P2P Network

The core principle where control and data are distributed across all participants instead of a central server. This eliminates single points of failure and censorship.

• No Central Authority: No single entity controls the network or can unilaterally alter data.
• Fault Tolerance: The network remains operational even if many nodes fail.
• Example: Bitcoin's blockchain is maintained by thousands of independent nodes worldwide.

Peers contribute their own resources—such as bandwidth, storage, and compute power—to the collective operation of the network.

• Shared Workload: Tasks like data storage (Filecoin, BitTorrent) or transaction validation (blockchain nodes) are distributed.
• Incentive Models: Many networks use cryptoeconomic incentives (e.g., block rewards, storage fees) to encourage resource contribution.
• Contrast: Unlike client-server models where servers bear all costs.

The protocols that enable distributed peers to agree on the state of a shared ledger or dataset without a central coordinator. This is critical for blockchain-based P2P networks.

• Purpose: Achieves Byzantine Fault Tolerance in an untrusted environment.
• Common Types: Proof of Work (Bitcoin), Proof of Stake (Ethereum, Cardano), and Practical Byzantine Fault Tolerance (Hyperledger Fabric).
• Process: Nodes follow a predefined set of rules to validate and order transactions.

The methods by which nodes find and communicate with each other to form and maintain the network overlay.

• Bootstrapping: New nodes connect to the network via known bootstrap nodes or a seed list.
• Distributed Hash Tables (DHT): A common system (used by BitTorrent, IPFS) for efficiently locating data and peers across the network.
• Gossip Protocols: Peers periodically exchange information with neighbors to propagate data, ensuring eventual consistency.

Ensuring data cannot be altered once validated and agreed upon by the network, a hallmark of blockchain P2P systems.

• Cryptographic Hashing: Each block contains a hash of the previous block, creating a cryptographically-secured chain.
• Tamper-Evidence: Altering any past data would require recomputing all subsequent hashes, which is computationally infeasible on a well-secured network.
• Auditability: Provides a permanent, verifiable record of all transactions.

The network's inherent ability to resist control, shutdown, or content filtering by any single party or government.

• Architectural Property: Stemming directly from decentralization and a globally distributed node set.
• Permissionless Participation: Anyone can join the network as a peer, validator, or user without approval.
• Key Use Case: Enables decentralized finance (DeFi) and uncensorable communication platforms.

An attack where a single adversary creates many fake identities (Sybil nodes) to subvert the network's reputation or consensus system. In a P2P network, this can lead to eclipse attacks (isolating a node), spam, or influencing gossip protocol message propagation. Defenses include Proof-of-Work, Proof-of-Stake, or resource-based admission to make identity creation costly.

A targeted attack where an adversary monopolizes all incoming and outgoing connections of a victim node, isolating it from the honest network. The attacker can then:

• Feed the victim a false view of the blockchain state.
• Enable double-spend attempts.
• Censor transactions. Countermeasures include increasing the number of outbound connections and using hardcoded seed nodes or a random peer selection algorithm.

P2P nodes are vulnerable to DoS attacks aimed at consuming bandwidth, CPU, or memory. Attackers can flood the network with invalid transactions, spam blocks, or connection requests. Key mitigations involve:

• Rate limiting incoming connections and messages.
• Resource prioritization (e.g., mempool limits).
• Peer scoring to ban malicious nodes.
• Client diversity to prevent single-point-of-failure attacks.

When the P2P network fragments into isolated sub-networks due to internet outages or malicious routing attacks. This can cause temporary chain forks and consensus failures. Networks rely on eventual consistency and longest-chain rules to heal. However, prolonged splits risk reorgs and double-spends. Robust peer discovery and geographically distributed nodes improve resilience.

The P2P gossip protocol inherently leaks metadata. Observers can analyze IP addresses, connection graphs, and transaction propagation timing to:

• De-anonymize users and link transactions to IPs.
• Infer network topology.
• Identify mining pools or large stakeholders. Solutions include Dandelion++ for transaction propagation obfuscation, Tor/VPN support, and peer-to-peer mixing networks.

The initial process of discovering peers (bootstrapping) is a critical trust point. Nodes typically connect to hardcoded DNS seeds or use a peer discovery protocol (like Kademlia DHT). If these bootstrap mechanisms are compromised, a node could be connected to a malicious network from the start. This highlights the reliance on cryptographically verified genesis blocks and client software integrity.

The protocol that ensures all nodes in a decentralized network agree on the state of the ledger. It is the core rule-set that prevents double-spending and maintains network security.

• Proof of Work (PoW): Used by Bitcoin. Nodes (miners) compete to solve cryptographic puzzles to add a block.
• Proof of Stake (PoS): Used by Ethereum. Validators are chosen to propose blocks based on the amount of cryptocurrency they "stake" as collateral.
• Practical Byzantine Fault Tolerance (PBFT): Used in many permissioned networks. Nodes vote in multiple rounds to achieve consensus.

The method by which nodes in a P2P network propagate information. When a node receives new data (e.g., a transaction), it forwards it to a subset of its connected peers, who then forward it further, causing the data to rapidly spread across the entire network.

• Key Properties: Robust, fault-tolerant, and efficient in distributing data without a central coordinator.
• Example: Bitcoin nodes use a gossip protocol to broadcast new transactions and blocks.

The distribution of control and data across a network of independent nodes, rather than a central authority. In a P2P context, it has three key dimensions:

• Architectural Decentralization: How many physical computers make up the system.
• Political Decentralization: How many individuals or organizations control those computers.
• Logical Decentralization: Whether the system presents as a single monolithic object or a swarm (a blockchain is logically centralized).

A security threat where a single adversary creates and controls a large number of fake identities (Sybil nodes) to subvert the network's reputation or consensus system.

• Defense Mechanisms: Consensus mechanisms like Proof of Work and Proof of Stake are designed to be Sybil-resistant by making identity creation computationally or economically expensive.
• Vulnerability: Networks that rely on simple node counts for trust are highly susceptible.

The time delay in transmitting a data packet across the P2P network. High latency impacts the speed of consensus and the overall performance of the blockchain.

• Impact on Consensus: In Proof of Work, high latency can increase the rate of stale blocks (orphaned blocks). In Proof of Stake, it can affect validator coordination.
• Optimizations: Networks use techniques like block propagation optimizations (e.g., Compact Blocks in Bitcoin) and strategically placed nodes to reduce latency.