This year researchers expect the world to snap（按快门）1.35 trillion photographs, or about 3.7 billion per day. All those pixels（像素）take up a lot of room if they are stored on personal computers or phones, which is one reason why many people store their images in the cloud. But unlike a hard on drive which can be encrypted（加密）to protect its data, cloud storage users have to trust that a tech platform will keep their private pictures safe. Now a team of Columbia University computer scientists has developed a tool to encrypt images stored on many popular cloud services while allowing authorized users to browse and display their photographs as usual.
Malicious（恶意的）attempts to access or leak cloud-based photographs can expose personal information. In November 2019, for example, a bug in the popular photograph storage app Google Photos mistakenly shared some users' private videos with strangers. Security experts also worry about employees at cloud storage companies on purpose accessing users' images.
So the Columbia researchers came up with a system called Easy Secure Photos（ESP）, which they presented at a recent conference. "We wanted to see if we could make it possible to encrypt data while using existing services," says computer scientist Jason Nieh, one of the developers of ESP. "Everyone wants to stay with Google Photos and not have to register on a new encrypted-image cloud storage service."
To overcome this problem, they created a tool that preserves blocks of pixels but moves them around to effectively hide the photograph. First, ESP's algorithm（算法）divides a photograph into three separate files, each one containing the image's red, green or blue color data. Then the system hides the pixel blocks around among these three files（allowing a block from the red file, for instance, to hide out in the green or blue ones）. But the program does nothing within the pixel blocks, where all the image processing happens. As a result, the files remain unchanged images but end up looking like grainy black-and-white ones to anyone who accesses them without the decryption key.