Delight @ Keio SFC-RG

In this paper, we propose a conceptual model for claim validation based on signed data while clarifying the gap between validation and verification. As various activities are conducted via the Internet and the Web, verifying information and its originators is essential for countermeasures against threats, such as spoofing or falsifying an achievement. These discussions utilize cryptographically signed data, which includes a digital signature that allows a recipient can confirm the authenticity of the source using cryptographic techniques. In applications that utilize signed data to represent a claim, the recipient judges whether the claim is valid to avoid misidentification of the claim. However, the standards for digital certificates, such as Verifiable Credentials, do not cover the validation of the claim represented by the certificate, including the truth or falsity of the claim. Considering that verifying a signature does not directly indicate the validity of the claim, the gap between verification and validation should be clarified to cover the validation of the claim. We then hypothesize that the gap is the presence or absence of the validator’s criteria, and review the definitions in two standard documents to confirm our hypothesis. We then propose a conceptual model for claim validation that utilizes signed data. In our model, a validator, who is a recipient of the claim, defines a validation policy to represent the validator’s criteria. We also discuss a communication model between the claimant, who is a originator of the claim, and the validator. For claims that the validator cannot directly validate, we introduce an additional model that involves a certifier that the validator trusts. We analyze the applicability of our model through three use cases, and conclude that our models are applicable. Based on our model, we anticipate exploring several scenarios to validate diverse claims using signed data.

In this paper, to estimate the risk of economic loss incurred by both parties in production order transactions, we propose a scheme that enables escrow and confirmation of the results without relying on a third party. In such transactions, both parties risk incurring economic losses if the other party behaves dishonestly. Generally, the risk can be reduced with an escrow service provided by a trusted third party. However, there is a risk of fraud by the third party; in some cases, the third party may not be available for the buyer or seller. Several existing schemes utilize fair exchange and blockchain to disburse the deposited payment upon the delivery of specific data. However, in production order transactions, some cases cannot be handled only by completion of delivery, such as disputes that arise when the data does not meet the quality expected by the buyer. In such cases, before the transaction starts, a party would confirm the counterparty’s behavior in past transactions to estimate the risk of a dispute occurring. In this paper, we propose a scheme that records the history of past transaction processes while utilizing blockchain-based escrow and allows future counterparties to confirm the history as a reference for estimating risk. By the opportunity loss that a history of dishonest behavior causes and applying blockchain-based escrow, the scheme motivates sellers and buyers to behave in good faith. We implemented a prototype system on top of Ethereum and verified its feasibility. By expanding the scope of transactions, we expect that it will be possible to determine whether transactions between individuals over the Internet are feasible without relying on a specific escrow service.

To receive effective treatment during emergency response due to seizures or unforeseen accidents, a patient with intractable diseases must disclose information about their disease to an emergency physician. If the patient loses consciousness while traveling, the patient should disclose this information to a companion in advance. However, disclosing this information to a companion is undesirable because the information is confidential. Thus, we propose a system that discloses specific information on intractable diseases only when an emergency physician has verified they possess a medical license. Otherwise, the proposed system only discloses appropriate first aid information. We implemented a prototype of the proposed under the assumption that a physician has a digital medical license based on verifiable credentials (i.e., a standard for digital credentials). With this system, the patient does not disclose confidential information to the patient’s companion but does disclose necessary information to the emergency physician.

Transaction processing capacity limits the utility of Ethereum, one of the most well-known blockchain mainly used as a decentralized application. To enable more diverse applications, it is required to raise the transaction-per-seconds(TPS) limitation to lower transaction costs without compromising security as much as possible. To achieve this, several types of research are ongoing. One of the most extensive areas is called “Layer 2.” Layer 2 executes transactions externally on the blockchain, also called Layer 1, and the blockchain secures the correctness of transactions on Layer 2. A major Layer 2 method on Ethereum called “Rollup” is currently in use. Rollup is a mechanism that periodically summarizes Rollup transactions as a batch and writes them to Layer 1, such as Ethereum. A proof system deployed on Layer 1 guarantees the correctness of the result of the Rollup transaction execution. However, writing all Layer 2 transactions to Layer 1 and verifying the proof on Layer 1 still need a certain amount of Gas. Gas represents the amount of computation and storage required to run the program on Ethereum. Since Ethereum fee is Gas mount*Gas Price (Market Value), reducing Gas amount will also lead to a reduction in transaction fees. In this paper, we propose a new scheme called “Rollup on Rollup” to improve the Gas amount efficiency of executing transactions without compromising Layer 1 security. In this scheme, a Rollup operator is writing and verifying transactions on rollup, not on Layer 1, to reduce Gas for the verification. This scheme will allow us to execute transactions cheaper even with a higher transaction processing demand.