Proof-of-Stake (PoS) Bridge

The bridge's security is directly tied to a set of validators who must stake the native token of the PoS chain (e.g., ATOM, MATIC, SOL) as collateral. This economic stake is subject to slashing—a penalty where a portion of the validator's stake is burned—for malicious behavior like signing invalid cross-chain messages. This creates a strong financial disincentive against attacks.

Unlike bridges relying on multi-signature wallets, a PoS bridge inherits the finality guarantees of its underlying blockchain. Once a block containing a bridge transaction is finalized by the PoS consensus (e.g., Tendermint BFT, Gasper), the transaction is considered irreversible. This provides strong, cryptographic assurance that validated cross-chain state transitions are permanent and secure.

Key bridge parameters—such as the validator set, staking requirements, and supported assets—are typically managed via on-chain governance. Token holders vote on proposals to upgrade bridge contracts, add new chains, or modify security models. This contrasts with centrally administered bridges and aligns the bridge's evolution with its stakeholder community.

A decentralized network of relayers (often the validators themselves) monitors events on connected chains. They submit transaction proofs and are rewarded with bridge fees for honest service. Their role is distinct from validation; they are message carriers, while validators are the signers/approvers. This separation can optimize for efficiency and cost.

The bridge's operation is deeply integrated with its host chain's native token. This token is used for:

• Staking by validators for security.
• Paying transaction fees for bridge operations.
• Governance voting on bridge parameters. This creates a synergistic relationship where the utility and security of the bridge enhance the value of the underlying PoS ecosystem.

The primary trust assumption is in the honest majority of the validator set's staked value. The main attack vector is a long-range attack or liveness attack on the underlying PoS chain. If malicious actors gain control of >1/3 (for liveness) or >2/3 (for safety) of the total stake, they could compromise the bridge. Security is therefore a function of the chain's total value staked and validator decentralization.

A theoretical flaw where validators have minimal cost to validate multiple, potentially conflicting, blockchain histories. This can undermine consensus finality. In practice, this is mitigated by slashing penalties that destroy a validator's staked assets for provably malicious behavior, such as double-signing blocks.

An attack where an adversary acquires private keys from validators that staked in the distant past (when stake was cheap) to rewrite history from an earlier point. Defenses include:

• Checkpointing: Hard-coding recent block hashes as immutable.
• Subjectivity Periods: Requiring new nodes to trust a recent, verified state from a reputable source.

Security depends on a decentralized set of validators. Risks include:

• Stake Pool Dominance: A few large staking pools or exchanges controlling a majority of stake, enabling censorship or chain halts.
• Geographic/Infrastructure Concentration: Validators relying on the same cloud providers or jurisdictions, creating a single point of failure.
• Wealth Concentration: The "rich get richer" effect, where large stakeholders earn more rewards, potentially increasing centralization over time.

The security budget is the total value of assets staked and subject to slashing. Key metrics:

• Staking Ratio: The percentage of the native token's supply that is staked. A low ratio means lower economic security.
• Slashing Conditions: Clearly defined, algorithmically enforced penalties for downtime, double-signing, or other protocol violations are critical for deterrence.

Liquid staking tokens (e.g., stETH, cbETH) allow staked assets to be used elsewhere in DeFi. This introduces systemic risk:

• If the derivative depegs from the underlying staked asset, it can cause cascading liquidations.
• Rehypothecation: The same economic value backing the derivative may be used as collateral in multiple protocols simultaneously, creating leverage and contagion risk.

In PoS chains where governance power is derived from stake, an attacker could:

• Acquire enough tokens to pass malicious governance proposals.
• Use proposals to disable slashing, alter validator rewards, or siphon funds from the community treasury.
• This turns economic majority into governance majority, a key difference from Proof-of-Work systems.