Interesting... Nice that IOS gives you a warning. I wonder if Android does the same?
It's called 'Ciphering Indication Feature' – and can be suppressed on the network side … so you can assume that an IMSI catcher ('Stingray') will not let your mobile know that it is using no or weak encryption.
It's actually a bit set on the SIM card, nothing to do with the network. Check out GSM 11.11, 10.3.18
Thanks, you are of course right. I should have written network operator. The operator can turn on/off OFM on the SIM.
Technically yes, but if you're talking about a stingray then I don't think they're going to have the ability to alter your sim card without authenticating with it; which is a lot harder than just using a null cipher over the air.