As I write this in March 2025, there is a lot of confusion about Signal messenger due to the recent news of people using Signal in government, and subsequent leaks.

The short version is: there was no problem with Signal here. People were using it because they understood it to be secure, not the other way around.

Both the government and the Electronic Frontier Foundation recommend people use Signal. This is an unusual alliance, and in the case of the government, was prompted because it understood other countries had a persistent attack against American telephone companies and SMS traffic.

So let’s dive in. I’ll cover some basics of what security is, what happened in this situation, and why Signal is a good idea.

This post isn’t for programmers that work with cryptography every day. Rather, I hope it can make some of these concepts accessible to everyone else.

What makes communications secure?

When most people are talking about secure communications, they mean some combination of these properties:

1. Privacy - nobody except the intended recipient can decode a message.
2. Authentication - guarantees that the person you are chatting with really is the intended recipient.
3. Ephemerality - preventing a record of the communication from being stored. That is, making it more like a conversation around the table than a written email.
4. Anonymity - keeping your set of contacts to yourself and even obfuscating the fact that communications are occurring.

If you think about it, most people care the most about the first two. In fact, authentication is a key part of privacy. There is an attack known as man in the middle in which somebody pretends to be the intended recipient. The interceptor reads the messages, and then passes them on to the real intended recipient. So we can’t really have privacy without authentication.

I’ll have more to say about these later. For now, let’s discuss attack scenarios.

What compromises security?

There are a number of ways that security can be compromised. Let’s think through some of them:

Communications infrastructure snooping

Let’s say you used no encryption at all, and connected to public WiFi in a coffee shop to send your message. Who all could potentially see it?

• The owner of the coffee shop’s WiFi
• The coffee shop’s Internet provider
• The recipient’s Internet provider
• Any Internet providers along the network between the sender and the recipient
• Any government or institution that can compel any of the above to hand over copies of the traffic
• Any hackers that compromise any of the above systems

Back in the early days of the Internet, most traffic had no encryption. People were careful about putting their credit cards into webpages and emails because they knew it was easy to intercept them. We have been on a decades-long evolution towards more pervasive encryption, which is a good thing.

Text messages (SMS) follow a similar path to the above scenario, and are unencrypted. We know that all of the above are ways people’s texts can be compromised; for instance, governments can issue search warrants to obtain copies of texts, and China is believed to have a persistent hack into western telcos. SMS fails all four of our attributes of secure communication above (privacy, authentication, ephemerality, and anonymity).

Also, think about what information is collected from SMS and by who. Texts you send could be retained in your phone, the recipient’s phone, your phone company, their phone company, and so forth. They might also live in cloud backups of your devices. You only have control over your own phone’s retention.

So defenses against this involve things like:

• Strong end-to-end encryption, so no intermediate party – even the people that make the app – can snoop on it.
• Using strong authentication of your peers
• Taking steps to prevent even app developers from being able to see your contact list or communication history

You may see some other apps saying they use strong encryption or use the Signal protocol. But while they may do that for some or all of your message content, they may still upload your contact list, history, location, etc. to a central location where it is still vulnerable to these kinds of attacks.

When you think about anonymity, think about it like this: if you send a letter to a friend every week, every postal carrier that transports it – even if they never open it or attempt to peak inside – will be able to read the envelope and know that you communicate on a certain schedule with that friend. The same can be said of SMS, email, or most encrypted chat operators. Signal’s design prevents it from retaining even this information, though nation-states or ISPs might still be able to notice patterns (every time you send something via Signal, your contact receives something from Signal a few milliseconds later). It is very difficult to provide perfect anonymity from well-funded adversaries, even if you can provide very good privacy.

Device compromise

Let’s say you use an app with strong end-to-end encryption. This takes away some of the easiest ways someone could get to your messages. But it doesn’t take away all of them.

What if somebody stole your phone? Perhaps the phone has a password, but if an attacker pulled out the storage unit, could they access your messages without a password? Or maybe they somehow trick or compel you into revealing your password. Now what?

An even simpler attack doesn’t require them to steal your device at all. All they need is a few minutes with it to steal your SIM card. Now they can receive any texts sent to your number - whether from your bank or your friend. Yikes, right?

Signal stores your data in an encrypted form on your device. It can protect it in various ways. One of the most important protections is ephemerality - it can automatically delete your old texts. A text that is securely erased can never fall into the wrong hands if the device is compromised later.

An actively-compromised phone, though, could still give up secrets. For instance, what if a malicious keyboard app sent every keypress to an adversary? Signal is only as secure as the phone it runs on – but still, it protects against a wide variety of attacks.

Untrustworthy communication partner

Perhaps you are sending sensitive information to a contact, but that person doesn’t want to keep it in confidence. There is very little you can do about that technologically; with pretty much any tool out there, nothing stops them from taking a picture of your messages and handing the picture off.

Environmental compromise

Perhaps your device is secure, but a hidden camera still captures what’s on your screen. You can take some steps against things like this, of course.

Human error

Sometimes humans make mistakes. For instance, the reason a reporter got copies of messages recently was because a participant in a group chat accidentally added him (presumably that participant meant to add someone else and just selected the wrong name). Phishing attacks can trick people into revealing passwords or other sensitive data. Humans are, quite often, the weakest link in the chain.

Protecting yourself

So how can you protect yourself against these attacks? Let’s consider:

• Use a secure app like Signal that uses strong end-to-end encryption where even the provider can’t access your messages
• Keep your software and phone up-to-date
• Be careful about phishing attacks and who you add to chat rooms
• Be aware of your surroundings; don’t send sensitive messages where people might be looking over your shoulder with their eyes or cameras

There are other methods besides Signal. For instance, you could install GnuPG (GPG) on a laptop that has no WiFi card or any other way to connect it to the Internet. You could always type your messages on that laptop, encrypt them, copy the encrypted text to a floppy disk (or USB device), take that USB drive to your Internet computer, and send the encrypted message by email or something. It would be exceptionally difficult to break the privacy of messages in that case (though anonymity would be mostly lost). Even if someone got the password to your “secure” laptop, it wouldn’t do them any good unless they physically broke into your house or something. In some ways, it is probably safer than Signal. (For more on this, see my article How gapped is your air?)

But, that approach is hard to use. Many people aren’t familiar with GnuPG. You don’t have the convenience of sending a quick text message from anywhere. Security that is hard to use most often simply isn’t used. That is, you and your friends will probably just revert back to using insecure SMS instead of this GnuPG approach because SMS is so much easier.

Signal strikes a unique balance of providing very good security while also being practical, easy, and useful. For most people, it is the most secure option available.

Signal is also open source; you don’t have to trust that it is as secure as it says, because you can inspect it for yourself. Also, while it’s not federated, I previously addressed that.

Government use

If you are a government, particularly one that is highly consequential to the world, you can imagine that you are a huge target. Other nations are likely spending billions of dollars to compromise your communications. Signal itself might be secure, but if some other government can add spyware to your phones, or conduct a successful phishing attack, you can still have your communications compromised.

I have no direct knowledge, but I think it is generally understood that the US government maintains communications networks that are entirely separate from the Internet and can only be accessed from secure physical locations and secure rooms. These can be even more secure than the average person using Signal because they can protect against things like environmental compromise, human error, and so forth. The scandal in March of 2025 happened because government employees were using Signal rather than official government tools for sensitive information, had taken advantage of Signal’s ephemerality (laws require records to be kept), and through apparent human error had directly shared this information with a reporter. Presumably a reporter would have lacked access to the restricted communications networks in the first place, so that wouldn’t have been possible.

This doesn’t mean that Signal is bad. It just means that somebody that can spend billions of dollars on security can be more secure than you. Signal is still a great tool for people, and in many cases defeats even those that can spend lots of dollars trying to defeat it.

And remember - to use those restricted networks, you have to go to specific rooms in specific buildings. They are still not as convenient as what you carry around in your pocket.

Conclusion

Signal is practical security. Do you want phone companies reading your messages? How about Facebook or X? Have those companies demonstrated that they are completely trustworthy throughout their entire history?

I say no. So, go install Signal. It’s the best, most practical tool we have.

This post is also available on my website, where it may be periodically updated.