Mastodawn

Matthew Garrett Aug 7, 2025

Two weird LTE auth questions that I'm sure someone here knows:

1) My understanding is that the mutual auth means relying on a SIM private key. But can't phones without SIMs get onto networks for emergency calls? Or can that be done without full authentication?

2) Is there anything at the protocol level stopping multiple identical SIMs joining the same network (private, unfederated) network? Multiple devices with different IMEIs but the same IMSI and cryptographic material

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lynxis

@mjg59

2) It might be possible. Paging must never use the IMSI and always S-TMSI.
Also higher up the stack there are constrains you will break. But if you only want to have many phones with the same IMSI in your single cell, I would try to look into srsEPC first. I don't know the code base of srsEPC, but it is a single daemon instead of 10 daemons.

Such constrains for e.g. a IMSI is often a unique id in internal structure to save phone capabilities. (auth, crypto, ...)