Methods and systems can prove to an independent verifier that multiple activities registered on decentralized BASE network belong to the same user, without revealing true identity of the user. A selective linkability algorithm provides for linking together activities done under various of user's pseudonyms, without revealing the true user's identity. A reward calculation mechanism calculates a reward based on activities linked using the linking proof. For example, if user can prove that she already successfully completed 10 prior transactions, she might be deemed more valuable to the business making a new offer and hence eligible for a higher reward.