Table 2 Notations used in the paper

WBAN

Wireless body area network

K_sk

Secret key preloaded in all sensors

WSN

Wireless sensor network

MAC

Message authentication code

EKG

Electrocardiogram is the interpretation of the electrical activity of the heart for a specific period

K _n and $K_{n^{\prime }}$

K _n is the key selected from the key pool, and $K_{n^{\prime }}$ is the hashed key obtained as a result of the hash of K _n

PV

Physiological value is a biological characteristic of the body

EK_SNa,_SN>_b

Pairwise key established between SN _a and SN _b

ID_SNa,ID_SNb, ID_ps, ID_SNs

Identifiers of sensor nodes a, b,personal server, and networkrespectively

nonce

Random number generated during the communication process tocheck the transaction freshness

MS

Medical server located in hospital

KeyRef

Broadcast message used to refresh key in the network

RBS

Remote base station

P

Key pool

CH

Cluster head

S

Subset of P

CM

Cluster member

R

Key ring

Intra-WBAN communication

The on-body communication

K _i

Randomly selected key from thepool

Inter-WBAN communication

The communication between two or more WBANs

HMAC

Keyed-hashing for message authentication

SN_a

Sensor node ‘a’

K _M

Master key

SN_b

Sensor node ‘b’

K _i ^′

Hashed key

PS

Personal server

ICK

Integrity check key

E_re

Residual energy

K _net

Network key for broadcastauthentication

T(n)

The number of competing nodes

P _r

Probabilities of occurrence of CH

E ₀

Initial energy

d

Distance from RBS