Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2025/03/the-signal-chat-leak-and-the-nsa.html

US National Security Advisor Mike Waltz, who started the now-infamous group chat coordinating a US attack against the Yemen-based Houthis on March 15, is seemingly now suggesting that the secure messaging service Signal has security vulnerabilities.

"I didn’t see this loser in the group," Waltz told Fox News about Atlantic editor in chief Jeffrey Goldberg, whom Waltz invited to the chat. "Whether he did it deliberately or it happened in some other technical mean, is something we’re trying to figure out."

Waltz’s implication that Goldberg may have hacked his way in was followed by a report from CBS News that the US National Security Agency (NSA) had sent out a bulletin to its employees last month warning them about a security "vulnerability" identified in Signal.

The truth, however, is much more interesting. If Signal has vulnerabilities, then China, Russia, and other US adversaries suddenly have a new incentive to discover them. At the same time, the NSA urgently needs to find and fix any vulnerabilities quickly as it can—and similarly, ensure that commercial smartphones are free of backdoors—access points that allow people other than a smartphone’s user to bypass the usual security authentication methods to access the device’s contents.

That is essential for anyone who wants to keep their communications private, which should be all of us.

It’s common knowledge that the NSA’s mission is breaking into and eavesdropping on other countries’ networks. (During President George W. Bush’s administration, the NSA conducted warrantless taps into domestic communications as well—surveillance that several district courts ruled to be illegal before those decisions were later overturned by appeals courts. To this day, many legal experts maintain that the program violated federal privacy protections.) But the organization has a secondary, complementary responsibility: to protect US communications from others who want to spy on them. That is to say: While one part of the NSA is listening into foreign communications, another part is stopping foreigners from doing the same to Americans.

Those missions never contradicted during the Cold War, when allied and enemy communications were wholly separate. Today, though, everyone uses the same computers, the same software, and the same networks. That creates a tension.

When the NSA discovers a technological vulnerability in a service such as Signal (or buys one on the thriving clandestine vulnerability market), does it exploit it in secret, or reveal it so that it can be fixed? Since at least 2014, a US government interagency "equities" process has been used to decide whether it is in the national interest to take advantage of a particular security flaw, or to fix it. The trade-offs are often complicated and hard.

Waltz—along with Vice President J.D. Vance, Defense Secretary Pete Hegseth, and the other officials in the Signal group—have just made the trade-offs much tougher to resolve. Signal is both widely available and widely used. Smaller governments that can’t afford their own military-grade encryption use it. Journalists, human rights workers, persecuted minorities, dissidents, corporate executives, and criminals around the world use it. Many of these populations are of great interest to the NSA.

At the same time, as we have now discovered, the app is being used for operational US military traffic. So, what does the NSA do if it finds a security flaw in Signal?

Previously, it might have preferred to keep the flaw quiet and use it to listen to adversaries. Now, if the agency does that, it risks someone else finding the same vulnerability and using it against the US government. And if it was later disclosed that the NSA could have fixed the problem and didn’t, then the results might be catastrophic for the agency.

Smartphones present a similar trade-off. The biggest risk of eavesdropping on a Signal conversation comes from the individual phones that the app is running on. While it’s largely unclear whether the US officials involved had downloaded the app onto personal or government-issued phones—although Witkoff suggested on X that the program was on his "personal devices"—smartphones are consumer devices, not at all suitable for classified US government conversations. An entire industry of spyware companies sells capabilities to remotely hack smartphones for any country willing to pay. More capable countries have more sophisticated operations. Just last year, attacks that were later attributed to China attempted to access both President Donald Trump and Vance’s smartphones. Previously, the FBI—as well as law enforcement agencies in other countries—have pressured both Apple and Google to add "backdoors" in their phones to more easily facilitate court-authorized eavesdropping.

These backdoors would create, of course, another vulnerability to be exploited. A separate attack from China last year accessed a similar capability built into US telecommunications networks.

The vulnerabilities equities have swung against weakened smartphone security and toward protecting the devices that senior government officials now use to discuss military secrets. That also means that they have swung against the US government hoarding Signal vulnerabilities—and toward full disclosure.

This is plausibly good news for Americans who want to talk among themselves without having anyone, government or otherwise, listen in. We don’t know what pressure the Trump administration is using to make intelligence services fall into line, but it isn’t crazy to worry that the NSA might again start monitoring domestic communications.

Because of the Signal chat leak, it’s less likely that they’ll use vulnerabilities in Signal to do that. Equally, bad actors such as drug cartels may also feel safer using Signal. Their security against the US government lies in the fact that the US government shares their vulnerabilities. No one wants their secrets exposed.

I have long advocated for a "defense dominant" cybersecurity strategy. As long as smartphones are in the pocket of every government official, police officer, judge, CEO, and nuclear power plant operator—and now that they are being used for what the White House now calls calls  "sensitive," if not outright classified conversations among cabinet members—we need them to be as secure as possible. And that means no government-mandated backdoors.

We may find out more about how officials—including the vice president of the United States—came to be using Signal on what seem to be consumer-grade smartphones, in a apparent breach of the laws on government records. It’s unlikely that they really thought through the consequences of their actions.

Nonetheless, those consequences are real. Other governments, possibly including US allies, will now have much more incentive to break Signal’s security than they did in the past, and more incentive to hack US government smartphones than they did before March 24.

For just the same reason, the US government has urgent incentives to protect them.

This essay was originally published in Foreign Policy.