There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

National Institute of Standards and Technology における超伝導研究及び生活

We present a new block cipher LED. While dedicated to compact hardware implementation, and offering the smallest silicon footprint among comparable block ciphers, the cipher has been designed to simultaneously tackle three additional goals. First, we explore the role of an ultra-light (in fact non-existent) key schedule. Second, we consider the resistance of ciphers, and LED in particular, to related-key attacks: we are able to derive simple yet interesting AES-like security proofs for LED regarding related- or single-key attacks. And third, while we provide a block cipher that is very compact in hardware, we aim to maintain a reasonable performance profile for software implementation.

The LED block cipher

Smart grids equipped with bi-directional communication flow are expected to provide more sophisticated consumption monitoring and energy trading. However, the issues related to the security and privacy of consumption and trading data present serious challenges. In this paper we address the problem of providing transaction security in decentralized smart grid energy trading without reliance on trusted third parties. We have implemented a proof-of-concept for decentralized energy trading system using blockchain technology, multi-signatures, and anonymous encrypted messaging streams, enabling peers to anonymously negotiate energy prices and securely perform trading transactions. We conducted case studies to perform security analysis and performance evaluation within the context of the elicited security and privacy requirements.

Security and Privacy in Decentralized Energy Trading Through Multi-Signatures, Blockchain and Anonymous Messaging Streams

Since Rijndael was chosen as the Advanced Encryption Standard (AES), improving upon 7-round attacks on the 128-bit key variant (out of 10 rounds) or upon 8-round attacks on the 192/256-bit key variants (out of 12/14 rounds) has been one of the most difficult challenges in the cryptanalysis of block ciphers for more than a decade. In this paper, we present the novel technique of block cipher cryptanalysis with bicliques, which leads to the following results:

 

The first key recovery method for the full AES-128 with computational complexity 2126.1.

The first key recovery method for the full AES-192 with computational complexity 2189.7.

The first key recovery method for the full AES-256 with computational complexity 2254.4.

Key recovery methods with lower complexity for the reduced-round versions of AES not considered before, including cryptanalysis of 8-round AES-128 with complexity 2124.9.

Preimage search for compression functions based on the full AES versions faster than brute force.

In contrast to most shortcut attacks on AES variants, we do not need to assume related-keys. Most of our techniques only need a very small part of the codebook and have low memory requirements, and are practically verified to a large extent. As our cryptanalysis is of high computational complexity, it does not threaten the practical use of AES in any way.

/pdf/biclique-cryptanalysis-of-the-full-aes-pi8uwf8n7d.pdf

Biclique cryptanalysis of the full AES

In this paper, we present a semi-free-start collision attack on the compression function for all Twister variants with negligible complexity. We show how this compression function attack can be extended to construct collisions for Twister-512 slightly faster than brute force search. Furthermore, we present a second-preimage and preimage attack for Twister-512 with complexity of about 2384 and 2456 compression function evaluations, respectively.

https://lirias.kuleuven.be/bitstream/123456789/329822/2/article-2102.pdf

Cryptanalysis of Twister

HAS-160 is an iterated cryptographic hash function that is widely used in Korea. In this article, we present a collision attack on the hash function HAS-160 reduced to 53-steps. The attack has a complexity of about 235 hash computations. It is based on the work of Cho et al. presented at ICISC 2006. We improve the attack complexity of Cho et al. by a factor of about 220 using a slightly different strategy for message modification in the first 20 steps of the hash function and present the first actual colliding message pair for 53-step HAS-160. Furthermore, we show how the attack can be extended to 59-step HAS-160 by using a characteristic spanning over two message blocks.

Colliding message pair for 53-step HAS-160

SIMD is one of the round 2 candidates of the public SHA-3 competition hosted by NIST. It was designed by Leurent et al.. In this paper, we present a distinguisher attack on the compression function of SIMD-512. By linearizing the compression function we construct a linear code. Using techniques from coding theory to search for low Hamming weight codewords, we can find differential characteristics with low Hamming weight (and hence high probability). In the attack the differences are introduced only in the IV. Such a characteristic is the base for our distinguisher, which can distinguish the compression function of SIMD-512 from random with a complexity of 5·2425.28 compression function calls. Furthermore, we can distinguish the output transformation of SIMD-512 from random with a complexity of about 22·2425.28 compression function calls. So far this is the first cryptanalytic result for the SIMD hash function.

/pdf/a-distinguisher-for-the-compression-function-of-simd-512-xidkmkykxv.pdf

A Distinguisher for the Compression Function of SIMD-512

FORK-256 is a hash function presented at FSE 2006. Whereas SHA-like designs process messages in one stream, FORK-256 uses four parallel streams for hashing. In this article, we present the first cryptanalytic results on this design strategy. First, we study a linearized variant of FORK-256, and show several unusual properties of this linearized variant. We also explain why the linearized model can not be used to mount attacks similar to the recent attacks by Wang et al. on SHA-like hash functions. Second, we show how collision attacks, exploiting the non-bijectiveness of the nonlinear functions of FORK-256, can be mounted on reduced variants of FORK-256. We show an efficient attack on FORK-256 reduced to 2 streams and present actual colliding pairs. We expect that our attack can also be extended to FORK-256 reduced to 3 streams. For the moment our approach does not appear to be applicable to the full FORK-256 hash function.

/pdf/cryptanalysis-of-reduced-variants-of-the-fork-256-hash-2fts0oddit.pdf

Cryptanalysis of reduced variants of the FORK-256 hash function

We study the security of step-reduced but otherwise unmodified SHA-256. We show the first collision attacks on SHA-256 reduced to 23 and 24 steps with complexities 218 and 228.5, respectively. We give example colliding message pairs for 23-step and 24-step SHA-256. The best previous, recently obtained result was a collision attack for up to 22 steps. We extend our attacks to 23 and 24-step reduced SHA-512 with respective complexities of 244.9 and 253.0. Additionally, we show non-random behaviour of the SHA-256 compression function in the form of free-start near-collisions for up to 31 steps, which is 6 more steps than the recently obtained non-random behaviour in the form of a semi-free-start near-collision. Even though this represents a step forwards in terms of cryptanalytic techniques, the results do not threaten the security of applications using SHA-256.

https://lirias.kuleuven.be/bitstream/123456789/244806/2/article-1147.pdf

Florian Mendel

Papers

Cryptanalysis of Twister

Colliding message pair for 53-step HAS-160

A Distinguisher for the Compression Function of SIMD-512

Cryptanalysis of reduced variants of the FORK-256 hash function

Collisions and other Non-Random Properties for Step-Reduced SHA-256