The user data confidentiality feature on physical connections is the property that the user information exchanged on traffic channels is not made available or disclosed to unauthorized individuals, entities or processes.
The purpose of this feature is to ensure the privacy of the user information on traffic channels.
Encryption will normally be applied to all voice and non voice communications. Although a standard algorithm will normally be employed, it is permissible for the mobile station and/or PLMN infrastructure to support more than one algorithm. In this case, the infrastructure is responsible for deciding which algorithm to use (including the possibility not to use encryption, in which case confidentiality is not applied).
When necessary, the MS shall signal to the network indicating which of up to seven ciphering algorithms it supports. The serving network then selects one of these that it can support (based on an order of priority preset in the network), and signals this to the MS. The selected algorithm is then used by the MS and network.
The ME has to check if the user data confidentiality is switched on using one of the seven algorithms. In the event that the ME detects that this is not the case, or ceases to be the case (e.g. during handover), then an indication is given to the user.
This ciphering indicator feature may be disabled by the SIM (see GSM 11.11).
In case the SIM does not support the feature that disables the ciphering indicator, then the ciphering indicator feature in the ME shall be enabled by default.
The nature of the indicator and the trigger points for its activation are for the ME manufacturer to decide.
During the establishment of a call the trigger point shall be at call initiation at the latest. In the case of handover the trigger point shall be the completion of handover at the latest.
The manufacturer may provide the means to enable the user to temporarily disable the feature. This should be done in such a way that the user can protect it from misuse.