P2share: how to turn any network (or testnet!) into a bitcoin miner

In these systems, miners collaborate by submitting shares to a secondary chain (the sharechain), which establishes internal consensus rules for how rewards are allocated. Typically, the sharechain may select a shareholder at random or according to some deterministic mechanism to receive the next block reward, and expects miners to honor this decision in their coinbase outputs.

However, an intrinsic limitation arises from the fact that Bitcoin’s mainnet protocol remains agnostic to the rules enforced by any auxiliary sharechain. Once a miner discovers a valid Bitcoin block, they retain full discretion over the structure of its coinbase transaction. This means that while the sharechain can detect whether a submitted share (i.e., a candidate block) adheres to its own payout rules, it cannot compel Bitcoin itself to enforce those rules on-chain. If the winning miner chooses to disregard the sharechain’s selected beneficiary and instead claim the reward for themselves or another party, Bitcoin will accept the block so long as it satisfies all consensus requirements, regardless of any off-chain agreements.

This dynamic gives rise to a central incentive problem. The integrity of the reward-sharing arrangement is maintained only to the extent that miners expect continued participation and future benefit from adhering to the sharechain’s protocol. The threat of off-chain penalties—such as ostracization, slashing of share balances within the sharechain, or exclusion from future network earnings—can act as deterrents against deviation. These mechanisms rely on robust monitoring and collective enforcement; if a miner violates the agreed reward allocation, the sharechain can respond by invalidating future contributions from that miner or imposing other economic consequences within the context of the sharechain itself.

Yet, the efficacy of such off-chain penalties is inherently limited by their inability to reverse or negate mainchain transactions. A rational, short-term-oriented miner might reason that if the value of a single block’s reward outweighs the expected future revenue from honest participation, the incentive to defect becomes substantial. This is particularly true for miners with little stake in the ongoing health of the sharechain or those who operate opportunistically. As a result, the system’s overall security and fairness depend on the balance between immediate gains from defection and the present value of sustained, cooperative engagement.

Successful decentralized mining pools must therefore devise incentive structures that align long-term participation with honest behavior. This often involves mechanisms such as requiring miners to post collateral within the sharechain, distributing rewards over multiple blocks to delay full payment until good behavior is observed, or instituting reputational systems that make deviation costly in terms of future earning potential. Ultimately, the challenge lies in engineering a framework where miners’ optimal strategy is to consistently follow the sharechain’s reward allocation, even though Bitcoin itself provides no direct enforcement of these higher-level agreements.