Algorithm 3 Initiation Step 1.3 [HN]

Inputs:  $(SUCI,I{D}_{SN})$       Parse $SUCI$ as $C_0,C_1,C_2$       Compute a shared key $k_{HN}\leftarrow KDF(s{k}_{HN}·C_0)$       Parse the shared key $k_{HN}$ as $(k_1,k_2)$       Compute $MA{C}^{\prime }\leftarrow MAC(k_2,C_1)$       Check if $MA{C}^{\prime }=C_2$, Abort in the negative case. Otherwise, continue       Compute $SUPI\leftarrow DEC(k_1,C_1)$       Retrieve the corresponding k and $SQ{N}_{HN}$ based on $SUPI$    Outputs. HN outputs ⊥ if $MA{C}^{\prime }\ne C_2$, Otherwise, it output $k,SQ{N}_{HN}$.