Single-Use Delegatable Signatures Based on Smart Contracts

TL;DR

This paper introduces a blockchain-based method for delegatable signatures that allows users to set usage limits, ensuring controlled signing rights without specialized hardware, demonstrated through Ethereum implementations.

Contribution

It proposes a novel smart contract-based approach to enforce usage limits on delegated signatures, overcoming limitations of existing solutions.

Findings

Efficient implementation of threshold-based signing limits on Ethereum.

Proof of concept demonstrating real-world feasibility.

Enhanced control over delegated signing rights.

Abstract

Delegation of cryptographic signing rights has found many application in the literature and the real world. However, despite very advanced functionalities and specific use cases, existing solutions share the natural limitation that the number of usages of these signing rights cannot be efficiently limited, but users can at most be disincentivized to abuse their rights. In this paper, we suggest a solution to this problem based on blockchains. We let a user define a smart contract defining delegated signing rights, which needs to be triggered to successfully sign a message. By leveraging the immutability of the blockchain, our construction can now guarantee that a user-defined threshold of signature invocations cannot be exceeded, thereby circumventing the need for dedicated hardware or similar assistance in existing constructions for one-time programs. We discuss different constructions supporting different features, and provide concrete implementations in the Solidity language of the Ethereum blockchain, proving the real-world efficiency and feasibility of our construction.