A member of the group that intends to become active does so by pushing her/his share of the group key into the kernel. The TCFS module checks if the number of shares available is above the threshold and, if it is so, it attempts to reconstruct the group encryption key. By the properties of the Threshold Secret Sharing Scheme, it is guaranteed that, if enough shares are available, the group encryption key is correctly reconstructed. Once the group encryption key has been reconstructed, the files owned by the group become accessible. Each time a member decides to become inactive, her share of the group encryption key is removed. The TCFS module checks if the number of shares available has gone under the threshold. In this case, the group encryption key is removed from the TCFS module and files owned by the group become unaccessible.
The current TCFS implementation of the group sharing facility requires each member to trust the kernel of the machine that reconstructs the key to actually remove the key once the number of active users goes below the threshold. Future implementations will remove this requirement by performing the reconstruction of the key in a distributed manner.