You’ve probably heard about blockchain technology most often in the context of digital cryptocurrencies like Bitcoin, but the blockchain can be much more than that. In fact, the Defense Advanced Research Projects Agency (DARPA) is looking into an implementation of the blockchain that could fundamentally alter how sensitive military systems are secured. Blockchain technology could even help keep nuclear weapons safe and sound.

With Bitcoin, the blockchain is the universal record of all the transactions that take place. Although there are some ways to game the system in Bitcoin’s case, the blockchain is supposed to make sure bitcoins sent from one wallet to another are tracked and accounted for. That’s really all a blockchain is — a decentralized timeline of activity. Because of its distributed nature, it’s exceedingly difficult to modify data to hide activity, and that’s what makes blockchains so interesting in security. A centralized or distributed ledger is easier to hack.

Timothy Booher, who leads the DARPA blockchain efforts, describes the use of blockchains with the analogy of defending a castle. You can build walls higher and higher (i.e. network security measures), but people might still be able to find a way in no matter how well you think you sealed up all the cracks. It’s actually more important to know who has been inside the castle and what they did while inside the walls. A blockchain could log that sort of information, making it considerably harder to steal or modify files in a system.

In September, DARPA awarded a $1.8 million contract to a computer security firm to perform testing on a blockchain implementation provided by another contractor. This process is called “formal verification,” which means using mathematical processes to ensure code operates only in the intended fashion. It’s the closest thing to unhackable code, basically.

If the verification process goes well, DARPA could move to implement blockchain information integrity monitoring in high-security military systems, like those that control surveillance satellites or even nuclear weapons. This immutable record would be able to show if any files are changed or accessed with none of the guesswork that goes on now. Agencies and companies are often not even aware they’ve been hacked until their private data shows up for sale online.

Bitcoin and other cryptocurrencies have had their problems over the years, and none of the implementations are simple enough for average consumers to use in place of regular money. It’s still mostly used in illegal transactions and niche online purchases. So, maybe Bitcoin itself isn’t going to change the world, but the blockchain technology behind it could make it a lot safer.

Now read: What is the blockchain, and is it really about to change the world?