When Hemi claims that its transactions can achieve "Bitcoin-level security" in 90 minutes, many people's first reaction is to question: how can a Layer 2 network inherit the security guarantees of Bitcoin's proof of work? The answer lies in Hemi's unique Proof-of-Proof consensus mechanism, a system known as PoP that is redefining how Layer 2 can leverage Layer 1's security budget.
The core logic of PoP is to publish the state root of Layer 2 to the Bitcoin main chain, but unlike traditional state anchoring solutions, Hemi introduces a dedicated PoP miner role. These miners compete to encode the Hemi block header hash into Bitcoin transactions and pay miner fees to publish to the Bitcoin network; successfully published miners will receive HEMI token rewards. This design cleverly transforms Bitcoin's PoW consensus into the finality guarantee for the Hemi network, making it exponentially costly for any attacker wanting to alter Hemi's historical state, as they would have to simultaneously attack the Bitcoin network.
From a technical implementation perspective, the PoP mechanism involves three key nodes: the Bitcoin-Secure Sequencer is responsible for producing Hemi blocks, the Bitcoin Finality Governor monitors PoP release transactions in the Bitcoin network, and PoP miners act as executors of state releases. When a new Hemi block is generated, the BSS node broadcasts the block header to the BFG nodes, and PoP miners obtain block header information from the BFG to construct Bitcoin transactions, encoding the Hemi state root in the OP_RETURN field of the transaction. Once the transaction is packaged and confirmed by the Bitcoin network, the BFG node will feedback the confirmation information to the BSS, completing the final confirmation of the Hemi block.
The brilliance of this mechanism lies in creating a closed-loop economic incentive. PoP miners need to pay Bitcoin transaction fees to publish state roots, but they can cover costs and profit through token rewards from the Hemi network. This means that the security of Hemi is directly linked to the fee market of the Bitcoin network. When congestion in the Bitcoin network leads to soaring fees, the publishing costs for PoP miners will rise, but it also means that attackers would need to pay higher fees to forge state releases. This dynamic balance naturally enhances the security of Hemi with the activity of the Bitcoin network.
Compared to other Bitcoin Layer 2 solutions, PoP exhibits significant security advantages. The joint mining model adopted by Rootstock also leverages Bitcoin's hashing power, but only about 40% of Bitcoin miners participate in joint mining, and miners can exit at any time, making Rootstock vulnerable to 51% attacks during periods of insufficient miner incentives. The Proof-of-Transfer mechanism of Stacks requires miners to burn Bitcoin to compete for block rights; although it establishes an economic link with Bitcoin, its security fundamentally depends on the value of the STX token. Once the value of the token collapses, the entire network's security budget will rapidly shrink.
Hemi's PoP is different; it anchors its security in the irreversibility of the Bitcoin main chain. Even if the price of the HEMI token drops and affects miner incentives, the Hemi state root that has been released on the Bitcoin chain is still protected by Bitcoin's PoW. This characteristic of "one release, permanent security" endows the historical state of the Hemi network with near-immutability similar to that of the Bitcoin main chain. Of course, this also means that the final confirmation time of Hemi is limited by Bitcoin's block time, and the 90-minute final confirmation window is much slower compared to Ethereum's 12 minutes or Solana's second-level confirmations.
From the perspective of application requirements, the 90-minute finality has vastly different acceptability across different scenarios. For large asset transfers or DeFi settlement scenarios, a 90-minute wait to enjoy Bitcoin-level security is an acceptable cost, representing a qualitative leap compared to the T+1 cycle of traditional interbank settlements. However, for high-frequency trading or gaming applications, a 90-minute confirmation delay would severely impact user experience. Hemi's solution is to provide a preliminary confirmation based on PoS before the final PoP confirmation, allowing applications to choose different confirmation standards based on their risk tolerance.
It is worth noting that the PoP mechanism creates new revenue sources for Bitcoin miners. As Bitcoin block rewards continue to halve, transaction fees will become the main source of income for miners, but the throughput limitations of the Bitcoin main chain mean that the ceiling of the fee market is relatively clear. Although PoP miners do not directly participate in Bitcoin block generation, their release actions contribute additional transaction fees to the Bitcoin network, which can be seen as a return of Layer 2 to the Layer 1 security budget. If more Layer 2 solutions adopt similar mechanisms in the future, the fee market of the Bitcoin network may remain active due to the prosperity of Layer 2.
Of course, the PoP mechanism also faces some potential challenges. When multiple PoP miners compete to publish the same Hemi block header simultaneously, it can lead to competition losses similar to Bitcoin orphan blocks, where miners who fail to get on-chain will lose the Bitcoin transaction fees they paid. This competitive mechanism, while ensuring decentralization of releases, may also lead to resource waste. In addition, the economic model of PoP relies on the HEMI token to keep miners sufficiently incentivized; if the token's circulating market value remains low for a long time, a decline in miner participation may extend the final confirmation time of Hemi.
From a broader perspective, PoP represents a new paradigm of "parasitic security." Traditional blockchains need to build their own consensus networks and security budgets, but PoP demonstrates how to cleverly design mechanisms to allow Layer 2 to "freeload" on the security guarantees of Layer 1. If this approach proves successful, it could inspire the birth of more innovative consensus mechanisms, allowing the security of blockchain networks to be mutually borrowed and superimposed.