Proactive Secret Sharing
If the players store their shares on insecure computer servers, an attacker could crack in and steal the shares. If it is not practical to change the secret, the uncompromised (Shamir-style) shares can be renewed. The dealer generates a new random polynomial with constant term zero and calculates for each remaining player a new ordered pair, where the x-coordinates of the old and new pairs are the same. Each player then adds the old and new y-coordinates to each other and keeps the result as the new y-coordinate of the secret.
All of the non-updated shares the attacker accumulated become useless. An attacker can only recover the secret if he can find enough other non-updated shares to reach the threshold. This situation should not happen because the players deleted their old shares. Additionally, an attacker cannot recover any information about the original secret from the update files because they contain only random information.
The dealer can change the threshold number while distributing updates, but must always remain vigilant of players keeping expired shares.
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Famous quotes containing the words secret and/or sharing:
“A man’s true merit ‘tis not hard to find;
But each man’s secret standard in his mind,
That casting-weight pride adds to emptiness,
This, who can gratify, for who can guess?”
—Alexander Pope (1688–1744)
“... probably all of the women in this book are working to make part of the same quilt to keep us from freezing to death in a world that grows harsher and bleaker—where male is the norm and the ideal human being is hard, violent and cold: a macho rock. Every woman who makes of her living something strong and good is sharing bread with us.”
—Marge Piercy (b. 1936)