Advanced Blockchain: Scalability, Security, and BaaS
Free EC-Council Certified Blockchain Professional practice — 6 questions on Advanced Blockchain: Scalability, Security, and BaaS, with explanations. No sign-up. Full 12-question mixed test →
A DeFi lending contract's withdraw() function first calls the user's external address to transfer ETH, and only after that call returns does it decrement the user's internal balance mapping. An attacker's malicious contract, invoked via the transfer, calls withdraw() again before the balance is decremented, repeatedly draining funds. What is the ROOT CAUSE of this vulnerability?
Classic reentrancy (the DAO hack pattern): state (the balance) must be updated BEFORE any external call is made, per the checks-effects-interactions pattern, so a re-entrant call sees the already-decremented balance and cannot repeat the withdrawal.
A blockchain gaming platform needs thousands of instant, near-zero-fee transactions per second exchanged strictly between two known parties (a player and the game server), with only the final net balance ever committed on the main chain when the session closes. Which scaling solution is the BEST fit?
State channels are purpose-built for high-frequency, low-latency interaction between a small, FIXED set of known participants: parties exchange signed state updates off-chain and only submit the final state on-chain, with no per-transaction gas cost and instant finality between the two parties.
To defend a Solidity function against reentrancy attacks, a common mitigation pattern uses a boolean 'lock' variable set to true at function entry and false at exit, reverting any nested call attempt while the lock is active. What is this pattern/modifier commonly called?
The 'nonReentrant' mutex (popularized by OpenZeppelin's ReentrancyGuard) uses exactly this lock-flag mechanism to prevent a function from being re-entered while it is still executing, directly blocking recursive reentrancy attacks.
An exchange holds a large amount of customer crypto assets in cold storage and wants to eliminate any single point of failure so that no single compromised employee or device can move the funds. Which key management approach BEST satisfies this requirement?
An M-of-N multisignature scheme distributes signing authority across multiple independent key holders in separate locations, so compromising or coercing any single individual (or device) is insufficient to move funds — directly eliminating the single point of failure.
A startup wants to prototype a consortium blockchain for supply-chain tracking without procuring servers or managing node patching/upgrades, while still retaining full control over its custom smart contract logic. Which approach BEST meets this requirement?
BaaS platforms handle node provisioning, patching, monitoring, and consensus configuration as a managed service, while still allowing the customer to deploy and customize their own smart contracts and business logic on top — exactly matching the stated needs.
Researchers commonly describe blockchain design as facing a fundamental trade-off: a system can strongly optimize for at most two of three properties — decentralization, security, and scalability — without sacrificing the third. What is this open research problem called?
The Scalability Trilemma (popularized by Vitalik Buterin) is the recognized open research challenge stating that blockchain systems struggle to simultaneously maximize decentralization, security, and scalability — much scaling research (sharding, rollups, sidechains) exists specifically to try to work around this trade-off.
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