Table 2. The notations and meanings.

Notation	Meaning
$\lambda$	Security parameter
N	Augmented vector dimension
$msk$	Master secret key
$us{k}_{ID}$	User’s secret key (associated with ID)
Q	Hierarchical parameter
$b_{ID}$	Session sub-key (associated with ID)
$q_{ID}$	Access level parameter (associated with ID)
$v_k$	Vector k
B	Session sub-key
${\sigma }_k$	Signature corresponding to vector k