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SIM cloning is often pointed out when suspecting someone may have captured an SMS with an one time password or authentication code, without proof.

I find it hard to believe that the phone network would allow two phones to register with the same IMSI & ICCID and actually deliver calls or messages to both of them. To me, that would either trigger some red flags, automatically ban the IMSI/ICCID to protect the customer or thwart abuse (like using two devices simultaneously on the same mobile plan) or at the very least make the second device not working because the network doesn't know how to handle this undefined behavior and can't register the second device.

Now, assuming the SIM itself was compromised and its secret key is out, does anyone have some proof on whether it's actually possible to use the second clone SIM to eavesdrop on the real SIM's communications ?

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1 Answer 1

You can find some information on this StackOverflow thread.

There cannot be two IMSI active at the same time, and the operator will not fork the communication to the two phones. So not eavesdrop.

Depending on the operator and contract, when a second phone shows up with the same IMSI, it may either be refused to connected the cell phone network, or be allowed but in this case it will be the previous one which will be disconnected (allowing to switch a single line over several SIM cards, for instance one for the cellphone and another for a phone installed in a car).

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