Shared Security

What Is Shared Security?

Shared security is a design pattern where multiple blockchain networks inherit their economic security from a single, larger base chain rather than each building an independent set of validators or miners. The base chain's existing stake (or hash power) is extended to protect additional networks, giving them security guarantees that would otherwise take years and significant capital to establish independently.

The core problem shared security addresses is bootstrapping. A new proof-of-stake chain launching with a $10 million market cap can be attacked by anyone willing to acquire $5 million worth of its token. Contrast this with Ethereum, where attacking the validator set would require acquiring tens of billions of dollars in staked ETH. Shared security lets the new chain tap into Ethereum's economic weight rather than relying on its own thin market.

The concept is not new to crypto. Bitcoin's merged mining allowed Namecoin to share Bitcoin's hash power as early as 2011. What has changed is the sophistication of the models: modern shared security protocols create structured marketplaces where base-chain stakers opt into validating additional services in exchange for extra yield.

How It Works

Shared security systems generally follow a common pattern, regardless of the specific implementation:

1. A base chain establishes strong economic security through its own consensus mechanism (proof of work, proof of stake, or a hybrid)
2. Validators or miners on the base chain opt into securing one or more additional networks
3. The additional networks inherit the base chain's security guarantees because attacking them requires overcoming the same economic threshold as attacking the base chain
4. Validators earn additional rewards (fees, token emissions) from the secured networks in exchange for their service
5. Misbehavior on the additional networks triggers penalties (slashing, loss of block rewards) enforced by the base chain

The key insight is that economic security is not consumed when shared: a validator staking $1 million on the base chain can simultaneously secure multiple additional networks without staking additional capital. The deterrent works because the same stake is at risk across all secured networks.

The Bootstrapping Problem

Every new blockchain faces a circular dependency. Users and applications need confidence that the network is secure before committing capital. But the network cannot become secure without enough staked capital or hash power, which only comes from users who believe in the network's future.

For proof-of-stake chains, this translates directly to economic vulnerability. If the total staked value is low, the cost to acquire a majority stake and mount a 51% attack is correspondingly low. An attacker could double-spend, censor transactions, or halt the chain entirely.

Shared security breaks this cycle by letting new chains rent established security rather than building it from zero. A parachain on Polkadot or a consumer chain on Cosmos does not need to convince independent validators to stake millions on its unproven token: it inherits security from the base chain's existing validator set.

Security Inheritance vs. Security Leasing

Shared security implementations fall into two broad categories:

• Full inheritance: the child chain uses the exact same validator set as the base chain. Polkadot parachains and Cosmos replicated security follow this model. The child chain cannot be attacked independently of the base chain.
• Opt-in leasing: validators individually choose which additional services to secure. EigenLayer and Babylon follow this model. Security levels vary depending on how much stake opts in to each service.

Major Implementations

Polkadot Relay Chain

Polkadot pioneered structured shared security with its relay chain architecture. The relay chain acts as a central security hub, and parachains (parallel chains) connect to it through slot auctions. All parachains share the relay chain's full validator set: validators are randomly assigned to verify parachain blocks in each epoch.

In 2024, Polkadot transitioned from the slot auction model to "Agile Coretime," where teams purchase blockspace on demand rather than leasing a full slot for up to two years. This lowered the barrier to entry: instead of locking millions of DOT to win an auction, projects can buy coretime in smaller increments.

The trade-off is sovereignty. Parachains must conform to Polkadot's block format and validation rules. They gain strong security but lose the flexibility of running a fully independent chain.

Cosmos Interchain Security

Cosmos took a different approach with Interchain Security (ICS), launched in 2023. Rather than a single relay chain, Cosmos uses a hub-and-spoke model where the Cosmos Hub's ATOM validators can opt into securing additional "consumer chains."

The initial version (Replicated Security) required the full Cosmos Hub validator set to validate every consumer chain. This was later refined into Partial Set Security (PSS), where only a subset of validators needs to opt in. PSS gives consumer chains more flexibility: they can set a minimum participation threshold (for example, requiring the top 100 validators by stake to participate) while allowing others to join voluntarily.

Consumer chains pay the Cosmos Hub validators through a share of their transaction fees and block rewards. This creates a direct economic relationship: validators earn yield for the additional validation work, and consumer chains get security they could not afford independently.

EigenLayer and Restaking

EigenLayer introduced restaking on Ethereum, allowing stakers to extend their staked ETH to secure additional services called Actively Validated Services (AVSs). Launched on Ethereum mainnet in 2024, EigenLayer created a marketplace where ETH stakers can opt into securing oracles, bridges, data availability layers, and other infrastructure.

The mechanism works through smart contracts that impose additional slashing conditions on restaked ETH. If a validator misbehaves while operating an AVS, their restaked ETH can be slashed according to the AVS's rules. This gives AVSs cryptoeconomic security proportional to the amount of ETH restaked to them.

Liquid restaking protocols like EtherFi and Renzo wrap restaked positions into tradeable tokens, adding a layer of composability. However, this also introduces rehypothecation risk: the same ETH can be pledged to multiple AVSs simultaneously, amplifying the impact of any slashing event.

For a deeper analysis of restaking risks, see the research article on EigenLayer restaking risks.

Babylon Protocol and Bitcoin Staking

Babylon brings shared security to Bitcoin by enabling native Bitcoin staking without bridges or wrapped tokens. BTC holders lock their Bitcoin in special scripts on the Bitcoin L1, and these locked funds serve as economic collateral for securing external proof-of-stake chains.

Babylon's design uses Bitcoin's native scripting capabilities: timelocks enforce lock-up periods, and a cryptographic trick called "extractable one-time signatures" enables slashing. If a validator signs conflicting blocks on a consumer chain, anyone can extract the validator's private key from the two conflicting signatures and claim their locked BTC.

For more on how Bitcoin staking works, see the research on Bitcoin restaking with Babylon and Lombard.

Merged Mining

Merged mining is the oldest form of shared security in crypto, dating back to Namecoin in 2011. It allows proof-of-work miners to submit the same hash computation to multiple chains simultaneously. The child chain accepts the parent chain's proof of work as valid, inheriting its hash rate without requiring miners to perform additional computation.

RSK (Rootstock) is the most prominent merged-mined chain today, with over 50% of Bitcoin's hash power contributing to its security. However, merged mining has limitations: it only works for proof-of-work chains, and miners can choose to attack the child chain without risking their position on the parent chain (since there is no slashing in PoW).

The Economic Model

Shared security creates a marketplace for economic security. On the supply side, base-chain stakers offer their capital as collateral. On the demand side, new networks purchase security by paying fees or sharing revenue.

For stakers, the appeal is additional yield. An ETH staker earning 3-4% from Ethereum validation can earn supplemental returns by opting into AVSs through EigenLayer. Cosmos Hub validators earn consumer chain fees on top of their ATOM staking rewards. This turns staked capital into a productive asset that generates returns from multiple sources.

For new networks, the appeal is cost efficiency. Building an independent validator set requires distributing a native token, incentivizing stakers with high emission rates (which causes inflation), and waiting months or years for sufficient economic weight to accumulate. Renting security from an established chain is faster and often cheaper.

The economic dynamics create a flywheel: more stakers opting into shared security increases the total security available, which attracts more networks, which generates more fees, which attracts more stakers. This concentration effect is what makes shared security protocols potential winner-take-most markets.

How Spark Inherits Bitcoin's Security

Spark takes a distinct approach to shared security through its statechain architecture. Rather than using staking or merged mining, Spark anchors its off-chain virtual UTXOs directly to Bitcoin's UTXO set. Every Spark balance is backed by a real Bitcoin UTXO on the base layer, and users retain the ability to exit to Bitcoin L1 unilaterally at any time.

This design means Spark does not need to bootstrap its own validator economics. The security guarantee comes from Bitcoin's proof-of-work consensus directly: the same hash power that protects Bitcoin transactions protects the on-chain anchors of Spark balances. A user's funds can always be recovered on Bitcoin L1, regardless of what happens to the Spark network.

For a deeper look at how this architecture works, see the Spark Bitcoin Layer 2 overview and the statechain scaling deep dive.

Use Cases

New Layer 1 Chains

The most direct use case for shared security is new layer 1 blockchains that lack the network effects to attract independent validators. Instead of launching with low-security economics and hoping to grow, they can inherit security from day one. Cosmos consumer chains like Neutron and Stride adopted this path rather than building independent validator sets.

Middleware and Infrastructure

Oracles, bridges, and data availability layers need cryptoeconomic guarantees but are not full blockchains. EigenLayer's AVS model fits this category: services like EigenDA (data availability) and cross-chain messaging protocols use restaked ETH for security without running their own chains.

Application-Specific Chains

App-chains that serve a single application (a DEX, a game, a social network) benefit enormously from shared security. They need custom execution environments but cannot justify the cost of an independent validator set for a single application. Shared security lets them focus on their application logic while outsourcing economic protection.

Bitcoin Layer 2 Networks

Bitcoin layer 2 protocols inherit Bitcoin's security through various mechanisms: merged mining for RSK, statechains for Spark, and federated pegs for Liquid. Each makes different trade-offs between the degree of security inherited and the trust assumptions introduced.

Risks and Considerations

Slashing Cascades

When the same stake secures multiple services, a slashing event on one service can reduce the security of all others. If a validator has $10 million in restaked ETH across five AVSs and gets slashed on one, the remaining four lose a portion of their security backing. In extreme cases, this could trigger a cascade where reduced security on one service makes attacking it cheaper, leading to further slashing events.

Correlated Failures

Shared validator sets introduce correlated risk. If the same operators run validation software for multiple networks, a bug in shared infrastructure (operating system, cloud provider, client software) can take down all secured networks simultaneously. Independent chains with diverse validator sets are more resilient to this type of failure.

Concentration and Centralization

Shared security can centralize power in the hands of the largest stakers. On EigenLayer, for example, the biggest ETH stakers have the most capacity to secure AVSs and earn additional yield. Smaller stakers may be priced out of participation, leading to a concentration of validation power that undermines the decentralization the base chain was designed to provide.

Complexity and Attack Surface

Each additional service a validator secures adds software to run, protocols to understand, and potential vulnerabilities to monitor. Validators may take on more services than they can effectively operate, increasing the risk of misconfiguration or downtime. The smart contracts that govern restaking and slashing are themselves potential attack vectors: a bug in a slashing contract could lead to unjust penalties or, worse, allow an attacker to drain staked funds.

Economic Sustainability

The yield that attracts stakers to shared security must come from somewhere. If consumer chains or AVSs cannot generate enough fee revenue to pay validators, the model relies on token emissions, which creates inflationary pressure. Long-term sustainability depends on real demand for the services being secured, not just speculative staking yield.

Shared Security Comparison

This glossary entry is for informational purposes only and does not constitute financial or investment advice. Always do your own research before using any protocol or technology.