Editing P2p mobile carriers (section)

= 2. How authentication is done in mobile networks =

In the 2G/3G/4G/5G networks, authentication follows a challenge-response protocol using symmetric keys to encrypt challenges [aka-protocol]. Both the MS and the MsC have a copy of the same symmetric key and hence are able to encrypt the same challenge.

To authenticate a mobile user, the MsC generates a large random number to use as a challenge and sends it to the mobile user via the base station. The MS encrypts the challenge using the secret key stored in their e/U/SIM card, and returns the response to the MsC.

If the response is a correct encryption of the challenge under the right key, the MsC knows the mobile device must be in possession of the secret key and hence is allowed to join the network. The final stage involves generating a new key pair that is used for encrypting voice calls, SMS, and other commands sent over the air waves.

This is done by inputting the challenge and secret key into the right algorithm – the type of which has been previously negotiated between the MS and MsC. If no algorithm is supported between them, then the MS cannot proceed with the connection.
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All the different generation mobile networks follow the same basic protocol for authentication, however more sophisticated changes were made with 3G to allow the mobile device to authenticate the network, and various improvements were made on 4G and 5G to improve privacy.

Different generation networks have standardised algorithms for use with authentication and ciphering, but only ciphering must support specific routines, an operator can do authentication however they like.

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