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

The Internet of Things vision: Key features, applications and open issues

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

An Introduction to Probability Theory and its Applications, Volume I

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

RFID security is currently one of the major challenges cryptography has to face, often solved by protocols assuming that an ontag hash function is available. In this article we present the PHOTON lightweight hash-function family, available in many different flavors and suitable for extremely constrained devices such as passive RFID tags. Our proposal uses a sponge-like construction as domain extension algorithm and an AES-like primitive as internal unkeyed permutation. This allows us to obtain the most compact hash function known so far (about 1120 GE for 64-bit collision resistance security), reaching areas very close to the theoretical optimum (derived from the minimal internal state memory size). Moreover, the speed achieved by PHOTON also compares quite favorably to its competitors. This is mostly due to the fact that unlike for previously proposed schemes, our proposal is very simple to analyze and one can derive tight AES-like bounds on the number of active Sboxes. This kind of AES-like primitive is usually not well suited for ultra constrained environments, but we describe in this paper a new method for generating the column mixing layer in a serial way, lowering drastically the area required. Finally, we slightly extend the sponge framework in order to offer interesting trade-offs between speed and preimage security for small messages, the classical use-case in hardware.

/pdf/the-photon-family-of-lightweight-hash-functions-3uam81b18v.pdf

The PHOTON family of lightweight Hash functions

In this paper, we present preimage attacks on up to 43-step SHA-256 (around 67% of the total 64 steps) and 46-step SHA-512 (around 57.5% of the total 80 steps), which significantly increases the number of attacked steps compared to the best previously published preimage attack working for 24 steps. The time complexities are 2251.9, 2509 for finding pseudo-preimages and 2254.9, 2511.5 compression function operations for full preimages. The memory requirements are modest, around 26 words for 43-step SHA-256 and 46-step SHA-512. The pseudo-preimage attack also applies to 43-step SHA-224 and SHA-384. Our attack is a meet-in-the-middle attack that uses a range of novel techniques to split the function into two independent parts that can be computed separately and then matched in a birthday-style phase.

/pdf/preimages-for-step-reduced-sha-2-qt856a4iog.pdf

Preimages for Step-Reduced SHA-2

We revisit narrow-pipe designs that are in practical use, and their security against preimage attacks. Our results are the best known preimage attacks on Tiger, MD4, and reduced SHA-2, with the result on Tiger being the first cryptanalytic shortcut attack on the full hash function. Our attacks runs in time 2188.8 for finding preimages, and 2188.2 for second-preimages. Both have memory requirement of order 28, which is much less than in any other recent preimage attacks on reduced Tiger. Using pre-computation techniques, the time complexity for finding a new preimage or second-preimage for MD4 can now be as low as 278.4 and 269.4 MD4 computations, respectively. The second-preimage attack works for all messages longer than 2 blocks.

/pdf/advanced-meet-in-the-middle-preimage-attacks-first-results-30kjo3y7xq.pdf

Advanced Meet-in-the-Middle Preimage Attacks: First Results on Full Tiger, and Improved Results on MD4 and SHA-2

This paper presents ongoing work towards extensions of meet-in-the-middle (MITM) attacks on block ciphers. Exploring developments in MITM attacks in hash analysis such as: (i) the splice-and-cut technique; (ii) the indirect-partial-matching technique. Our first contribution is that we show corrections to previous cryptanalysis and point out that the key schedule is more vulnerable to MITM attacks than previously reported. Secondly we further improve the time complexities of previous attacks with (i) and (ii), now the 80-bit secret key of the full rounds KTANTAN-{32,48,64} can be recovered at time complexity of 272.9, 273.8 and 274.4 respectively, each requiring 4 chosen-plaintexts.

/pdf/improved-meet-in-the-middle-cryptanalysis-of-ktantan-poster-g3wv192wo9.pdf

Jian Guo

Papers

The LED block cipher

The PHOTON family of lightweight Hash functions

Preimages for Step-Reduced SHA-2

Advanced Meet-in-the-Middle Preimage Attacks: First Results on Full Tiger, and Improved Results on MD4 and SHA-2

Improved Meet-in-the-Middle cryptanalysis of KTANTAN (poster)