Encryption Theory and Methods

When discussing encryption, we need to differentiate over-the-air encryption (for example
when we use the A3/A5/A8 keys and encryption algorithm on the GSM SIM to provide
security over the radio interface) and end-to-end encryption (literally from user to
user), as shown in Table 9.3. If we require end-to-end encrypted traffic to be read in
plaintext by the network, then we need user keys to be stored by a trusted third party
and available to be used by the operators on behalf of authorities with a right of access.