⾼度化する暗号技術と数学的技法の進展
Advances in Sophisticated Cryptography and Mathematical Techniques

アブストラクト
11/7
⾯ 和成（筑波⼤学）
Title：Blockchain and its applied research
Abstract： Blockchain is a secure distributed ledger system built with digital

signatures and cryptographic hash functions that satisfies both tamper resistanceand high availability. Blockchain emerged with cryptoassets and is now applied invarious fields where data falsification or system crash is critical, such as finance,
supply chain, and medical information. In addition, blockchain has a feature thatallows programs called "smart contracts" to run by themselves, which opens a wide
range of application possibilities. In this talk, I will explain about cryptoassets,blockchain, and smart contracts, and introduce recent applied research on
notarization system using individual number card and smart contracts.
吉野 雅之/⼭本 恭平（⽇⽴製作所）
Title：On research of cryptography for secure SaaS: attacks, security requirements

and practical solutions
Abstract：The Corona disaster in the 2020s triggered a shift to teleworking in just a
few years. SaaS, which allows workers to use a computing environment from homeequivalent to the workplace, has become increasingly popular. While the use ofdata has increased, data management has not been strengthened, and the scale ofdata leaks has grown over the years. Recent research on multi-party computationand homomorphic encryption has not matured to provide secure SaaS to generalusers. This presentation will discuss the challenges of realizing secure SaaS andintroduce the proposed methods using multiple cryptographic techniques (SSE,TEE, and HE).
髙橋 朋伽（⼤阪⼤学）
Title：On the Weakness of Ring-LWE mod Prime ideal by Trace MapAbstract ： The recent decision by the National Institute of Standards andTechnology (NIST) to standardize lattice-based cryptography has further
increased the demand for security analysis of it. The Ring-Learning with Error(Ring-LWE) problem is one of the mathematical problems that constitute suchlattice cryptography, and it has many algebraic properties because it is consideredin the ring of integers R of an algebraic number field K. These algebraic properties

make the Ring LWE based schemes efficient, while some of them are also used forattacks. When the modulus q is unramified in K, it is known that the Ring-LWE
problem, to determine the secret information s in R/qR, can be solved bydetermining s (mod p) for all prime ideals p lying over q. The χ2-attack
determines s (mod p) by using the χ2-test over a finite field Fq^f, which is
improved in the special case where the residue degree f is two, called thetwo-residue-degree χ2-attack. We extend the two-residue-degree χ2-attack to
the prime-residue-degree and composite-number-residue-degree χ2-attack. Our
extensions enable the χ2-attack to not only two but also any residue-degree casemore efficiently work. As a result, the attack time against a vulnerable field to our
proposed attacks with parameter (q,f)=(67,3) took 129 seconds on a standard PC.

11/8
清藤 武暢（有限責任監査法⼈トーマツ）
Title：Recent Trends on Zero-Knowledge Proof: Theory and its Applications
Abstract：Recently, studies are underway in various fields of organizations toimprove internal operations and generate new business values by using data
sharing and/or usage platforms. Organizations are focused on privacy-enhancing
technologies to guarantee the security of data handled on the above platforms(PETs, for short). And, the zero-knowledge proof is one of the main technology ofPETs. This technology can achieve a mechanism that a third party can verify that
attributes of data are correct without sharing actual data. In this talk, we will
overview the theory and some use cases of the zero-knowledge proof.

松岡 航太郎（京都⼤学）
Title：Evaluating Boolean circuits over ciphertexts using Fully

Homomorphic Encryption over the Torus
Abstract ： In this talk, I will explain how to evaluate Boolean circuits overciphertexts using Fully Homomorphic Encryption over the Torus (TFHE). By
representing privacy-preserving computing as Boolean circuits, we can use
conventional logic synthesis tools. TFHE is suitable for the Boolean circuit
evaluations because it supports fast Bootstrapping, the heaviest part for deep
circuits evaluations. This talk aims to tell how to construct the secure boolean
circuit evaluation method from basic mathematics to some technicalconsiderations for performance and security.

⼩貫 啓史（東京⼤学）
Title：Recent topics for isogeny-based cryptography
Abstract ： Recently, a series of researches gave serious attacks to SIKE, anisogeny-based protocol that is one of the NIST PQC candidates. These attacks
highly depend on the design of SIKE, and there are other isogeny-based protocols
which are considered to be secure against these attacks. I will give an overview ofthe attacks to SIKE and show which protocols are still considered to be secure.
渡邉 洋平（電気通信⼤学）
Title：Recent Progress in Searchable Encryption
Abstract：Consider a two-party information retrieval system where a server stores adatabase and a client sends the server queries to search the database for thequeries. Searchable encryption enables the client to search for a keyword, even if
the database is encrypted, without revealing any useful information on thedatabase to the server. In this talk, I focus on searchable symmetric encryption(SSE), one of the active research areas on searchable encryption. I will provide thehistorical background of SSE research, discuss trade-offs between security levels
and efficiency in SSE, and show the state-of-the-art SSE schemes.

11/9
安⽥ 貴徳（岡⼭理科⼤学）
Title：Construction of pairing using elliptic curvesAbstract：A practical pairing requires small embedding degrees. It imposes strong

conditions for the orders of elliptic curves, and the CM theory is indispensable.
Recently, pairing is applied to the zk-SNARKs, which require additional
conditions for the elliptic curves from the view of efficiency. Consequently, usable
curves for the zk-SNARKs are limited. The construction of a good pairing is even
now a problem.
Dung Hoang Duong（University of Wollongong）
Title：Cryptography from group actions
Abstract： Cryptographic Group Actions have been taken a lot of attentions

recently, especially in the context of isogeny-based cryptography. In this talk, I will
introduce another new research direction on non-commutative cryptographic
group actions and their interconnections with other areas of cryptography. I will
also introduce some possible cryptographic constructions.