Practical Byzantine Fault Tolerance (PBFT) is designed for permissioned/consortium blockchains and provides immediate, deterministic finality, meaning once a block is validated, it cannot be forked or reversed. This is critical for high-value financial settlements where certainty is required within seconds. PoW and PoS variants have probabilistic finality and can experience temporary forks, which is unacceptable for this use case.

The pattern of storing cryptographic hashes (digital fingerprints) of documents on-chain, while keeping the sensitive documents themselves in a traditional off-chain system, provides a perfect balance. The immutable blockchain proves the existence and integrity of the private documents (like invoices with prices) at a specific time, without revealing their confidential contents to unauthorized parties on the network.

This describes a classic Reentrancy attack. The attacker’s malicious contract calls the vulnerable payment function and, before the victim contract’s balance is updated, the attacker’s fallback/receive function is triggered, which calls the payment function again. This recursive loop allows multiple withdrawals for the price of one, draining funds. It was famously exploited in The DAO hack.

The Ethereum mainnet alone struggles with high fees and lower throughput for micro-transactions. A Layer-2 scaling solution (like Polygon, Arbitrum, Optimism) or a sidechain provides the high throughput and low fees required, while maintaining compatibility with Ethereum’s tooling and the widely-used Solidity/JavaScript ecosystem. This allows the JavaScript-proficient team to build effectively.

A nonce (number used once) has two key uses. In Proof of Work mining, miners change the nonce in a block header to find a hash that meets the network’s difficulty target. In user transactions, a nonce is a sequential count that prevents replay attacks; a transaction with a specific nonce can only be executed once on the network.

True deletion from an immutable ledger is contradictory. The practical solution is to use the blockchain for its strengths—providing an immutable audit log of data access and provenance—while storing the sensitive, regulated data itself in a traditional, compliant database. The on-chain hash proves the off-chain data’s integrity at any point in time, and the off-chain system can perform legally-mandated deletions.

Blockchain introduces complexity and overhead (consensus, replication, etc.). If a single entity controls all aspects of the data and process, a traditional, optimized centralized database is almost always faster, cheaper, and more efficient. Blockchain’s value emerges in multi-party, trust-minimized environments where no single party should have unilateral control.

A multisignature wallet is a specific type of wallet that requires M-of-N signatures to authorize a transaction. A smart contract wallet is a broader category: it is a wallet whose logic is governed by a smart contract. This contract can implement multisig, but also other rules like daily spending limits, time locks, recovery schemes, or integration with other dApps. It offers far more programmability.

Hyperledger Fabric separates transaction execution (done by peers) from transaction ordering. The Ordering Service (or Orderer) is a modular component responsible for receiving endorsed transactions, agreeing on their total order, and packaging them into blocks. It does not execute transactions or maintain the ledger. This separation allows for scalability and flexibility in consensus mechanisms (like Raft).

Practical Byzantine Fault Tolerance (PBFT) is designed for permissioned/consortium blockchains and provides immediate, deterministic finality, meaning once a block is validated, it cannot be forked or reversed. This is critical for high-value financial settlements where certainty is required within seconds. PoW and PoS variants have probabilistic finality and can experience temporary forks, which is unacceptable for this use case.0