Voice calls over GSM

Hello, does Purism Librem 5 provide encryption for voice calls over GSM network between two Purism Librem 5?

No, they don’t. You would need an end-to-end-encrypted communication application capable of voice calls (caller and recipient) to do that, and it would probably require an LTE connection, i.e. 4G, not 2G GSM.

A bit of semantics, but GSM calls are encrypted. The old 2G encryption just isn’t what today passes as good. 3G is better and 4G (and 5G) use better encryptions than the previous generations for voice calls. It’s in the standards, so they are done in the modem and not by Purism, so the answer could also be “no”.

Yes, I’m sure the OG was meant to be about end-to-end encryption, as Amarok surmised already. However, if memory serves, although LTE and data for such is the preferred modern choice, couldn’t some sort of analog signal be transmitted over voice for e2ee…? I’m thinking back to the oldendays of landline communications (not sure if it’s applicable over digital processed voice).

To be helpful, why don’t we start a list of all the apps (and/or methods) that can be used for e2ee voice using L5. Those that work well and those that need work alike.


It could, but it would be very wasteful as you’d have to fight the audio codec trying to compress it, likely ruining your data in the process. You’d also have to handle several codecs, not just a single specific one, as calls can be transparently handed over through technologies (VoLTE dropping to 3G dropping to 2G and the other way around, all using different codecs).

The whole audio path is available on the CPU through PulseAudio, so you just need two Librem 5s and you could easily experiment with processing data to pass as audio :wink:

If memory serves me, i believe it has already been done. A quick web search seems to confirm this, turning up research papers and software projects on the topic of sending encrypted data through a GSM voice channel.