Security Model

The core protocol that enables network participants (nodes) to agree on the state of the ledger without a central authority. It defines the rules for block creation and validation.

• Proof of Work (PoW): Uses computational puzzles; security is tied to energy expenditure (e.g., Bitcoin).
• Proof of Stake (PoS): Uses staked capital; security is tied to economic penalties (e.g., Ethereum).

The mathematical functions that guarantee data integrity, authentication, and privacy. These are the unbreakable building blocks of trust.

• Hash Functions (e.g., SHA-256): Create unique, deterministic fingerprints of data.
• Digital Signatures (e.g., ECDSA): Prove ownership and authorize transactions without revealing the private key.
• Zero-Knowledge Proofs: Enable verification of a statement's truth without revealing the underlying data.

A system of rewards and punishments that aligns the financial interests of participants with network security. This is the "skin in the game" principle.

• Block Rewards & Fees: Compensate validators/miners for honest participation.
• Slashing: The automatic confiscation of a validator's staked funds for provable malicious behavior (e.g., double-signing).

The network's resilience to component failures or malicious actors, and the guarantee that a confirmed transaction cannot be reversed.

• Byzantine Fault Tolerance (BFT): The ability to reach consensus despite some nodes acting arbitrarily or maliciously.
• Probabilistic Finality: Common in PoW; confidence in a block increases as more blocks are built on top of it.
• Absolute Finality: Common in BFT-based PoS; a block is irreversibly finalized after a voting round.

The explicit or implicit conditions under which the security model is considered valid. These define the "trust boundary."

• Trustlessness: No single entity needs to be trusted; security is derived from code and cryptography.
• Trusted Setup: A one-time ceremony where initial parameters must be generated honestly (e.g., some zk-SNARK circuits).
• Honest Majority: The model assumes that a majority (e.g., >50% of hash power or stake) is acting honestly.

The specific threats the model is designed to resist and the countermeasures in place. A robust model is defined by what it can withstand.

• 51% Attack: Controlling a majority of resources to rewrite history. Mitigated by making acquisition prohibitively expensive.
• Sybil Attack: Creating many fake identities. Mitigated by requiring costly resources (hash power, stake) for participation.
• Long-Range Attack: Rewriting history from an early block. Mitigated by checkpoints or finality gadgets.

This model relies on a network of independent node operators who must reach consensus on the correct data point before it is reported on-chain. Security is derived from the economic cost of corrupting a majority of the network, similar to a blockchain's own consensus. Key mechanisms include:

• Multi-signature reporting where a threshold of signatures is required.
• Aggregation functions (e.g., median) to filter out outliers.
• Staking and slashing to penalize malicious or faulty nodes.

Node operators are required to stake a bond of the network's native token. Correct performance earns rewards and builds reputation, while provably malicious or unreliable data submission results in slashing (loss of stake). This creates a strong cryptoeconomic security layer where the cost of attack is quantifiable and the penalty for failure is severe. Reputation scores often determine node selection and reward distribution.

Security is enhanced by aggregating data from multiple, independent primary sources (e.g., multiple centralized exchanges for a price feed). This prevents a single point of failure or manipulation at the source level. Networks implement:

• Source attestations to prove data provenance.
• Statistical outlier detection to discard anomalous reports.
• Fallback mechanisms to switch sources if one becomes unavailable or untrustworthy.

Data integrity is secured through cryptographic proofs that verify the data's origin and that it hasn't been tampered with. Common techniques include:

• Transport Layer Security (TLS) proofs to authenticate API calls from primary sources.
• Commit-Reveal schemes to prevent front-running and data manipulation by the oracle itself.
• Zero-knowledge proofs (ZKPs) to allow nodes to prove correct computation without revealing sensitive source data.

The protocol that ensures all network participants agree on the state of the ledger. It is the foundation of trust in a decentralized system.

• Proof of Work (PoW): Security is derived from the immense computational energy required to mine blocks, making attacks prohibitively expensive.
• Proof of Stake (PoS): Security is derived from the economic value (staked assets) that validators risk if they act maliciously.
• Byzantine Fault Tolerance (BFT): Security is derived from a known set of validators who must reach a supermajority agreement on each block.

The mathematical functions that secure data and identities on-chain. A failure here is a fundamental breach.

• Hash Functions (SHA-256, Keccak): Create unique, irreversible fingerprints of data. A collision (two inputs with the same hash) would break blockchain integrity.
• Digital Signatures (ECDSA, EdDSA): Prove ownership of a private key without revealing it. Security relies on the computational infeasibility of deriving the private key from the public key.
• Zero-Knowledge Proofs (ZKPs): Allow one party to prove a statement is true without revealing the underlying data, enhancing privacy and scalability.

The incentive structure designed to make honest behavior more profitable than attacking the network.

• Staking Slashing: In PoS, validators have a portion of their staked assets destroyed for malicious actions like double-signing.
• Transaction Fees: Paid to validators/miners, these fees secure the network by rewarding honest block production.
• Cost of Attack: The model ensures the cost to execute a 51% attack or other consensus attacks far outweighs any potential profit, making it economically irrational.

Flaws in the code of decentralized applications (dApps) that run on the blockchain, representing a major attack surface.

• Reentrancy: A function that makes an external call before updating its state can be recursively called to drain funds.
• Oracle Manipulation: Dependence on a single, corruptible data feed can lead to incorrect contract execution and financial loss.
• Integer Overflow/Underflow: Incorrect arithmetic can wrap values, allowing unexpected state changes.
• Access Control: Missing or incorrect permission checks can let unauthorized users execute critical functions.

Attacks targeting the underlying peer-to-peer network or the software clients that nodes run.

• Sybil Attack: An attacker creates many fake identities (nodes) to gain disproportionate influence over the network.
• Eclipse Attack: Isolating a specific node from the honest network to feed it a false view of the blockchain.
• Denial-of-Service (DoS): Overwhelming a node or the network with traffic or computationally expensive transactions to halt operations.
• Client Diversity: Reliance on a single client implementation creates systemic risk; a bug could take down the entire network.

The security of the endpoints—user wallets and private keys—which are often the weakest link.

• Private Key Compromise: Loss or theft of a private key means irrevocable loss of assets. Secure storage (hardware wallets, multi-sig) is critical.
• Phishing & Scams: Users are tricked into signing malicious transactions or revealing seed phrases.
• Supply Chain Attacks: Malicious code is injected into a trusted library, wallet software, or developer tool.
• Front-running: Miners/validators exploit their ability to order transactions for profit, a market integrity issue.

The study and application of economic incentives, cryptography, and game theory to secure decentralized systems. It aligns rational participant behavior with network security goals.

• Incentives: Block rewards and transaction fees for honest validation.
• Penalties (Slashing): Financial penalties for malicious or lazy behavior in PoS systems.
• Game Theory: Designing systems where the most profitable strategy is to follow the protocol honestly.

Specific methods by which adversaries attempt to compromise a blockchain's security model. Understanding these is key to evaluating a chain's resilience.

• 51% Attack: Controlling majority hash power (PoW) or stake (PoS) to rewrite history.
• Sybil Attack: Creating many fake identities to gain undue influence.
• Long-Range Attack: Creating an alternative chain from a point far back in history (a risk for some PoS chains).
• Reorg (Reorganization): A shorter chain outcompeting the canonical chain, potentially reversing transactions.

The explicit or implicit dependencies on specific entities or conditions for the system to remain secure. Lower trust assumptions generally mean higher decentralization.

• Trustless: Security relies solely on code and cryptography (e.g., Bitcoin settlement).
• Trust-Minimized: Reduces but doesn't eliminate trust, often via economic stakes (e.g., Ethereum PoS).
• Federated/Consortium: Security depends on a pre-selected, known group of validators.

The irreversible confirmation that a block and its transactions are permanently part of the canonical chain. Different security models provide different finality guarantees.

• Probabilistic Finality: Likelihood of reversion decreases with more confirmations (PoW).
• Absolute (Instant) Finality: Guaranteed irreversibility after a consensus round (common in BFT-style PoS).
• Economic Finality: Reversal is theoretically possible but prohibitively expensive due to slashing.

The group of participants responsible for proposing and attesting to blocks. Its size, selection process, and entry requirements are critical to the security model.

• Permissionless: Anyone can join by providing resources (PoW hash power or PoS stake).
• Permissioned: Entry is controlled by a central authority or consortium.
• Decentralization: A larger, more geographically distributed validator set increases censorship resistance and reduces collusion risk.