How India Censors the Web

TL;DR

This paper investigates the techniques Indian ISPs use for web censorship, revealing diverse methods and inconsistencies in blocked websites across different providers through robust testing methods.

Contribution

It introduces a suite of improved tests for detecting DNS, HTTP, and SNI-based censorship, and provides the largest known list of potentially blocked websites in India.

Findings

ISPs use varied censorship techniques

Different ISPs block different websites

SNI inspection is used for website blocking

Abstract

One of the primary ways in which India engages in online censorship is by ordering Internet Service Providers (ISPs) operating in its jurisdiction to block access to certain websites for its users. This paper reports the different techniques Indian ISPs are using to censor websites, and investigates whether website blocklists are consistent across ISPs. We propose a suite of tests that prove more robust than previous work in detecting DNS and HTTP based censorship. Our tests also discern the use of SNI inspection for blocking websites, which is previously undocumented in the Indian context. Using information from court orders, user reports, and public and leaked government orders, we compile the largest known list of potentially blocked websites in India. We pass this list to our tests and run them from connections of six different ISPs, which together serve more than 98% of Internet users in India. Our findings not only confirm that ISPs are using different techniques to block websites, but also demonstrate that different ISPs are not blocking the same websites.