Capacity of a shared secret key

Shannon theoretic shared secret key generation by multiple terminals is considered for a source model in which the components of a discrete memoryless multiple source and a noiseless public channel of unlimited capacity are available for accomplishing this goal. A shared secret key is generated for distinct coalitions of terminals, with all the terminals cooperating in this task through their public communication. A communication from a terminal can be a function of its observed source component and of all previous communication. Member terminals of a coalition unite in recovering the key. Secrecy is required from an eavesdropper that observes the public interterminal communication. A single-letter characterization of the shared secret key capacity is obtained. When the key must be concealed additionally from subsets of coalition members, we provide an upper bound for the strict shared secret key capacity.