As the most widely used technology to prevent eavesdropping on the Internet, HTTPS encryption has seen its share of attacks, most of which work by exploiting weaknesses that allow snoops to decode cryptographically scrambled traffic. Now there's a novel technique that can pluck out details as personal as someone's sexual orientation or a contemplation of suicide, even when the protection remains intact.
A recently published academic paper titled "I Know Why You Went to the Clinic: Risks and Realization of HTTPS Traffic Analysis" shows how even strongly encrypted Web traffic can reveal highly personal information to employers, Internet service providers, state-sponsored spies, or anyone else with the capability to monitor a connection between a site and the person visiting it. As a result, it's possible for them to know with a high degree of certainty what video someone accessed on Netflix or YouTube, the specific tax form or legal advice someone sought from an online lawyer service, and whether someone visiting the Mayo Clinic website is viewing pages related to pregnancy, headaches, cancer, or suicide.
The attack works by carefully analyzing encrypted traffic and taking note of subtle differences in data size and other characteristics of the encrypted contents. In much the way someone holding a wrapped birthday present can tell if it contains a book, a Blu-ray disk, or a box of candy, an attacker can know with a high degree of certainty the specific URL of the HTTPS-protected website. The transport layer security and secure sockets layer protocols underpinning the Web encryption specifically encrypt the URL, so until now, many people presumed an attacker could only deduce the IP address of a site someone was visiting rather than specific pages belonging to that site.