The Bitcoin Security Budget Issue
The Bitcoin security budget issue refers to the long-term sustainability of the network's security, which is primarily funded by block rewards and transaction fees paid to miners
1. As the block subsidy (the number of new bitcoins created per block) decreases over time due to halving events, the network must rely increasingly on transaction fees to incentivize miners to secure the blockchain against attacks
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The security budget is defined as the cost required to marshal 100% of the hash rate, which is the cost an attacker would need to pay to execute a 51% attack
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Core Concerns of the Security Budget
The primary concern is that a declining proportional security spending, which is a function of Bitcoin's declining inflation rate, could lead to a declining proportional hash rate intensity
4. If the total revenue earned by miners (the security budget) becomes too low, the cost of executing a 51% attack could drop to a point where it becomes economically feasible for an attacker
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The Threat of a 51% Attack
A 51% attack occurs when an attacker controls the majority of the network's hash rate, allowing them to reorganize the blockchain and execute a double-spend attack
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- Double-Spend Attack: An attacker could send Bitcoin to an exchange, withdraw the equivalent fiat currency, and then reorganize the chain to reverse the original sending transaction. If successful, the attacker would end up with both the Bitcoin and the fiat 3.
- Confirmation Counterargument: A common counterargument suggests that users and exchanges could simply wait for more block confirmations (e.g., 60 instead of the current 6) to significantly decrease the chances of a double-spend attack 3.
- Flaw in the Counterargument: This counterargument fails if the attacker can afford the entire security budget. If the attack is sustained, it is considered a flow, not a stock, and the attack may never end. Honest miners, realizing they are losing the hash war, might turn off their rigs, causing the security budget and the cost to attack to drop to zero 3.
Factors Impacting the Security Budget
1. Miner Revenue from Transaction Fees
The security budget is directly tied to miner revenue. Recent trends, such as the rise of ordinals and inscriptions, have positively impacted this revenue
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- Increased Fees: Inscriptions have contributed between 15% and 30% of the total transaction fee revenue for miners 1.
- Blockspace Demand: Inscription transactions account for about half of all Bitcoin transactions, paying a meaningful proportion of fees 1.
- Positive Impact: If this trend persists, the improved miner economics could positively impact Bitcoin's security budget, especially amid the fast-approaching halving events, leading to higher Bitcoin security in absolute terms 1.
2. Security as a Percentage of Market Capitalization
Historically, Bitcoin's security spending as a percentage of its market capitalization has been declining
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3. External Solutions and Shared Security
New protocols are being developed to leverage Bitcoin's security budget for other ecosystems
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- Babylon Staking: The Babylon system aims to enable Bitcoin shared security via staking 5. This mechanism allows staked Bitcoin to be held in a self-custodial vault with a time-lock on the Bitcoin Mainnet 5.
- Cross-Chain Security: Babylon acts as a bridge to transfer security benefits and facilitate communication among multiple blockchain systems, using Bitcoin as the universal "source of truth" through timestamping 5.
- DeFi Integration: Other projects are exploring ways to use Bitcoin Layer 1 holdings to represent voting power in DeFi protocols on other chains, leveraging Bitcoin's massive security budget to influence decisions across ecosystems 6.
The relationship between security supply and demand is critical, where an increase in the demand for security must be met by a higher supply, often requiring a price increase to incentivize securing the network
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