Escrowed Key Cryptosystems hold the promise of faithfully realizing legal guarantees of privacy for users under normal circumstances while at the same time insuring that privacy can be breached by authorities in special circumstances under appropriate legal safeguards. The most attractive feature of these schemes is that it is possible to ensure that the interests of each of the parties—the users, the law enforcement or national security agencies, the court or other monitoring entities and the escrow agents—can all be guaranteed up to the level of integrity of the protocol or cryptosystem. Unfortunately, the first scheme to attempt this, the Clipper protocol as adopted by the U.S., completely fails to do so for either the user(s) or for the monitoring entities. In this paper a new escrowed key protocol and new devices are described that verifiable protect the interests of all parties by positively implementing legal guarantees of privacy and access.

Several verifiable secret sharing schemes for threshold schemes based on polynomial interpolation have been presented in the literature. Simmons and others introduced secret sharing (also called shared control) schemes based on finite geometries, which allow istributing a secret according to any monotone access structure.