  This paper presents a study of the Internet infrastructure in India from the
point of view of censorship. First, we show that the current state of
affairs---where each ISP implements its own content filters (nominally as per a
governmental blacklist)---results in dramatic differences in the censorship
experienced by customers. In practice, a well-informed Indian citizen can
escape censorship through a judicious choice of service provider. We then
consider the question of whether India might potentially follow the Chinese
model and institute a single, government-controlled filter. This would not be
difficult, as the Indian Internet is quite centralized already. A few "key"
ASes (approx 1% of Indian ASes) collectively intercept approx 95% of paths to
the censored sites we sample in our study, and also to all publicly-visible DNS
servers. 5,000 routers spanning these key ASes would suffice to carry out IP or
DNS filtering for the entire country; approx 70% of these routers belong to
only two private ISPs. If the government is willing to employ more powerful
measures, such as an IP Prefix Hijacking attack, any one of several key ASes
can censor traffic for nearly all Indian users. Finally, we demonstrate that
such federated censorship by India would cause substantial collateral damage to
non-Indian ASes whose traffic passes through Indian cyberspace (which do not
legally come under Indian jurisdiction at all).
