Blockchain Technology Cheat Sheet 2026

The 30 highest-yield Blockchain Technology facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. Why are private keys never transmitted during a transaction? → Signatures prove ownership without revealing the key
2. In Proof of Work, what does the 'difficulty' parameter primarily control? → The expected time to find a valid block
3. Which consensus algorithm is specifically designed to tolerate up to one-third of nodes acting maliciously? → Practical Byzantine Fault Tolerance (PBFT)
4. What is the benefit of encrypting peer-to-peer connections between nodes? → Prevents eavesdropping and traffic tampering
5. How are transactions ordered within a block's Merkle tree construction? → In a defined, deterministic order so the root is reproducible
6. In ERC-20, what is the well-known race-condition risk associated with the approve() function? → A spender can front-run a changed approval and spend both the old and new amounts
7. Why is Blockchain a trusted approach? → All of the above
8. Which attack involves sending tiny amounts of cryptocurrency to many addresses to break the privacy of wallet owners through later transaction analysis? → Dusting attack
9. What is a key defense against DDoS attacks targeting public-facing nodes? → Use of upstream DDoS mitigation and traffic scrubbing
10. Describe cold storage. → A private key that isn't linked to the internet
11. Why are time-weighted average price (TWAP) oracles more resistant to flash loan attacks? → They average prices over time, resisting single-block manipulation
12. A proxy upgrade pattern introduces which key security concern? → A compromised admin can swap in malicious implementation logic
13. Which design principle helps prevent reentrancy vulnerabilities? → Checks-Effects-Interactions pattern
14. What does 'stake grinding' attempt to exploit? → Manipulating the randomness used to select the next block proposer
15. What is 'chain reorganization' (reorg) in a blockchain? → Replacing blocks with a different competing branch
16. How does each block in a blockchain link to the previous one? → By storing the previous block's hash in its header
17. Which of the following biockchains has an architectural design that is channel-focused? → Hyperledger
18. What does deterministic execution guarantee in smart contract architecture? → Every node computes the same result
19. On a public Blockchain, who can read the records? → Everyone on the Blockchain
20. What is the primary purpose of a 'finality gadget' like Casper FFG? → To provide checkpoints that make blocks irreversible
21. What does 'liveness' guarantee in a consensus protocol? → The system continues to make progress and process new transactions
22. What is a 'flash loan' in DeFi? → An uncollateralized loan that must be borrowed and repaid within the same transaction
23. Why do most dApps store large files on IPFS or Arweave rather than directly on-chain? → On-chain storage is extremely expensive per byte and bloats the chain
24. What is one typical way for "chaining" pieces of data together in sequence in a blockchain design? → Store the hash of the previous block within the current block
25. Which event must an ERC-20 token emit when tokens move between addresses? → Transfer(from, to, value)
26. What hook does ERC-777 introduce that can create a reentrancy risk if not handled carefully? → tokensReceived, called on the recipient during a transfer
27. In ZK-Rollup terminology, what does the 'sequencer' do? → Orders, batches, and submits transactions to Layer 1 on behalf of users
28. In a Merkle tree, what is stored at each leaf node? → The hash of an individual transaction
29. What is the danger of an unprotected 'delegatecall' to an attacker-controlled address? → The attacker's code runs in the caller's storage context and can overwrite state
30. A read-only reentrancy attack abuses what specifically? → A view function returning inconsistent state mid-execution