Secret Sharing - Other Uses and Applications

Other Uses and Applications

A secret sharing scheme can secure a secret over multiple servers and remain recoverable despite multiple server failures. The dealer may treat himself as several distinct participants, distributing the shares between himself. Each share may be stored on a different server, but the dealer can recover the secret even if several servers break down as long as he can recover at least t shares; however, crackers that break into one server would still not know the secret as long as fewer than t shares are stored on each server.

This is one of the major concepts behind the Vanish computer project at the University of Washington, where a random key is used to encrypt data, and the key is distributed as a secret across several nodes in a P2P network. In order to decrypt the message, at least t nodes on the network must be accessible; the principle for this particular project being that the number of secret-sharing nodes on the network will decrease naturally over time, therefore causing the secret to eventually vanish. However, the network is vulnerable to a Sybil attack, thus making Vanish insecure.

A dealer could send t shares, all of which are necessary to recover the original secret, to a single recipient. An attacker would have to intercept all t shares to recover the secret, a task which is more difficult than intercepting a single file, especially if the shares are sent using different media (e.g. some over the Internet, some mailed on CDs).

For large secrets, it may be more efficient to encrypt the secret and then distribute the key using secret sharing.

Secret sharing is an important primitive in several protocols for secure multiparty computation.