✅Quiz

Secureum Bootcamp Ethereum 101 Quiz • Ventral DigitalVentral Digital

Q1 Ethereum Virtual Machine is a

• A) Register-based virtual machine

• B) Stack-based virtual machine

• C) Heap-based virtual machine

• D) Stackless virtual machine

Q2 The length of addresses on Ethereum is

• A) 256 bits

• B) 20 bytes

• C) Depends on Externally-Owned-Account or Contract address

• D) Configurable

Q3 The types of accounts on Ethereum are

• A) All Accounts are the same

• B) Permissioned Accounts and Permissionless Accounts

• C) Externally-Owned-Accounts and Contract Accounts

• D) User Accounts and Admin Accounts

Q4 The difference(s) between Bitcoin and Ethereum is/are

• A) The underlying tokens: Bitcoin vs Ether

• B) Smart contract support

• C) UTXO vs Accounts

• D) Nakamoto Consensus

Q5 Ethereum smart contracts do not run into halting problem because

• A) EVM is not Turing Complete

• B) EVM is Turing Complete

• C) EVM is Turing Complete but is bounded by gas sent in transaction

• D) EVM is Turing Complete but is bounded by the stack depth

Q6 Ethereum nodes talk to each other via

• A) Peer-to-Peer network

• B) Client-Server network

• C) Satellite network

• D) None of the above

Q7 A nonce is present in

• A) Ethereum transaction

• B) Ethereum account

• C) Both A & B

• D) Neither A nor B

Q8 The gas tracking website https://etherscan.io/gastracker says that Low gas cost is 40 wei This affects

• A) The transaction gasPrice

• B) The transaction gasLimit

• C) The transaction value

• D) Both B & C

Q9 The number of transactions in a Ethereum block depend on

• A) Nothing. It is a constant.

• B) Gas used by transactions

• C) Block gas limit

• D) Block difficulty

Q10 Miners are responsible for setting

• A) Transaction gas price

• B) Block gas limit

• C) Both A & B

• D) Neither A nor B

Q11 User A sends transaction T1 from address A1 with gasPrice G1 and later transaction T2 from address A2 with gasPrice G2

• A) T1 will be always included in an earlier block than T2

• B) Inclusion/Ordering of these transactions depends only on gas prices G1 and G2

• C) Inclusion/Ordering of these transactions depends only on network congestion

• D) Inclusion/Ordering of these transactions depends on miners

Q12 Which of the following statements is/are true about gas?

• A) Unused gas is returned to the transaction destination account -> returned to the sender's address

• B) Gas used by the transaction is credited to the beneficiary address in block header

• C) Unused gas is credited to the beneficiary address in block header

• D) Both A & B

Q13 Which of the following EVM components is/are non-volatile across transactions?

• A) Stack

• B) Memory

• C) Storage

• D) Calldata

Q14 Which of the following operation(s) touch(es) storage?

• A) SWAP -> stack

• B) SLOAD

• C) DUP -> stack

• D) PUSH -> stack

Q15 Which of the following statement(s) is/are false?

• A) EVM can get the block number only of the current block

• B) EVM can get the block hash only of the current block

• C) EVM can get the account balance only of the current account

• D) EVM can get the code hash only of the current account

Comment:

0x31 BALANCE 1 1 Get balance of the given account 0x3f EXTCODEHASH 1 1 Get hash of an account’s code 0x40 BLOCKHASH 1 1 Get the hash of one of the 256 most recent complete blocks 0x43 NUMBER 0 1 Get the block’s number

from points 70, 71 of Ethereum 101 - by Secureum

Q16 Which of the following information cannot be obtained in the EVM?

• A) Block difficulty

• B) Transaction logs

• C) Balance of an account

• D) Block hash of any block

Comment:

0x31 BALANCE 1 1 Get balance of the given account 0x40 BLOCKHASH 1 1 Get the hash of one of the 256 most recent complete blocks 0x44 DIFFICULTY 0 1 Get the block’s difficulty

(there's no operation to access transaction logs)

from points 70, 71 of Ethereum 101 - by Secureum

Q17 Which call instruction could be used to allow modifying the caller account’s state?

• A) CALL

• B) CALLCODE

• C) DELEGATECALL

• D) STATICALL

Comment:

0xf1 CALL 7 1 Message-call into an account 0xf2 CALLCODE 7 1 Message-call into this account with an alternative account’s code 0xf4 DELEGATECALL 6 1 Message-call into this account with an alternative account’s code, but persisting the current values for sender and value 0xfa STATICCALL 6 1 Static message-call into an account

from point 77 of Ethereum 101 - by Secureum

Another variant of call is delegatecall, which replaced the more dangerous callcode. [...] Essentially, delegatecall runs the code of another contract inside the context of the execution of the current contract.

from "Calling Other Contracts (send, call, callcode, delegatecall)" of Mastering Ethereum

Permits non-state-changing calls to itself or other contracts while disallowing any modifications to state during the call (and its subcalls, if present) to increase smart contract security and assure developers that re-entrancy bugs cannot arise from the call.

from "Appendix A: Ethereum Standards" of Mastering Ethereum

Q18 The most gas-expensive operation is

• A) SLOAD

• B) SSTORE

• C) CREATE

• D) SELFDESTRUCT

Q19 Transaction T1 attempts to write to storage values S1 and S2 of contract C. Transaction T2 attempts to read the same storage values S1 and S2. However, T1 reverts due an exception after writing S1 but before writing S2. Which of the following is/are true?

• A) T2 reads the value of S1 updated by T1

• B) T2 reads the value of S1 prior to T1’s attempted update

• C) T2 also reverts because of the dependency on T1

• D) This scenario is not possible

Q20 Ethereum’s threat model is characterised by

• A) Trusted miners and users

• B) Trusted users, untrusted miners

• C) Trusted miners, untrusted users

• D) Everyone is untrusted

Q21 The number of modified Merkle-Patricia trees in an Ethereum block is

• A) One

• B) Three

• C) Three plus number of contract accounts -> stateRoot, transactionsRoot and receiptsRoot, plus one for each contract account

• D) Three plus number of transactions included in the block

Comment:

Blocks contain block header, transactions and ommers’ block headers. Block header contains [...] `stateRoot`, `transactionsRoot` and `receiptsRoot` are 256-bit hashes of the root nodes of modified Merkle-Patricia trees.

from points 53, 54 of Ethereum 101 - by Secureum

Q22 EVM is not a von Neumann architecture because

• A) It was co-founded by Vitalik Buterin, not John von Neumann

• B) Program instructions are stored separately from data

• C) Program instructions are stored in a ROM not RAM

• D) It is quasi Turing complete

Q23 EVM stores

• A) Most significant byte in the smallest memory address

• B) Most significant byte in the largest memory address

• C) In Big-endian order

• D) In Little-endian order

Q24 Miners are incentivized to validate and create new blocks by

• A) Block rewards

• B) Altruism

• C) Transaction fees

• D) Their belief in decentralization

Q25 Hardfork on Ethereum

• A) Has never happened

• B) Happened only once after the DAO attack

• C) Happens with backwards-incompatible protocol changes

• D) Happens when developers and miners disagree on changes

Q26 Gas for EVM opcodes

• A) Is constant and the same for all opcodes

• B) May be changed over time to prevent DoS attacks

• C) Depend on the gas price

• D) Depend on the miners

Q27 Smart contracts on Ethereum

• A) May be deployed by anyone

• B) May be deployed only through the DApp store

• C) May have some form of access control

• D) Are guaranteed to be secure

Q28 EVM opcodes

• A) Are multi-byte instructions

• B) Are single byte instructions

• C) Take operands in registers

• D) Take operands on stack

Q29 Security of Ethereum DApps depend on

• A) Security of their smart contracts

• B) Security of their off-chain components

• C) Security of Ethereum

• D) None of the above

Q30 Security Audits for smart contracts are performed because

• A) They are required for listing DApp on the DApp store

• B) They are required for deployment on Ethereum

• C) They help remove vulnerabilities and reduce risk

• D) They are required by exchanges to list tokens

Q31 The high-level languages typically used for writing Ethereum smart contracts are

• A) Go

• B) C++

• C) Vyper

• D) Solidity

Q32 The number of decimals in Ether is

• A) 0

• B) 1

• C) 18

• D) Configurable