A proactive threshold secret sharing cryptosystem using a set of servers. The cryptosystem is a threshold cryptosystem, in the sense that service is maintained if at least (k+1) out of n servers are active and honest. The secret signature key is compromised only if the adversary breaks into at least...http://www.google.de/patents/US5625692?utm_source=gb-gplus-sharePatent US5625692 - Method and system for a public key cryptosystem having proactive, robust, and recoverable distributed threshold secret sharing
