import com.codahale.shamir.ExpandedScheme;
import java.nio.charset.StandardCharsets;
import java.util.Map;
class Example {
void doIt() {
final ExpandedScheme scheme = ExpandedScheme.of(5, 1, 3);
final byte[] secret = "hello there".getBytes(StandardCharsets.UTF_8);
final Map<Integer, byte[]> parts = scheme.split(secret);
final byte[] recovered = scheme.join(parts);
System.out.println(new String(recovered, StandardCharsets.UTF_8));
}
}Expanded Secret Sharing allows to split secret S into N parts, of which M are mandatory
to reconstruct S and K-M are optional in the recovery process. Mandatory parts ID is always
between 1 and M. Optional parts ID is always greater than M.
Example:
Password must be split between one admin and four users and to recover it, admin and at least any
two of users must combine their parts. In this particular case, ExpandedScheme[n=5, m=1, k=3]
is needed. Part with ID 1 should be given to admin and the rest can be randomly distributed
between users.
Expanded Secret Sharing uses original Coda Hale's split and join operations implementations, just twice. Firstly, secret is
splited into M+1 parts, of which all are needed for reconstruction process. Parts with ID from 1 to M are the mandatory parts. Secondly, M+1 part
is splited into M-K optional parts with IDs between M+1 and K. K-M optional parts are needed to reconstruct a part from previous split.
This approach ensures that any K or more parts must include all of M mandatory parts to
retrieve the original secret.
Copyright © 2018 Balciu
Distributed under the Apache License 2.0.