Table 4. Notations used in the proposed scheme.

Symbol Definition
Ui User i
IDi User’s identity
TIDi Transformed identity of Ui
PWi User’s chosen password
TPWi Transformed password of Ui
βi Biometric information
RA Authentication Authority
CA Authorization Authority
SNj Service node i
SIDi Service Identifier
TSk Service Type k
SRUi Secret key of RA for Ui
SRC Common Secret between RA and CA
SSk Service Type secret
h(.) One-way hash function
An XOR operation
|| String concatenation