Mesh Network Rethink for Crowded Environments

A decentralized networking technology originally designed for battlefields and Burning Man is now being reimagined from the ground up.

Mesh networks, named for their fishnet-like connections, have emerged in recent decades as a result of rigorous mathematical research aimed at maintaining data flow even when parts of a system fail. But theory has not always matched reality. Real-world mesh networks have proven vulnerable to shutdowns in certain contexts, such as certain types of large crowds, which they are expected to be good at handling.

So researchers at Johns Hopkins University, Harvard, and the City College of New York recently built a prototype mesh network system that was hardened for some of the most challenging and conflict-ridden environments: political protests.

In a paper presented last week at the ACM Computer and Communications Security Conference in Taipei, researchers announced a prototype mesh network called Amigo. Amigo, for starters, was designed to work in environments where the internet was down, as was the case during the unrest in India, Iraq and Syria, among other countries.

“Cutting off the Internet during times of large civil protests is a way to prevent people from organizing and gathering,” says Tushar Jois, assistant professor of electrical engineering at City College. “This is why we are specifically adapting our technology.”

Amigo offers at least three ways to augment more traditional approaches to mesh networks. Recent studies of network outages in protest scenarios reveal problems such as network messages failing to be delivered, appearing out of order, and exposing users to tracking, even if network nodes (e.g. phones running the mail app) are right next to each other. The researchers found that digging into the mesh network’s high-level encrypted communications and basic Wi-Fi operations revealed opportunities that previous mesh networks had failed to capture.

“The story is that cryptography alone will not save us,” Jois explains. Jois and his colleagues presented a version of their Amigo paper earlier this year at the Real World Cryptography conference in Sofia, Bulgaria.

Why political protests matter in mesh networks

Amigo learned key lessons from a set of studies on mesh networking during a series of recent political protests, including pro-democracy actions in Hong Kong in 2019 and 2020.

For example, the way previous mesh networks handled the routing of their messages could accidentally lead to flooding of the area. Multiple nodes in a stressed network can send redundant messages across the network, slowing communications. In contrast, Amigo forms what researchers call dynamic “cliques,” in which only designated leader nodes exchange messages with each other, while regular nodes simply talk to their leader. According to the researchers, this technique significantly reduces message traffic, thereby reducing the risk of network blocking.

“We were among the people who discovered that in secure mesh messaging we had this blind spot,” Jois explains. “So we came up with new algorithms that help resolve this blind spot. Dynamic click-through routing essentially allows groups of nodes to self-organize routing units within a geographic area based on GPS.”

Another example is Amigo’s approach to cryptography and anonymity. Previous mesh environments provided no easy way to remove members from encrypted groups. (In a protest context, removing a group may be necessary, for example, because a device or its user has been apprehended by authorities.) Older mesh standards also leaked metadata that could reveal other members of the group. Amigo aims to fix both problems.

“One of the things we talk about is the anonymity of foreigners,” says Jois. “People outside your group don’t know the group exists. » Amigo, he says, is adding new algorithms to ensure third-party anonymity and group removal. Jois adds that Amigo aims to achieve these goals while retaining the protections of existing encrypted message networks like WhatsApp and Signal.

Traditionally, Jois adds, encrypted messaging offers a few important features. One of the features is to protect past messages: via “forward secrecy”, even if the keys are stolen today, past messages remain secure. The other involves protecting future messages: through “post-compromise security,” even a compromised system can heal by generating new keys and thereby preventing an intruder from accessing future communications. Amigo retains both features.

“We add [our new protections] to classic secrecy and post-compromise security,” says Jois. “But maybe we need more properties from a security perspective. So I think juggling all of that will be fun.

Diogo Baradas, an assistant professor of computer science at the University of Waterloo in Canada, adds that Amigo could find applications beyond political protests.

“Another scenario in which such crowd dynamics are particularly interesting includes natural disaster scenarios, such as floods, fires and earthquakes, where Internet communications could become unavailable,” says Baradas, who is not part of the Amigo team. “And concerned citizens, first responders and volunteers must coordinate to ensure an appropriate response. »

Developers built the Amigo mesh network around mathematical models of crowds based on studies of real-world crowds. Cora Ruiz

Today’s mesh networks know nothing about crowds

A final reality check for mesh standards emerges from a new study of how mesh networks manage crowds.

Cora Ruiz is a graduate student in the Jois Security, Privacy, and Cryptography Engineering Lab at City College. She studies the random walk approach to modeling crowds in most mesh networking environments.

Like nitrogen and oxygen molecules in an air sample, individual mesh nodes today are typically imagined to each trace random paths whose movements are uncorrelated to nearby nodes. If this, Ruiz says, is how mesh networks mathematically model crowd behavior, then no wonder Mesh networks seize up in some real-world environments.

“There’s really no understanding of how protesters physically move during these mass civil protests,” Ruiz says of traditional mesh models of crowd behavior. “And without that understanding of how people move and what drives movement, what it looks like at every level, it will be almost impossible to develop a truly bespoke solution.”

Instead, Ruiz is exploring ways to integrate models of what she calls psychological crowds into mesh network algorithms.

“Psychological crowds are a concentration of people in a place who share a certain sense of self,” she says. “And this sense of shared self can have a direct impact on how people move. They tend to move closer together. They don’t tolerate as much distance between them. They move more slowly.”

Jois says developing more realistic mathematical models of psychological crowds is an interdisciplinary effort. This is partly mathematics, partly sociology and group psychology. “[Ruiz’s] current work aims to determine the dynamics of communications and [group] dynamic by going to protest activists and journalists – in these places where Internet shutdowns are frequent – ​​and determining what their needs are,” he says.

“Since mesh is heavily influenced by physical movement and traffic patterns,” adds Ruiz, “having a solid understanding is essential to advancing Amigo and other future mesh messaging tools.”

Jois adds that Amigo took inspiration for its crowd models from a document created in 2019 by Hong Kong pro-democracy protesters, advising fellow activists how to march and rally. Building on this and other studies that could help design mathematical models of real-world crowd movements, Jois says Amigo represents an important next step toward bringing mesh networks into the real world.

“Our results show that fundamental work is needed in mesh networks,” says Jois. “We can stand up in our academic spaces and say, ‘Well, this is what we think is needed.’ But unless we get that from the source, we don’t know.