A medical ad hoc wireless network (10) is deployed in a healthcare medical facility surrounding individual patients and including wireless nodes (A, B, . . . , Z). Before deployment, each node (A, B, . . . , Z) is pre-initialized with a public key certificate (22) and offers a trust and symmetric key distribution service (32). In joining the ad hoc network (10), a node (B) authenticates and registers to one randomly self-chosen node (A) by using certified public keys (20). Such node (A) becomes Trusted Portal (TPA) of the node (B). The node (B) dynamically registers to a new self-chosen TP node when its old TP node leaves the ad hoc network (10). The network (10) supports symmetric key authentication between nodes registered to the same TP node. Additionally, it supports symmetric key authentication between nodes registered to different TP nodes.