物聯網是最近很熱門的議題，吸引非常多研究的關注，具有十分廣闊的市場 前景。透過物聯網技術，現實世界的真實物體皆可連結上網，因而延伸出許多新 穎的應用，例如居家照護、智慧城市與智慧工廠等。隨著物聯網的應用越來越廣 泛，資料的安全性也顯得越益重要。尤有甚者，許多物聯網設備藉由無線電傳輸 來交換資料，攻擊者很容易可以擷取以無線電傳輸的資料封包，造成使用者資料 外洩。因此，如何使用密碼系統的加解密技術來確保私密資料的安全性，成為發 展物聯網的一個重要議題。現今的加解密技術可分為對稱式與非對稱式兩類。對 稱式技術在加密與解密時所使用的金鑰是相同的，而其計算成本是兩類技術中較 低的，但是金鑰的發佈與管理確較為困難。非對稱式技術使用一組相關連但是不 同的公鑰和私鑰進行加密與解密，其計算成本是兩類技術中較高的，但是公鑰可 以公開發佈，因此金鑰的發佈與管理確較為容易，而且可以利用公鑰做為數位簽 章之用。本研究改良Rabin 密碼系統的非對稱式加解密技術應用於物聯網，其做 法為隨機選定某個在固定已知範圍內的數值，並根據此數值重複明文的最後幾個 字節進行加密產生密文，如此可以防止Rabin 密碼系統遭受選擇密文攻擊。本研 究也利用Rabin 密碼系統在加密與解密計算成本也不對稱的特性，讓物聯網中計 算能力與記憶體空間有限制的設備使用成本較低的計算進行加解密，而其他資源 較充足的設備則使用成本較高的計算進行加解密，預期可以使物聯網具有隱私性 (privacy) 、完整性(integrity) 、不可否認(non-repudiation)及驗證識別 (Authentication)等特性。;In recent years, Internet of Things (IoT) has been a hot topic; it has attracted much research attention and has promising market prospects. IoT can be used to connect real world objects to the Internet, and thus creates novel applications, such as home care, smart cities, and smart factories. With the increasing adoption of IoT applications, the security of IoT data transmission is more and more important. Moreover, many IoT systems exchange data via wireless communications. Hackers are thus easy to intercept information to launch attacks. The encryption and decryption techniques of cryptosystems are applied to tackle the IoT security issues. The techniques are classified into two kinds: symmetric techniques and asymmetric techniques. Symmetric techniques use the same key to encrypt and decrypt data exchanged between devices. Asymmetric techniques use a pair of a public key and a private key to encrypt and decrypt data. Symmetric techniques have lower computation costs, but the distribution and management of keys are difficult for this kind of techniques. Asymmetric techniques have higher computation costs, but the public keys can be publicly distributed without leaking the system secrets. Moreover, they can be used to achieve digital signatures. This study is to improve the asymmetric Rabin cryptosystem for applying it to the IoT to resist the chosen ciphertext attack by duplicating the last few plaintext bytes of an arbitrary length that is within a fixed range. Moreover, this iii study utilizes the fact that the computation costs of encryption and decryption are also asymmetric in the Rabin cryptosystem. IoT devices with limited resources encrypt/decrypt data with lower computation, while devices with adequate resources encrypt/decrypt data with higher computation costs. The improved Rabin system is to endow the IoT with the properties of privacy, integrity, non-repudiation and authentication.
