VerifiableSecretSharing

Verifiable Secret Sharing for Shamir Threshold Scheme

This implementation was part of the contribution for the following paper:

Bailey Kacsmar, Chelsea Komlo, Florian Kerschbaum, Ian Goldberg. "Mind the Gap: Ceremonies for Applied Secret Sharing." Proceedings on Privacy Enhancing Technologies. Vol. 2020, No. 2. 18 pages. April 2020.

This library presents a subset of the presented improvements to Shamir's threshold scheme presented in this paper. As such, this library provides the ability for participants to verify the integrity of shares received by a central dealer, and for participants to update shares in the future, providing protection against an adversary who can collect a threshold number of shares across update epochs, but not within a single epoch.

Use

Note that this library does not provide support for serialization and deserialization of shares in order to securely transmit and store shares after they have been generated. Furthermore, the caller of generate_shares will need to account for securely deleting shares once they have been properly transmitted to participants.

Furthermore, this library does not account for how participants should handle the case when a share or update is not valid.

Additional Improvements

Note that although the paper discusses additional improvements to Shamir's Threshold Scheme, we did not include all improvements in this library due the variance in implrementation requirements. For examle, when operating in Extended Mode, the integrity value can be distributed along with shares in order to allow for validating the secret document upon recovery. However, as platform and security requirements can change how documents are encrypted, we opted to not include improvements for the Extended mode of operation in this library; see the paper (Figure 5 specifically) for more details.