block cipher which are the prime targets of DCA.In this work, we provide an in-depth analysis of when and why DCA works. We pinpoint the properties of the target variables and the encodings that make the attack (in)feasible. In particular, we show that DCA can break encodings wider than 4-bit, such as byte encodings. Additionally, we propose new DCA-like attacks inspired from side-channel analysis techniques. Specifically, we describe a collision attack particularly effective against the internal encoding countermeasure. We also investigate mutual information analysis (MIA) which naturally applies in this context. Compared to the original DCA, these attacks are also passive and they require very limited knowledge of the attacked implementation, but they achieve significant improvements in terms of trace complexity. All the analyses of our work are experimentally backed up with various attack simulation results. We also verified the practicability of our analyses and attack techniques against a publicly available white-box AES implementation protected with byte encodings –which DCA has failed to break before– and against a “masked” white-box AES implementation –which intends to resist DCA.

New Collision Attacks on Round-Reduced Keccak.

Abstract: In this paper, we focus on collision attacks against Keccak hash function family and some of its variants. Following the framework developed by Dinur et al. at FSE 2012 where 4-round collisions were found by combining 3-round differential trails and 1-round connectors, we extend the connectors one round further hence achieve collision attacks for up to 5 rounds. The extension is possible thanks to the large degree of freedom of the wide internal state. By linearization of all S-boxes of the first round, the problem of finding solutions of 2-round connectors are converted to that of solving a system of linear equations. However, due to the quick freedom reduction from the linearization, the system has solution only when the 3-round differential trails satisfy some additional conditions. We develop a dedicated differential trail search strategy and find such special differentials indeed exist. As a result, the first practical collision attack against 5-round SHAKE128 and two 5-round instances of the Keccak collision challenges are found with real examples. We also give the first results against 5-round Keccak-224 and 6-round Keccak collision challenges. It is remarked that the work here is still far from threatening the security of the full 24-round Keccak family.

An Attack Against Message Authentication in the ERTMS Train to Trackside Communication Protocols

Abstract: This paper presents the results of a cryptographic analysis of the protocols used by the European Rail Traffic Management System (ERTMS). A stack of three protocols secures the communication between trains and trackside equipment; encrypted radio communication is provided by the GSM-R protocol, on top of this the EuroRadio protocol provides authentication for a train control application-level protocol. We present an attack which exploits weaknesses in all three protocols: GSM-R has the same well known weaknesses as the GSM protocol, and we present a new collision attack against the EuroRadio protocol. Combined with design weaknesses in the application-level protocol, these vulnerabilities allow an attacker, who observes a MAC collision, to forge train control messages. We demonstrate this attack with a proof of concept using train control messages we have generated ourselves. Currently, ERTMS is only used to send small amounts of data for short sessions, therefore this attack does not present an immediate danger. However, if EuroRadio was to be used to transfer larger amounts of data trains would become vulnerable to this attack. Additionally, we calculate that, under reasonable assumptions, an attacker who could monitor all backend control centres in a country the size of the UK for 45 days would have a 1% chance of being able to take control of a train.