Verifiable Secret Redistribution for Threshold Sharing Schemes

We present a new protocol for the verifiable redistribution of secrets from (m,n) to (m # ,n # ) access structures for threshold sharing schemes. Our protocol enables the addition or removal of shareholders and also guards against mobile adversaries that cause permanent damage. We observe that existing protocols either cannot be readily extended to allow redistribution between different access structures, or have vulnerabilities that allow faulty old shareholders to corrupt the shares of new shareholders. Our primary contribution is that, in our protocol, new shareholders can verify the validity of their shares after redistribution between different access structures. Keywords: threshold secret sharing, verification, proactive security