Mission-critical networks show great potential in emergency response and/or recovery, health care, critical infrastructure monitoring, etc. Such mission-critical applications demand that security service be “anywhere,” “anytime,” and “anyhow.” However, it is challenging to design a key management scheme in current mission-critical networks to fulfill the required attributes of secure communications, such as data integrity, authentication, confidentiality, nonrepudiation, and service availability. in this paper, we present a self-contained public key-management scheme, a scalable method of cryptographic key management (SMOCK), which achieves almost zero communication overhead for authentication, and offers high service availability. in our scheme, a small number of cryptographic keys are stored offline at individual nodes before they are deployed in the network. To provide good scalability in terms of the number of nodes and storage space, we utilize a combinatorial design of public-private key pairs, which means nodes combine more than one key pair to encrypt and decrypt messages. We also show that SMOCK provides controllable resilience when malicious nodes compromise a limited number of nodes before key revocation and renewal.