  Microblogging services such as Twitter are an increasingly important way to
communicate, both for individuals and for groups through the use of hashtags
that denote topics of conversation. However, groups can be easily blocked from
communicating through blocking of posts with the given hashtags. We propose
#h00t, a system for censorship resistant microblogging. #h00t presents an
interface that is much like Twitter, except that hashtags are replaced with
very short hashes (e.g., 24 bits) of the group identifier. Naturally, with such
short hashes, hashtags from different groups may collide and #h00t users will
actually seek to create collisions. By encrypting all posts with keys derived
from the group identifiers, #h00t client software can filter out other groups'
posts while making such filtering difficult for the adversary. In essence, by
leveraging collisions, groups can tunnel their posts in other groups' posts. A
censor could not block a given group without also blocking the other groups
with colliding hashtags. We evaluate the feasibility of #h00t through traces
collected from Twitter, showing that a single modern computer has enough
computational throughput to encrypt every tweet sent through Twitter in real
time. We also use these traces to analyze the bandwidth and anonymity tradeoffs
that would come with different variations on how group identifiers are encoded
and hashtags are selected to purposefully collide with one another.
