What is a Secret Sharing Scheme?
In cryptography, secret sharing schemes are schemes that split shares of a given secret among a set of trusted recipients. For example, this secret might be a very important piece of information that is needed in the future, but meanwhile needs to be kept private and secure. Each share is completely useless on its own, but when combined, the shares reconstruct and display the secret. As a thought experiment: think of secret sharing schemes as a puzzle where the puzzle pieces are split among ten players but are completely blank. The image that the puzzle can create only appears once all the pieces are put together.
Why is Secret Sharing needed?
The kind of data that is best suited for a secret sharing algorithm is information that must be kept absolutely private, but must also be stored securely and never lost. Typically, you'd use secret sharing for access keys to accounts with highly sensitive information in them. The goal is to spread the key out from one geographic location into multiple — so that in order to compromise a system, you'd first need to compromise devices in several distinct locations. There are multiple kinds of secret sharing algorithms: the one we'll be discussing is Shamir's Secret Sharing (SSS).
What is Shamir's Secret Sharing?
Adi Shamir's scheme is a securely encrypted secret sharing scheme that requires some or all participants to reconstruct a secret. Shamir's Secret Sharing allows for a hierarchical schema where some participants may be more trustworthy than another. For example; when running Shamir's scheme for a private key and sharing it among friends and family, one could grant family members greater authority in the scheme and friends lesser authority in the scheme.
How does Vault12 use Shamir's Secret Sharing?
In Part 1 of the video below, well-known security expert Terence Spies explains how the fundamentals of Shamir's Secret Sharing operate, and how its cryptography is used in the Vault12 system.
Part 1: The Cryptography behind Vault12 with Terence Spies
Part 2 of the video explains how advanced concepts such as Thresholds work to give Vault12 a streamlined experience.
Part 2: The Cryptography behind Vault12 with Terence Spies
What is the importance of Shamir's threshold number of shares?
Considering the nature of how Shamir's scheme is built, a threshold parameter can be specified during the creation of the scheme. Instead of requiring that every single share is present to reconstruct a key like a puzzle, Shamir's scheme requires a threshold number of shares. The value of this threshold is at the discretion of the secret sharer. The secret sharer could choose to require every single share for reconstruction of the key or three-quarters of all shares held by participants.
Shamir's Secret Sharing allows your secrets to be both Secure and Dynamic
Shamir's Secret Sharing has the following properties:
- Secure: Shamir's scheme is cryptanalytically unbreakable in its
encryption model in that no holder of a share can uncover the shared
secret without first gaining access to the threshold number of secret
shares. The secret will be kept absolutely secure and confidential from
participants in the scheme. Only the secret sharer will see the original
data from the deconstruction and reconstruction of the data.
- Dynamic: The scheme allows for a secret owner to amend the rules of a given secret securely. This means a person sharing a secret among a set of participants could use their status as the secret owner to create more splits of a key and distribute those to more participants if he or she so chose. Or, the secret owner could remove some participants remotely from the scheme — all while leaving the other participants in the secret sharing scheme completely unaffected.
With such properties, Shamir's Secret Sharing could have a wide array of use cases for the preservation of sensitive data. General examples include the secure and private preservation of private keys or passwords, and images of sensitive balance restoration keys.
Should you decentralize custody of your secrets?
Using an application built on Shamir's Secret Sharing doesn't imply that it's the perfect layer of security for the storage of all secrets in all cases — rather, it responds to a specific situation that is suitable for decentralized and trusted custody of a specific secret.
At Vault12, we think that the best-suited specific secrets for which to utilize Shamir's Secret Sharing are private keys to cryptocurrency balances, and seed phrases for the recovery of wallets. To that end, Vault12's mobile app implementation of Shamir's Secret Sharing - Vault12 Guard - lets users assign friends and family as guardians of their secrets.
Shamir's Secret Sharing is an intriguing cryptography scheme that is useful for decentralizing custody of sensitive data. However, it is not suited for the maintenance of just any secretive data. Since the scheme entails assigning participants to store shares of a secret, these participants need to be trusted. While the encryption scheme renders it impossible for participants to derive anything from the share they receive, multiple participants could collude together to meet the threshold requirement of shares and uncover that secret. Therefore, it is important that the people that you share a secret with using Shamir's Secret Sharing are trustworthy.
For more details about Vault12's innovative technologies, visit the Vault12 Technology page.
