使用偏振光之短距離安全通訊系統

Abstract

本論文呈獻使用偏振光之短距離安全通訊系統—LightLock。由於偏振光之偏振狀態在反射後就幾乎被破壞，因此本系統能夠有效限縮具備直射性之傳送端及接收端通訊中可能被竊聽並竄改訊號之範圍。此外，LightLock 要求使用者必須額外旋轉出角度金鑰，以此作為輔助且獨立於數位金鑰之驗證因素，這提供了額外的安全性。我們以市場現成的元件實作 LightLock，包括感光二極體、線性偏振片以及液晶元件。實驗結果顯示，由於反射後的偏振光不再維持經偏振調變之原偏振性，可接收資料之距離被限縮到 7 公分且入射角必須在 30◦以內才能成功解碼。經實際使用者測試，使用者使用此具備雙因素驗證之系統僅有 4.76 % 的失誤率。

In this work, we propose LightLock, a short-range secure communication system leveraging polarized light. The polarization state of a polarized light wave is mostly destroyed after reflected off a surface. As a result, our system limits the possible locations for attacks such as eavesdropping and falsified transmission to those with a line-of-sight path to the transmitter or the receiver. In addition to support secure transmission of a key sequence, as a second and independent factor for authentication, LightLock also requires the user to rotate the device according to an authenticating angle sequence, providing added security. We implemented LightLock with off-the-shelf components, including LED, linear polarizers, and a liquid crystal cell. Evaluation results show that successful reception of data is limited to a short distance of 7 cm and incidence angle within 30◦ in line-of-sight scenario, while reflected transmission no longer maintain the modulated polarization states for successful demodulation. The user study shows that a user can successfully perform the two-factor authentication with a low 4.76% failure rate.