怎麼知道是否有人在用無人機在監視你呢?
這個研究是在你家裡,藉由電視或其他顯示裝置,產生特定的影像輪轉模式並加以顯示,以產生特定的視覺變化效果,然後藉由偵測並判讀所擷取的無線視訊串流中,是否含有相應的資料變化模式來判斷。
這是因為壓縮之影像會帶有key frame(基準)(完整的影像資料)以及delta frames(差異)(僅含其與基準影像間的差異資料),如果變化與顯示模式相同,即使該視訊串流是經過加密的(而無線傳輸一般不會用太厲害的資料加密方法,因為這樣就會太耗電,運算起來也太慢了,所以都只是將傳輸資料以簡單的亂碼來交換資料位置,然後每次傳輸歷程再更換一個亂碼而已,所以資料的疏密性還是會被保存),我們也就能知道視訊裡面有包含這個特定的影像模式,那你就知道有人在用無線傳輸的影像監視器(大部分是無人機)在看著你家了。
「The encrypted video streamed by a drone back to its operator is vulnerable to the same kind of analysis, the Ben Gurion researchers say. In their tests, they used a "smart film" to toggle the opacity of several panes of a house's windows while a DJI Mavic quadcopter watched it from the sky, changing the panes from opaque to transparent and back again in an on-off pattern. Then they showed that with just a parabolic antenna and a laptop, they could intercept the drone's radio signals to its operator and find that same pattern in the drone's encrypted data stream to show that the drone must have been looking at the house.」
A quirk of video compression lets spy targets see what the drone…