See also the Secure Messaging page for information on other messaging apps such as WhatsApp, Threema, Session, Briar, Olvid, Google Android Messages, Facebook Messenger, Apple iMessage, Telegram and more. My proposal for a safer alternative is also there.

The Secure Messaging page also has a long list of the limitations of secure messages. That is best read for context, before going into any specifics of Signal.

The information here was previous on the Secure Messaging page and was moved here March 30, 2025. As I got up to speed on Signal, and greatly expanded the information here, it seemed the right thing to do.

Signal does encrypted messages (both one and one and group chats) and phone calls between Signal users. It runs on Android, iPhones and iPads. A recent update added a desktop version which requires you first have the mobile version.

Amongst techies, Signal is well regarded for security and encryption. In fact, Signal is worshiped like a religion despite using phone numbers as userids and the obvious lack of anonymity. For many years, techies ignored the lack of anonymity. Beats me why. It can be critically important to hide who you communicate with. This strikes mes as a classic nerd mistake, to focus on technology (encryption in this case) and ignore the human need to be anonymous. That said, in 2024 Signal started to roll out a new userid feature to sort-of, kinda, replace phone numbers. Phone numbers are still needed, but there are now many options to hide them.

Signal has two different ways to identify a user when starting to communicate with them. After the communication has been established, there are three (more?) different thingies that might be used to assign a name to the person you are talking to. And, some of these thingies have more than one name. Who's on First? All told, Signal has

1. phone numbers
2. usernames and display names and chosen names
3. profiles and profile names
4. nicknames
5. safety numbers
6. PINS

Seems like a lot. Quoting from Signal documentation: "Usernames in Signal are a bit different than usernames in other services. A username is simply a way to initiate contact on Signal without sharing your phone number. It is not the profile name." But is a profile name the name of a profile or a persons public name in their profile? For help, see Understanding every one of Signal’s identifiers by Dr. Martin Shelton for the Freedom Of The Press Foundation (Published Sept. 25, 2024 Updated March 3, 2025).

There also seems to be a design flaw in the Nickname feature - it allows duplicates. That is just an accident waiting to happen. You can see some duplicates in this article by Joseph Cox for 404 Media: You Need to Use Signal's Nickname Feature (March 26, 2025). While touting the feature, Cox fails to mention the danger in having duplicate (or triplicate) Nicknames.

There is a known thing in software. As the requirements change, the software/system gets more and more complicated. An simple original design ends up looking like spaghetti as it is modified and modified again to fit new requirements. At some point, the right thing to do is just start over from scratch with a newer design, one specific to all the newer requirements. I wonder if adding user names to Signal was the straw that will break the camel's back. Perhaps a competing program that never involved phone numbers at all (there are many on this page), and has just one userid, will end up replacing it.

You can see how sorting out the many different identifiers might be a bit too much for non techies. Need proof? See the SignalGate topic below.

• March 25, 2025: Trump administration accidentally texted secret bombing plans to a reporter by Jon Brodkin for Ars Technica
• The few qualified techies who commented on the above story pointed out why Signal is not approved for classified US Government use - the phone can be hacked. Any mobile app is only as secure as the operating system it runs on. Perhaps the most desired phones to hack into, in the world, are those of the people in the above government chat. Who would not want to know the non-public thoughts of the Secretary of State? My solution to this is below (hint: Chromebook in Guest Mode).
• March 24, 2025: Matt Blaze, a professor of Computer Science, commented on Signalgate on Mastodon:
  "Signal provides:
  - Excellent protection against third party interception of communications (wiretapping)
  - Limited protection against compromised (hacked) or lost devices
  - No protection against certain common usage mistakes (accidentally including a reporter in your large group war planning chat)"
  He left out the shit documentation because, as a professor of computer science, he does not have a non-techie perspective.
• March 24, 2025: Matt Blaze also said
  "If you look at the systems that are supposed to be used for classified communications, the underlying cryptography isn't particularly different from Signal (the AES cipher can be used to protect classified material). That's not what failed here.
  The difference is that systems like Signal are designed to *facilitate* communication with anyone.
  Classified systems are designed to *limit* communication to authorized recipients.
  Both are sensible for their respective - very different - purposes."

Usernames were introduced in early 2024. If you learned about Signal before that, you have some catching up to do.

• You can only have one username at a time
• Signal says "Usernames are only to initiate a chat" So no audio or video?
• Can people see your username? It's complicated
• Can people find your username? Not in Signal, there is no searchable directory of usernames. I put mine on my personal website. And, in my Mastodon profile.
• You can change or delete your username, but no one is notified if you do
• Usernames can be between 3 and 32 characters, must include at least two digits at the end, can only contain letters, numbers and an underscore (no dashes), and, finally, are case insensitive. Not clear if the 32 character limit includes the period and the numbers at the end.
• The default format is xxxx.99 where xxxx are letters, followed by a period and two digits. If you leave out the digits, they are auto-generated (randomly?). You can specify the digits and I have seen usernames with 3 and 4 digits. How many digits can there be? Dunno.
• If someone reaches out to you by username and you accept the request, your username will be replaced in the chat by the name in your Signal profile. The other guy may see your phone number, or not, it depends on how the app is configured.
• Usernames and profile names are totally different things
• The name that other people see for you in Signal is determined by whether they have you in their contacts. If they do, the name they gave you in their contacts app, is what they will see as your name in Signal. If they do not, they will see the name you gave yourself in your Signal profile. Then again, nicknames. This is too hard.

March 3, 2025 (last update); Why journalists should enable Signal usernames by Dr. Martin Shelton for the Freedom Of The Press Foundation. Originally published Feb. 21, 2024. Quoting: "By default, Signal will no longer make your phone number visible to everyone you chat with. To start a conversation with someone, instead of giving your phone number, you can now use your own username to hand out to people ... You can optionally require people to find you via username instead of phone number..." The article has instructions and screen shots for configuring Signal.

• February 19, 2025: Bad guys targeting Signal users: Signals of Trouble: Multiple Russia-Aligned Threat Actors Actively Targeting Signal Messenger by Dan Black of the Google Threat Intelligence Group. Russian hackers are compromising Signal accounts using the built-in "linked devices" feature that enables Signal to be used on multiple devices concurrently. Linking an additional device typically requires scanning a QR code, so victims are sent a QR code that will deliver future messages to both the Russians and the victim. Google said one target of this scam are Ukrainian military units. The latest version of Signal on iOS and Android has some new protections from this scam. The same approach is also being used by the Russians on WhatsApp and Telegram users. Read more about Linked Devices from Signal.
• March 26, 2025 (last review): How to: Use Signal from the EFF. Long and detailed. A must read. Note this writeup is as of Signal version 7.0. As of March 2025, the latest Android version of Signal was 7.37.5, so this may be old.
• July 12, 2024: A bad look for Signal. Signal encryption key vulnerability being fixed on Mac (and less fully on Windows) by Ben Lovejoy for 9 To 5 Mac. Both the Signal macOS and Windows apps are not using great security. The encryption key for locally stored messages is stored on the machine in a plain text. Security researchers have been pointing to this vulnerability for at least six years. They had to be shamed into fixing this.
• 2024: The Signal website is miserable to useless for a newbie to the software. I see this sort of thing all the time, experts can not understand the perspective of someone new to the subject. When experts write documentation, we get a cheat sheet for experts. We do not get anything that helps a newbie get up to speed.
• November 8, 2023: Can you teach an old dog news tricks? Signal tests usernames that keep your phone number private by Sergiu Gatlan for Bleeping Computer. Yes and No, seems to be the answer. Signal has a setup an all new test environment for supporting usernames. However, you have to sign up for a new account in their test environment using a phone number and the option to hide your phone number is OFF by default. The feature seems to be a long way off.
• In October 2022, Graphene OS tweeted about why they do not include Signal in their operating system (a clone of Android without anything from Google included). On a technical level, their points are over my head, except for the fact that Signal is dropping support for SMS/MMS. Even without fully understanding it, they make the point that Signal is far from perfect. Quoting "Signal is now dropping support for SMS/MMS. They also don't care much about keeping their dependencies patched, reducing attack surface or internal sandboxing. It would be an issue for GrapheneOS ... They've made many decisions we disagree with including replacing registration lock PIN with a sync PIN, depending on SGX for security, using SGX as a replacement for the previous private contact discovery and making the secure local backup system in the Android app less useful."
• In August 2022, Twilio was hacked and Signal depends on Twilio to validate phone numbers. See their account: Twilio Incident: What Signal Users Need to Know of the incident. Phone numbers of roughly 1,900 Signal users were exposed to the Twilio breach attacker, who could have attempted to register them to another device. One solution is to on a Signal PIN and enable Register Lock. I read the doc and have no idea what this is or does. I have to wonder if Signal is too big and complicated for non techies to use safely. As for a checklist, in Signal do: Settings -> Account -> Registration Lock and verify that it is enabled.
• February 8, 2021: How to Make Your Signal Chats as Secure as Possible by Tim Brookes for How To Geek. Topics: Enable Registration Lock to Protect Your Signal Account, Verify Who You Are Talking To, Use Disappearing Messages to Avoid Leaving a Trail, Notifications May Breach Your Privacy, Lock the Signal App and Hide Content in the App Switcher, More Security Tweaks for iPhone Users, Remotely Sign out Linked Devices, Want to Use Signal Anonymously? Register Another Number, Take Precautions to Secure Your Smartphone, Too, Make Sure That Contacts Take Security Seriously, Too
• June 18, 2020: I don’t trust Signal by Jan Harasym. The author makes a lot of very good arguments. Perhaps the most striking to me was about open source software. Yes, Signal is open source ... in some respects. But not in all respects and probably not the way people assume. Of course, there is the issue of phone numbers. He also points out that the way Signal encrypts your contact list is poor. And, he makes the same observation that I do, that support for Signal seems like a cult. His term is that there is too much support for it. We saw nerd cult behavior with OpenVPN which was the greatest flavor of VPN ... until WireGuard came out, at which point we finally started to hear bad things about OpenVPN. Quoting the blog: "... I am not saying Signal does anything bad, I am really just saying that they could do harm; and the only thing that says they won't is 'trust me' ... I don't think any individual issue I’ve mentioned here is a dealbreaker, and most in isolation can be argued away. For me, though, in the larger context ... I can't really say that I have full faith in Signal. It's fine for me as an insecure messenger, but the user experience is just worse than other insecure messengers. I don't personally have any reason to trust it more than Telegram; other than that people get mad when you say that. Which, is incredibly unconvincing."
• August 2019: This article, by Vladimir Katalov of Elcomsoft, shows the Signal security is not perfect: How to Extract and Decrypt Signal Conversation History from the iPhone. Perhaps things have changed since it was written? I don't know.
• May 2017: If you do use Signal, there are quite a few dos and don'ts. This article by Micah Lee was a good guide at the time. I don't know how much of it still applies since the software has no doubt changed in the years since. How to keep your chats truly private with Signal.

1. The Android app store has many apps with the same or similar names. To insure you download the right app, look for "Signal Private Messenger". Also, make sure it is from the Signal Foundation, has over 2 million (2M) reviews, is marked as an Editors Choice and has over 100 million (100M+) downloads.
2. Every now and then you should check the Linked Devices (in the Settings) to insure that a device you don't own, has not been added to your account.
3. Hide your phone number: Settings -> Privacy -> Phone number
4. Every now and then verify the account PIN. Without it, someone can steal your account using assorted tricks with phone numbers
5. Enable Screen Lock and Registration Lock
6. Disable link previews
7. Maybe disable Chat backups (it is disabled by default)
8. Maybe enable Disappearing messages. Read the doc, not all messages in a chat may disappear. There is one time value for your account and each chat may have a different time value.
9. Hide the app: As noted above, Android 15 and iOS 18 both introduced ways to hide the existence of apps installed on devices. That would be a good thing to do for the Signal app. The Android 15 implementation of app hiding is more secure than that in iOS 18 because it allows for a unique app-run password.
10. Lock the app on Android 14: As of Signal app version 7.37.5 (current as of March 2025), the Signal Screen Lock feature is not very useful. Still, you are a small bit more secure with it on. The problem with the feature is that, rather than its own app-run password (my terminology) the app unlocks using the same code/fingerprint that unlocks the phone. Also, the time period for the app to lock itself up is no faster than one minute, it should be faster than that.
11. Lock the app: Good old days: Back in May 2017, Micah Lee wrote: Cybersecurity for the People: How to Keep Your Chats Truly Private With Signal where he described how the Android version of Signal let you lock down the app with a separate passphrase to access it. Since then, this feature was removed. It was at: Settings -> Privacy -> Enable passphrase.
12. Android: At Settings -> Privacy, enable the Incognito keyboard
13. Screen security: On Android, turn it on at Settings -> Privacy. On iOS, a similar option is called "Enable Screen Security"
14. If using a VPN with Signal (a good idea) consider changing VPN servers as often as you can tolerate doing so
15. Always Relay Calls: This feature is said to route calls through Signal servers so as to hide your IP address. I don't have a recommendation here as I don't see that it does anything that a VPN would not. The EFF says it is a good thing: " By default, Signal uses peer-to-peer calling, which can leak your IP address to the other caller. If that caller is not in your contacts list, Signal defaults to an option that relays the call through their service, hiding your IP address. But you can also enable this for every call, if needed." They say nothing about a VPN and nothing about messaging, as opposed to calling. So, dunno
16. There are many configuration settings for Signal Notifications. One set is for calls, another set is for messages. Review them all,g at least once.
17. Use nicknames, the longer the better. How long can a nickname me? According to the Signal Foundation, that is none of your damn business.
18. The EFF suggests auditing keyboards: "audit any keyboard you've installed in the past and perhaps forgotten about. If you do not need them, use them, or know enough about the keyboard app to feel comfortable using it, it's best to remove it." The article has step by step instructions.

March 3, 2025: Locking down Signal by Dr. Martin Shelton for the Freedom Of The Press Foundation. Originally published Nov. 9, 2018.

January 14, 2021: Switching to Signal? Turn on these settings now for greater privacy and security by Adrian Kingsley-Hughes for ZDNet

• The Signal website is signal.org. Someone named Scott Day of DigiMedia.com, LP owns signal.com. The Signal Foundation is not associated with signal.io or signal.net or signal.tv. As of March 30, 2025, the signal.app domain is available for purchase.
• You can not put the same account on two phones so all your Signal eggs are in one basket should the phone be lost, stolen or damaged. To register the same number on a replacement phone, you need the PIN.
• There is a Transfer Account feature for when you get a new phone. Based on the instructions in the Android app (version 7.37.5) it only works for transferring to another Android device.
• Two Signal accounts on one device: There is an Android app called Molly that is a fork of Signal. On the September 16, 2022 episode of his Privacy, Security & OSINT podcast, Michael Bazzell discussed how he uses it so that there can be two different signal accounts on the same Android device. Molly is not in the Play Store and even installing it from F-Droid is not standard. On Linux, he uses SNAP to have multiple copies of Signal and multiple interdependent Signal accounts on the same copy of Linux. On macOS, the regular and Beta copies of Signal are separate, so installing each lets you have two Signal accounts on a single copy of macOS.
• The term "Profile name" has two meanings in Signal. One refers to the name of a Notification Profile. The other is the name you give yourself in your Signal profile.
• The is a Signal Community at community.signalusers.org
• r/signal on Reddit is an unofficial subreddit run by the Signal user community. It is not affiliated with or endorsed by the Signal Foundation or Signal Messenger LLC. Their FAQ shows just how much there is to know to use Signal. There should be a test.

What does Signal know about who you communicate with and when?

• October 29, 2018: Technology preview: Sealed sender for Signal by jlund of Signal. At the time this article was written, Signal did know who was messaging whom. This blog is about their upcoming plans to change that. But, in March 2025, I could find nothing newer on the subject from Signal. WTF? Are they just lazy at documentation? Or maybe the usefulness of "sealed sender" is exaggerated? The article says that Signal does not store a record of your contacts, social graph, conversation list, location, user avatar, user profile name, group memberships, group titles, or group avatars.
• November 20, 2023: Signal knows who you’re talking to by Lambert (aka the Sane Security Guy). The article argues that the "Sealed Sender" feature is a sham. Quoting: " [the] Sealed Sender ... feature is very technically complex, and totally useless. While Sealed Sender is pretty complicated under the hood, the result of it is one-way anonymity ... when Phone Number A sends a message to Phone Number B, Signal won’t know that the message is coming from Phone Number A and will only know that the message is to be delivered to Phone Number B. It does this in a way that’s very similar to snail mail without a return address: the letter inside the mail envelope might tell the recipient who the sender is, but the mail envelope itself tells the post office only who the recipient is .... The problem comes up when multiple messages are being sent back-and-forth ... Sealed Sender only protects the sender’s phone number; it does not protect the sender’s IP address ... " There is no techie jargon in the article and I highly recommend every Signal user read it. Near the end, Lambert discusses Signal delivery receipts, which really makes Sealed Sender seem like a scam.
• March 28, 2025: Signal Downloads Spike Since Trump Team Scandal - But It’s Not A Magic Bullet by Tony Bradley in Forbes. Signal tries to obscure user metadata. Not a surprise. It does not store message contents or contact logs. I employs techniques like sealed sender to obscure traffic patterns. Complete metadata invisibility is not technically possible. ISPs and global surveillance networks can still learn when you're online, how often you message certain contacts or your physical location based on IP address. These breadcrumbs can be surprisingly revealing.
• If you use iCloud on iOS and you do not want to share the Signal call history (including who spoke to whom and when), then disable the option to "Show Calls in Recents"
• From Signal Terms & Privacy Policy, "Signal queues end-to-end encrypted messages on its servers for delivery to devices that are temporarily offline .... " Can they be compelled to turnover the list of what is currently queued up? That is not addressed here. The article says that "Your message history is stored on your own devices." It does not say anything about the message history maybe, perhaps, possibly being also stored elsewhere. Sloppy? Or on purpose? As of March 2025, this was last updated in May 2018. The software is likely to have been drastically changed since then.

For a long time, people have been looking to use Signal without divulging their cellphone number. As of the early 2024 introduction of Signal usernames, the use of phone numbers is not the huge problem it previously was. Sometimes a Google Voice phone number works, sometimes not. Note that a new Signal account can be created using a land line - Signal will just call you with the temporary code rather than texting it (last verified in March 2025).

• August 2, 2024: How to Use Signal Without a Phone Number? by Alex Smith of Calilio. The title is mis-leading, is about not using your actual cellphone number. The article suggests these free virtual phone number providers: Calilio, Google Voice, TextNow, FreeTone and 2ndLine. Note: In the article below, the author found that Google Voice did not work.
• July 16 2024: How I Got a Truly Anonymous Signal Account by Nikita Mazurov for The Intercept. An anonymous Signal account is a huge ask. You can not use temporary SIM cards, virtual eSIMs or virtual numbers because these all leave a payment trail. The solution: a pay phone. Not just any pay phone, but one that accepts incoming calls. Not easy to find. The article also discusses using PIN for locking the Signal account.
• October 2021: This blog by Yael Grauer How To Use Signal Without Giving Out Your Phone Number Using a Chromebook and an Old Phone points out many of the problems with the Signal app. Her solution is ridiculous and it too shows why Signal is a poor choice.
• September 2017: Using Signal Without Giving Your Phone Number by Martin Shelton on Medium
• September 2017: How to use Signal without giving out your phone number by Micah Lee for The Intercept.
• August 2017: How to Use Signal Without Giving Out Your Phone Number: A Gendered Security Issue by Jillian York for Vice

These articles are from Signal. None have a creation date. None has a last updated or last reviewed date. None state which version(s) of the software they apply do. This is disgraceful. It is amateurish and not something that engenders trust. Oh, an its pretty awful to boot. Lots of click-here-type-this information, very little on concepts.

1. Register a phone number The interesting thing here is that the phone must able to either receive an SMS text message or a phone call. That means a land line can be used to register a new Signal account. I have not seen that tidbit reported anywhere.
2. Phone Number Privacy and Usernames says "As a new default, your phone number will no longer be visible to everyone in Signal". The word "new" has no meaning at all on a document without a date. One exception is that people who already have your Signal phone number saved in their OS contacts will still see your phone number. If you want the world to know your phone number, this is now an option. The article also says that you can limit who can connect with you on Signal.
3. Set and manage disappearing messages
4. Delete messages, alerts, or chats
5. Linked Devices
6. Signal Profiles and message requests
7. What is a safety number and why do I see that it changed? Their explanation makes no sense to me. Quoting: "Each Signal one-to-one chat has a unique safety number that allows you to verify the security of your messages and calls with specific contacts. Verification of safety numbers is a good security practice for sensitive communication. If a safety number has been marked as verified, any change must be manually approved before sending a new message." A safety number only applies to 1-on-1 chats. Does it apply to voice calls? Video calls? Not clear. A safety number lets you verify "security". WTF? Does it verifying the ID of the person at the other end? The in-flight encryption? The device being used at the other end? Not clear. The whole concept is not clear. As I noted above, the Signal website is all but useless to someone new to the software. Just miserable.
8. Keep your phone number private with Signal usernames a blog by Signal. This article has a date. Someone must have screwed up :-) February 20, 2024. About new options that should roll out sometime in 2024. A new default: phone numbers will no longer be visible to everyone. A new username feature can be used instead. The user name is NOT displayed in chats, instead the profile name is. If you don’t want people to find you by searching for your phone number, there is a new setting for that.