A constrained Hamiltonian formulation of supergravity

Thesis--University of Tsukuba, D.Sc.(A), no. 95, 1981. 3. 2

Crystal structure of an acetylesterase from Talaromyces cellulolyticus and the importance of a disulfide bond near the active site

AbstractCarbohydrate esterase catalyzes the de-O or de-N-acylation of substituted saccharides in plant cell walls and thus has great potential for industrial biomass saccharification. We recently identified the putative carbohydrate esterase family 3 (CE3) from Talaromyces cellulolyticus. Here, we prepared the recombinant catalytic domain of the enzyme and crystallized it. The crystal structure was determined to 1.5Å resolution. From the structural analysis, it was elucidated that a n-octyl-β-d-glucopyranoside bound to near the catalytic triad (Ser10, Asp179 and His182) and was buried in the active site cavity. Site-directed mutagenesis showed that the N-terminal disulfide bond located near the catalytic triad is involved in the activity and structural stability of the enzyme

Cryptanalysis of OCB2

We present practical attacks against OCB2, an ISO-standard authenticated encryption (AE) scheme. OCB2 is a highly-efficient blockcipher mode of operation. It has been extensively studied and widely believed to be secure thanks to the provable security proofs. Our attacks allow the adversary to create forgeries with single encryption query of almost-known plaintext. This attack can be further extended to powerful almost-universal and universal forgeries using more queries. The source of our attacks is the way OCB2 implements AE using a tweakable blockcipher, called XEX*. We have verified our attacks using a reference code of OCB2. Our attacks do not break the privacy of OCB2, and are not applicable to the others, including OCB1 and OCB3

GIFT-COFB is Tightly Birthday Secure with Encryption Queries

GIFT-COFB is a finalist of NIST Lightweight cryptography project that aims at standardizing authenticated encryption schemes for constrained devices. It is a block cipher-based scheme and comes with a provable security result. This paper studies the tightness of the provable security bounds of GIFT-COFB, which roughly tells that, if instantiated by a secure $n$-bit block cipher, we need $2^{n/2}$ encrypted blocks or $2^{n/2}/n$ decryption queries to break the scheme. This paper shows that the former condition is indeed tight, by presenting forgery attacks that work with $2^{n/2}$ encrypted blocks with single decryption query. This fills the missing spot of previous attacks presented by Khairallah, and confirms the tightness of the security bounds with respect to encryption. We remark that our attacks work independent of the underlying block cipher

Parallelizable Authenticated Encryption with Small State Size

Authenticated encryption (AE) is a symmetric-key encryption function that provides confidentiality and authenticity of a message. One of the evaluation criteria for AE is state size, which is memory size needed for encryption. State size is especially important when cryptosystem is implemented in constrained devices, while trivial reduction by using a small primitive is not generally acceptable as it leads to a degraded security. In these days, the state size of AE has been very actively studied and a number of small-state AE schemes have been proposed, but they are inherently serial. It would be a natural question if we come up with a parallelizable AE with a smaller state size than the state-of-the-art. In this paper, we study the seminal OCB mode for parallelizable AE and propose a method to reduce its state size without losing the bit security of it. More precisely, while (the most small-state variant of) OCB has $3n$-bit state, by carefully treating the checksum that is halved, we can achieve $2.5n$-bit state, while keeping the $n/2$-bit security as original. We also propose an inverse-free variant of it based on OTR. While the original OTR has $4n$-bit state, ours has $3.5n$-bit state. To our knowledge these numbers are the smallest ones achieved by the blockcipher modes for parallel AE and inverse-free parallel AE

Requirements of basic amino acid residues within the lectin-like domain of LOX-1 for the binding of oxidized low-density lipoprotein

AbstractLectin-like OxLDL receptor-1 (LOX-1) was identified as the major receptor for oxidized low-density lipoprotein (OxLDL) in aortic endothelial cells. LOX-1 is a type II membrane protein that structurally belongs to the C-type lectin family. Here, we found that the lectin-like domain of LOX-1 is essential for ligand binding, but the neck domain is not. In particular, the large loop between the third and fourth cysteine of the lectin-like domain plays a critical role for OxLDL binding as well as C-terminal end residues. Alanine-directed mutagenesis of the basic amino acid residues around this region revealed that all of the basic residues are involved in OxLDL binding. Simultaneous mutations of these basic residues almost abolished the OxLDL-binding activity of LOX-1. Electrostatic interaction between basic residues in the lectin-like domain of LOX-1 and negatively charged OxLDL is critical for the binding activity of LOX-1