When UE initiates RRC reestablishment with cause integrity failure?

Question

Reestablishment will be initiated only after AS security then how integrity will be failed and how it initiates reestablishment?

Answer 1

After initial security activation, encryption and integrity both are imposed for outgoing signalling and data. UE data packets are encrypted while rrc messages are encrypted and integrity protected. Lets assume an encrypted and ciphered rrc message is sent to UE but somehow its integrity checks fails at UE, in that case UE triggers re-establishment procedure to re-set its radio link with eNodeB with new security keys.

Answer 2

Integrity failure can happen due to mismatch in COUNT-I between UE and ENodeB or if wrong keys are generated during handover (incoming from other RAT).

And of course it can also occur due to attacks from third party and that is what integrity is supposed to be there for....