Blockchain technology has been slow to gain adoption in non-financial contexts, but it could turn out to have invaluable military applications. DARPA, the storied research unit of the US Department of Defense, is currently funding efforts to find out if blockchains could help secure highly sensitive data, with potential applications for everything from nuclear weapons to military satellites.

The case for using a blockchain boils down to a concept in computer security known as “information integrity.” That’s basically being able to track when a system or piece of data has been viewed or modified. DARPA’s program manager behind the blockchain effort, Timothy Booher, offers this analogy: Instead of trying to make the walls of a castle as tall as possible to prevent an intruder from getting in, it’s more important to know if anyone has been inside the castle, and what they’re doing there.

A blockchain is a decentralized, immutable ledger. Blockchains can permanently log modifications to a network or database, preventing intruders from covering their tracks. In DARPA’s case, blockchain tech could offer crucial intelligence on whether a hacker has modified something in a database, or whether they’re surveilling a particular military system.

“Whenever weapons are employed … it tends to be a place where data integrity in general is incredibly important,” Booher says. “So nuclear command and control, satellite command and control, command and control in general, [information integrity] is very important.”

This September, DARPA, which stands for Defense Advanced Research Projects Agency (the agency helped create the internet, among other things), awarded a $1.8 million contract to a computer security firm called Galois. The firm’s assignment is to formally verify—a sort of computer-code audit, using mathematics—a particular type of blockchain tech supplied by a company called Guardtime. Formal verification is one way to build nearly unhackable code, and it’s a big part of DARPA’s approach to security.

If the verification goes well, it would inch DARPA closer to using some form of blockchain technology for the military, Booher says. “We’re certainly thinking through a lot of applications,” he says. “As Galois does its verification work and we understand at a deep level the security properties of this [technology] then I would start to set up a series of meetings [with the rest of the agency] to start that dialog.”

The prospect of the US military using a blockchain to secure critical data could spark a boom in uses of the technology outside finance. Investors poured $134 million into blockchain startups in the first quarter of 2016, according to research by trade publication CoinDesk. These firms have focused overwhelmingly on financial applications to date. But information security represents a huge new market for blockchain tech vendors, accounting for $75 billion in spending last year, and projected to hit $108 billion in 2019, according to forecasts by market research firm Gartner.

In an age of mega-hacks on corporations and political organizations, an indelible record that detects tampering has its attractions. “We want to provide an extremely high level of trust … what this work is after is the highest level possible,” Booher says, “If someone is driving a combat vehicle, flying an aircraft, commanding a satellite, we want to make sure their focus is 100% on that mission.”