I am a frequent user of Signal but I met a situation where a friend, let's call this Bob, also a Signal user, wanting to talk with me using Signal. We could chat but we could not talk to him. I have no trouble with have a voice conversation using Signal with other users using public Internet services. Attempts to connect to or from Bob always fail. He was using Signal in a campus network and I suspect the reason for these failure was due to certain ports required by Signal calls to go through being been blocked. Bob also uses Skype and there is no problem of striking up a crystal clear voice conversation with him using that.
So I am wondering whether other so called private messengers supporting E2EE on voice call will suffer from the same problem?
After waiting for Bob to upgrade his Android machine from his old Android 4.0 machine, as an experiment he installed Wire Messenger, one that I also use, showing great promises, and I have great respect for it. This messenger also uses the Signal protocol to perform E2EE and it has far more features than Signal. However, it is not as widely known as Signal and definitely less than WhatsApp.
Finally, Bob and I successfully managed to talk securely using Wire protected by Signal protocol transversing the same tightly protected network. We've decided to give Signal a miss because the new phone is now a full populated due SIM, see comments below.
So if anyone having trouble talking with Signal, give Wire a try and you even can test it using your web browser. For those not familiar with Wire, Wire has several great benefits that Signal and WhatsApp fail to offer:
Benefits
✔ Work without dependent of SIM or phone number
Unlike Signal & WhatsApp, it uses an e-mail address as the identifier with name and phone number as optional identifiers. These optional identifiers can be change at will; the phone number you enter can be different from that in the SIM.
Moreover, the e-mail is only used during account registration for receiving the verification code. After that it is just a pure identifier, like the mobile number used in WhatsApp or Signal.
You can look up friends base on e-mail address, name, or number.
✔ Because of its independence on SIM, its desktop version is a totally stand alone program, unlike Signal and WhatsApp where theirs are appendages to their smart phone siblings.
✔ Because of that, you can run Wire totally from a web browser without having to establish an account in a smart phone. No need to install anything. It is a great bonus for being able to walk up to the airport kiosk and start chatting.
✔ Access to your phone's Contacts is totally optional because its primary identifier is the e-mail address and not phone number. However, if you grant it access to the Contacts, it can use the Contacts data to look up friends.
✔ Its oblivion of a SIM is a great bonus for those operating a dual-SIM phone. Because it does not rely on the SIM, it can be used in a dual-SIM phone without the usual chaos associated with SIM dependent messengers.
If you are in a situation with a dual SIM phone, switch over to Wire and you can use the phone to the fullest rather than carrying two phyiscal phones just to escape the madness.
✔ Because it does not care about the SIM, it is a great tool for travelers who likes to use local SIM. One does not have to do anything to continue the conversation.
✔ At the time of writing and testing (Signal 3.22.2 and Wire 2.22.298) Wire is the only one with encrypted video conferencing and file attachment.
Disadvantages
❌ Since most private messengers use encryption using various schemes to provide content integrity and safest, the degree of its privacy is now measured based solely on how much meta data the messenger retains, for how long and its purpose. Meta data are essential for the system to operate correctly. It is the system retention policy of these data or portion of them that have effect on its degree of privacy.
According to this measure, Signal ranks supreme and as the ultimate private messenger. A recent grand jury demand in US lay bare the amount of data retained by Signal - the date the user first registered and the last time the user contacted the system (it does not even record the participant of the conversation).
No messenger so far has ever published verifiable data to surpass Signal or even dare to challenge its supremacy. If you do not hold data how can one be forced to hand over the data? The best defense against authority demanding to hand over data as opposed to data retainer's expensive court fight.
While Wire has declared what kind of meta data (Creator, Timestamp, Participants list, and Conversation name) it records, it has not declared the retention period and the purpose of retaining them. As can be demonstrated, Wire collects tons of data by comparison to Signal and as a result less private and thus secure than Signal.
In fairness, what Wire collects is probably small by comparison or typical of what other messengers, such as WhatsApp, Wickr, etc, collect. At least Wire declares precisely what are being collected without explanation of the purpose rather than some general non-specific statement from WhatsApp, who even attempts, but aborted, to share data with its master.
❌ Small user base.
This can be a bonus if you really want a private private messenger without being bombarded by tons of conversations. This is not a reflection of Wire's lack of technical excellence but more human inertia to change - a Network Effect. It also demonstrates the bulk of messenger users pay little attention to encryption and meta data retention.