Moreover the SPDM includes necessary fields to share the LBK and the tier.
Upon the reception of an authentic SPDM (Received [MAC.sub.TK](M) = Computed [MAC.sub.TK](M) and [K.sub.0]=H([K.sub.1])), the sensor node stores the received nodeID, tier, and LBK in its Secure Neighbors table.
Then, the receiver node generates its proper LBK and prepares the broadcasting of an SPDM by updating the LBK, the tier and the MAC fields.
The rebroadcast of the SPDM allows each sensor node to create secure links with its neighbors and share its LBK. Thereafter, all possible secure multi-hop paths are traced.
To ensure confidentiality, the new GBK is encrypted at each hop with the correspondent LBK. To be sure that the new GBK is really generated by the BS, the text which corresponds to the earlier cipher text is sent in clear.
A healthy node first erases the shared PWKs with the compromised nodes, and then generates a new LBK. A Secure Key Update Message SKUM is sent to each non compromised neighbor S to share the new LBK.
SKUM(S [right arrow] S'): NonceS, [Enc.sub.PWK](LBK), [MAC.sub.PWK](M)
Node S receives in turn, a Secure Acknowledgment of Key Update Message (SAKUM) from each healthy neighbor, say S', that confirms the sharing of the new LBK. Accordingly, a compromised node will not be able to interpret secure local broadcast messages.
A row in the neighbors table requires at most 40 bytes (nodeID, Tier, lastNonce, LBK, PWK).
For KMMR, each node has to share its LBK with its neighbor nodes by broadcasting a SPDM.
As a result, in SNEP a node at tier t requires to send 2t messages to share its PWK with a parent node, and 2t + 1 messages to share its LBK with a sibling node.