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Oracle
yaohsin
https://medium.com/@yaohsin
2017-05-10
無限可能的Smart Contract
• 保險合約  汽車理賠
• 博弈  大樂透
• 交易所  ether換usd
• 預測市場  南韓總統大選誰勝出?
But…
封閉的EVM無法主動獲取來自真實世界的資料
所以會卡關
• 保險合約  汽車理賠  不知道汽車損傷程度
• 博弈  大樂透  不知道開獎結果
• 交易所  ether換usd  不知道即時匯率
• 預測市場  南韓總統大選誰勝出?  不知道…
怎麼辦?
這時就需要去找她
透過Oracle連接
區塊鏈世界與真實世界
Oracle種類
• human
• software
• Oraclize -> http://www.oraclize.it/
• Reality Keys -> https://www.realitykeys.com/
• GNOSIS -> https://gnosis.pm/
• hardware
• TREZOR
Oracle基本流程
Human Oracle
部署合約
發出Event
Human Oracle收到Event
Human Oracle送出Data
合約取回Data
Software Oracle
Oracle合約
• 架構中最重要的合約,負責接收query後傳送至
外界,並指定callback address確保只有自己能將
結果回傳
OracleResolver合約
• 當成Oracle合約與DAPP的中間層
• 可以彈性替換Oracle合約,而不影響DAPP
UsingMyOracle合約
• 提供給DAPP開發者使用的合約
• contract Dice is UsingMyOracle {
}
My Oracle程式
• software
• 監聽event
• 根據event內容自動callback回Dice合約
部署完成就可以擲骰子
But, 問題來了
• 我們可以信任Oracle嗎?
• 我們處理的是真金白銀
• 當利益夠大時,誰能保證Oracle不會動貪念
解法1:不只餵data還有Proof
Data + Proof
EVM
可驗證data來源正確,且沒被竄改
oraclize TLSNotary
https://tlsnotary.org/
總覺得哪裡怪怪的
EVM
球員兼裁判?
解法2:引用多個oracle
EVM
把Oracle當成sensor來使用
手續費將暴增?
問題2: 集中式Oracle
EVM
可能危害整個生態系統?
GNOSIS
https://gnosis.pm/
• Prediction Market as a Service
• 提供Decentralized Oracle
• 4/24剛完成ICO  $12.5M
• 採用 Oraclize, Reality Keys, etc.
Ultimate Oracle
有錢就可以任性?
終極解法或許長這樣?
EVM
Oracle chain
總結
• Oracle是區塊鏈跟現實世界的溝通管道
• 有Human, software, hardware三種形式
• 能傳送data與proof
• 市面上的Oracle服務
• 集中化:oraclize, Reality Keys
• 去中心化:GNOSIS
• 自己的data自己餵最安全?!
謝謝大家

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Oracle introduction