zk-nullifier

For non zk applications see this skill to use nullifiers: skills/payments

A nullifier is a deterministically derived hash to ensure an action can only be performed once. The nullifier cannot be linked to the action or user. For example Zcash uses nullifiers to prevent double spending.

To implement nullifiers we need a data structure that ensures every nullifier is only created once and never deleted. On Solana a straight forward way to implement nullifiers is to create a PDA account with the nullifier as seed.

For custom ZK Solana programs and privacy-preserving applications to prevent double spending. Guide to integrate rent-free nullifier PDAs for double-spend prevention. Source: lightprotocol/skills.