適應於NuCypher之代理門檻廣播重加密機制

近幾年隨著區塊鏈技術的蓬勃發展，誕生了許多基於區塊鏈及智能合約(Smart Contract) 的新型應用，特別是以去中心化為核心價值的DApps(Decentralized Application) 應用。其中於2020 年正式上線的 NuCypher，旨在公鏈(Main Net) 上提供以密碼學基礎工程打造資料隱私保護(privacy preserving) 的服務，主要籍由智能合約的管控及密碼學中的重加密技術，達到在去中心化的環境中，依然能提供安全的資料分享應用。然而，在NuCypher 的機制中，對於資料的授權，只能提供一對一的分享服務，無法在同一時間，允許多位使用者存取同一份加密資料，而需個別設定，欠缺實務上的彈性及效率。所以本研究的重點在於改善其重加密機制以達成一對多分享的效果，使用代理廣播重加密(Proxy Broadcast ReEncryption PBRE) 演算法及祕密分享(Secret Sharing)技術，提出一個新機制來實現此一目標，除了達成原本NuCypher 隱私資料分享的特性，也依然保留了適合去中心化架構下的分散式儲存金鑰安全性。

關鍵字

NuCypher ；祕密分享；公鑰廣播加密；廣播重加密；區塊鏈

並列摘要

There are a bunch of applications based on Blockchain and Smart Contractlargely grow in recent years, especially, the development of DApps(DecentralizedApplications) based on the decentralized concept. One of many interestingBlockchain applications is NuCypher that focuses on providing securelyprivacypreservingservices. The NuCypher leverages the ReEncryptionmechanismand Smart Contract to build the datasharingsystem where runs underthe decentralized environment. As our observation, unfortunately, the NuCypher can just share the data1on1at the same time, it can not allow the data owner to share 1toN.Inthis case, It needs to set one by one so that it is inefficient and inflexible. So,our research focuses on enhancing the NuCypher cryptographic scheme toachieve 1toNsharing. We make use of the Proxy Broadcast ReEncryption(PBRE) algorithm and Secret Sharing scheme to propose our scheme. It doesnot only preserves the sharing feature as the NuCypher but also suitable fordecentralized environment to keep the distributed secure key management.Keywords: NuCypher, Secret Sharing, Broadcast Encrytion, Proxy BroadcastReEncryption,Blockchain.