I'm currently studying the A5/1 algorithm used for GSM encryption. I understood how thanks to the symmetric private Key and a public counter frame one can encrypt the communication between A and B.
However, what I don't really understand is how the symmetric private key K is managed ? If A wants to communicate with B. A and B have to share the same secret key K. Now, if A wants to communicate with C, A and C will have to share the same secret key. How does this key distribution is handled ? Does the phone company distribute them before the call ?