隨著科技的進步，人類的生活品質迎來前所未有的提升，而其中人們對於食品安全議題的重視程度亦日益增加。在台灣，自2011年爆發多起食安醜聞，舉國譁然之際，人民對於原有的食品履歷、食品標章、檢驗報告，以及政府對於食品把關的能力產生了不信任感。因此，如何在此不信任感之下建構一個可信賴的食品溯源系統成為本篇論文的主旨，而區塊鏈技術的特性正好可以消除對這些中心化第三方信任的依賴。
本篇論文針對之食品安全主要分為兩大面向。第一，食品的原物料來源之環境；第二，食品供應鏈所經過之物流配送環境。原物料來源環境方面以佈署於農場中的物聯網感測器所蒐集之精確環境數據，以及農場之多種檢驗報告書；而物流配送環境方面則同樣以物流車上配置之物聯網感測器所蒐集之數據。輔以區塊鏈技術，以其透明公開、去中心化等特性，為這些資料、數據在不信任之雙方下提供驗證。最後，我們的系統結合了電商功能，提供購物平台開放消費者直接於平台上購買這些經過來源驗證之食品，並提供食品之可信賴履歷之溯源。

With the advancement in technology, the quality of human life has ushered in an unprecedented improvement, and people are paying more and more attention to food safety issues. In Taiwan, the whole country was in an uproar when several food security scandals broke out in 2011. Since then, people increase the distrust of the resume, the certificates, and the testing reports of the food, as well as the government's functionality of monitoring the food safety. Therefore, constructing a reliable food traceability system under the distrust is the main purpose of this paper, and the characteristics of blockchain technology are happen to be able to eliminate the dependence on the trust of these centralized third-party.
In this thesis, we target on two aspects of food traceability: the environment in which the ingredients of the food are sourced, and the logistics and shipping environment through which the food supply chain passes. The source environment of the ingredients part is based on the accurate environmental data collected by the IoT sensors deployed at the farm, and the various certificates or testing report of the farms as well. As for the logistics shipping environment, is based on the data collected by the IoT sensor deployed in the vehicle. Supported by blockchain technology, with its characteristics, it provides verification for these data under the distrust of both parties. At last, our system supports e-commerce service. We provide a shopping platform for customers to purchase these source-proven foods, and the traceability of the trustworthy resume of the food as well.

Abstract -------------------------------------- I
中文摘要 -------------------------------------- II
Table of Contents --------------------------- III
List of Figures ------------------------------- V
List of Tables ------------------------------ VII
Chapter 1 Introduction ------------------------ 1
Chapter 2 Related Work ---------------------- 4
2.1 Blockchain -------------------------------- 4
2.1.1 Transactions and Mining ----------------- 5
2.1.2 Characteristics ------------------------- 6
2.1.3 Ethereum -------------------------------- 8
2.1.4 Private Chain --------------------------- 9
2.1.5 Smart Contract ------------------------- 10
2.1.6 Remix and Solidity --------------------- 10
2.2 IPFS ------------------------------------- 12
2.2.1 Overview ------------------------------- 12
2.2.2 Filecoin ------------------------------- 12
2.3 Food Traceability ------------------------ 14
Chapter 3 System Design ---------------------- 16
3.1 System Overview -------------------------- 16
3.2 User Scenarios --------------------------- 17
3.3 Back-end Server -------------------------- 18
3.3.1 Blockchain and Smart Contract Design --- 19
3.3.2 Database Design ------------------------ 23
3.3.3 API Design ----------------------------- 28
3.4 Traceability Service --------------------- 32
3.4.1 Overview ------------------------------- 32
3.4.1 Data Verification ---------------------- 33
Chapter 4 System Implementation -------------- 35
4.1 Data collecting -------------------------- 35
4.1.1 Node-cron ------------------------------ 35
4.1.2 Merkle Tree ---------------------------- 36
4.2 Smart Contract --------------------------- 38
4.2.1 Hash-storing Type Smart Contract ------- 38
4.2.2 Order Type Smart Contract -------------- 40
4.2.3 Transactions --------------------------- 43
4.3 API Server ------------------------------- 45
4.3.1 Node.js and Express -------------------- 45
4.3.2 Middleware ----------------------------- 46
4.3.3 MVC Pattern ---------------------------- 47
4.4 Traceability Service and Front-end APP --- 48
Chapter 5 Conclusion and Future Works -------- 56
References ----------------------------------- 58

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