Libplanet Cryptographic Sortition

What is Cryptographic Sortition?

Cryptographic sortition is a technique used in decentralized systems to randomly and verifiably select participants for specific roles (e.g., block proposal or voting) in a secure and unbiased manner. Unlike traditional random selection, it allows each participant to independently determine their eligibility using private information (such as a secret key) and then prove their selection with a verifiable cryptographic proof. This method enhances scalability and security by avoiding centralized coordination and reducing communication overhead.

Algorand’s Approach

Algorand, a proof-of-stake blockchain protocol, employs cryptographic sortition using Verifiable Random Functions (VRFs) to select block proposers and committee members probabilistically based on their stake. Each participant runs a VRF locally to determine their eligibility and attaches the proof to their message. The probability of selection is proportional to the participant’s stake, and the process guarantees both unpredictability and verifiability without requiring synchronous interaction between nodes.

Practical Implementation

I implemented Algorand-style cryptographic sortition in Libplanet, a .NET-based blockchain framework, leveraging the ECVRF implementation as a foundation, to enable verifiable and stake-weighted role assignment in the consensus process. This implementation allows each participant to locally determine their eligibility for block production or consensus participation using ECVRF output and a threshold-based selection mechanism inspired by Algorand’s binomial probability model. The result includes a verifiable proof that can be validated by other nodes without compromising the participant’s private key or requiring centralized coordination. This contribution enhances Libplanet’s consensus layer by enabling fair, decentralized role assignment with minimal overhead and high security guarantees.