There are emerging needs of secure communications in mission-critical applications over wireless ad hoc networks, including battlefield communications, emergency rescue operations, and disaster recoveries. In these applications, it is important to support secure communications in "anywhere", "anytime" and "anyhow" manner with following attributes:
data integrity, authentication, confidentiality, non-repudiation, and service availability. Being good candidates to address these attributes, Public-Key Cryptography (PKC) schemes have advantages over the symmetric systems. However, characteristics of missioncritical ad hoc networks pose the following new challenges for the design: (1) Vulnerability to the SybilAttack : When the Sybilattack happens, an attacker can claim multiple identities and the fake identities can easily defeat reputation and threshold protocols, where a legitimate node must rely on majority of nodes to reach decisions. (2) Unreliable Communications and Network Dynamics: Due to shared-medium nature of wireless links, flows may frequently interfere with each other. Moreover, a network may be partitioned frequently due to node mobility and poor channel condition. (3) Large Scale: The number of ad hoc wireless devices deployed at an incident scene depends on specific nature of the incident. In general, the network size can be very large. In addition, an ad hoc network should be able to accommodate more mobile devices if necessary. (4) Resource Constraints: The wireless devices usually have limited bandwidth, memory and processing power. Among these constrains, communication bandwidth consumption and memory are two big concerns for key management schemes.