Ethereum

Question 1

What are Proof-of-work and proof-of-stake

Answer 1

• Not consensus protocols
• They are actually Sybil resistance mechanisms and block author selectors; they are a way to decide who is the author of the latest block.

Question 2

What is Sybil resistance and sybil attack

Answer 2

Sybil attacks are when one user or group pretends to be many users.

Question 3

How does PoW work

Answer 3

Miners must find combination and order of transactions, and find some value nonce, that combined calculates hash that satisfy an arbitrary, difficult condition.
Condition example: block must start with 6 zeros.

Question 4

What is the name of ethereum consensus mechanism

Answer 4

Gasper

Question 5

What is attestation

PoS

Answer 5

The validator then sends a vote (called an attestation) in favor of that block across the network.

Question 6

How does PoS work

Answer 6

• In every slot a validator is randomly selected to be the block proposer. They bundle transactions together, execute them and determine a new ‘state’ and send new block.
• In every slot, a committee of validators is randomly chosen, whose votes are used to determine the validity of the block being proposed.

Question 7

What is PoS chain selection rule

Answer 7

The algorithm that measures the ‘weight’ of the chain.
The weight is the accumulated sum of validator votes, weighted by validator staked-ether balances.

Question 8

Transaction Finality in PoS

Answer 8

• On proof-of-stake Ethereum, this is managed using “checkpoint” blocks
• Validators vote for pairs of checkpoint epochs that it considers to be valid.
• If a pair of checkpoints attracts votes representing at least two-thirds of the total staked ETH, the checkpoints are upgraded.
• The more recent of the two (target) becomes “justified”. The earlier of the two is already justified because it was the “target” in the previous epoch. Now it is upgraded to “finalized”.

Question 9

What is the inactivity leak

PoS

Answer 9

The inactivity leak bleeds away the staked ETH from validators voting against the majority, allowing the majority to regain a two-thirds majority and finalize the chain.

Question 10

What is correlation penalty

PoS

Answer 10

The amount of ETH slashed depends on how many validators are also being slashed at around the same time. This is known as the “correlation penalty”.

Question 11

What is temporary fork

Answer 11

When two blocks are created at the same time by two different nodes, the respective peers of those diverging nodes will be operating on two different versions of the blockchain.

Question 12

What is Hard Fork

Answer 12

When community disagrees on blockchain rule, part can use old chain, and part can use new chain (i.e. with new consensus or some security patch).

Question 13

How much ether is creating with each block (in PoS)

Answer 13

• The total amount issued depends on the number of validators and how much ether they have staked.
  About 1/8 of the total issuance goes to the block proposer; the remainder is distributed across the other validators.

Question 14

How much is Wei in ether

Answer 14

10^-18

Question 15

How much is Gwei in ether

Answer 15

10^-9

Question 16

What are bootnodes

Answer 16

• These are well-known, relatively reliable IP addresses that can be used to create a sufficiently large pool of network peer connections.
• Every major Ethereum node software has a hardcoded list of bootnodes.

Question 17

How is time divided in ethereum (what is block time).
Name of interval and how many seconds.

PoS

Answer 17

In Ethereum, time is divided up into twelve second units called ‘slots’.
Assuming all validators are online and fully functional there will be a block in every slot, meaning the block time is 12s.
1 Epoch = 32 Slots

Question 18

How does account / transaction nonce work

Answer 18

A crytopgraphic nonce is a technique to prevent replay attacks, and matches the purpose of the account nonce.

Question 19

How is public address created

Answer 19

It’s derived from the public key.
You get a public address for your account by taking the last 20 bytes of the Keccak-256 hash of the public key and adding 0x to the beginning.

Question 20

EVM

Answer 20

The Ethereum Virtual Machine is the global virtual computer whose state every participant on the Ethereum network stores and agrees on. Any participant can request the execution of arbitrary code on the EVM; code execution changes the state of the EVM.
Compiled smart contract bytecode executes as a number of EVM opcodes.

Question 21

How is ethereum state stored

Answer 21

In the context of Ethereum, the state is an enormous data structure called a modified Merkle Patricia Trie, which keeps all accounts linked by hashes and reducible to a single root hash stored on the blockchain.

Question 21

What is Gas

Answer 21

• Gas points are used to specify the fees inside of Ether, for ease of computation using standard values.
• Ethereum has specified gas points for each type of operation.
• If the fee specified and the gas point in the transaction are not sufficient, it is rejected. This is similar to mailing a letter with insufficient postage.

Question 22

In what unit gas is denoted

Answer 22

Gas prices are denoted in gwei.

Question 23

Why do gas fees exist?

Answer 23

• By requiring a fee for every computation executed on the network, we prevent bad actors from spamming the network.

Question 24

What is Layer 2

Answer 24

* A layer 2 is a separate blockchain that extends Ethereum and inherits the security guarantees of Ethereum. * A layer 2 blockchain regularly communicates with Ethereum (by submitting bundles of transactions) in order to ensure it has similar security and decentralization guarantees.

Question 25

What is EOA

Answer 25

Externally Owned Accounts (EOA) - Needed to participate in network. - Controlled by private keys. - Every account has a coin balance. - Creating an account costs nothing

Question 26

What is Contract Accounts

Answer 26

- Has code which can be executed (smart contract) - Can modify own state and interact with deployed smart contracts as well. - Creating a contract has a cost because you're using network storage.

Question 27

Base Fee

Answer 27

* The base fee is calculated independently of the current block and is instead determined by the blocks before it - making transaction fees more predictable for users. When the block is mined this base fee is "burned", removing it from circulation. * The base fee is calculated by a formula that compares the size of the previous block (the amount of gas used for all the transactions) with the target size. * This exponential growth makes it economically non-viable for block size to remain high indefinitely.

Question 28

Why base fee is burned | London hard fork

Answer 28

Burning the base fee prevents various ways block producers could manipulate it otherwise. For example, if block producers received the base fee, they could include their own transactions for free and raise the base fee for everyone else.

Question 29

What is block size | London hard fork

Answer 29

* Previously, the block size was constant. * The London Upgrade introduced variable-size blocks to Ethereum. Each block has a target size of 15 million gas, but the size of blocks will increase or decrease in accordance with network demand, up until the block limit of 30 million gas (2x the target block size)

Question 30

Beacon Chain Contract

Answer 30

All PoS stakes are stored in beakon chain contract.

Question 31

Block: gas_limit

Answer 31

maximum gas allowed in this block

Question 32

Block: gas_used

Answer 32

the actual amount of gas used in this block

Question 33

Block: state_root

Answer 33

root hash for the global state after applying changes in this block

Question 34

Block: graffiti

Answer 34

arbitrary data used to tag blocks

Question 35

Block: randao

Answer 35

a value used to select the next block proposer

Question 36

Block: attestations

Answer 36

list of attestations in favor of the current block

Question 37

Why would you send ether in tx to execute contract method

Answer 37

When the recipient address is a smart contract, this transferred ether may be used to pay for gas when the smart contract executes its code.

Question 38

Transaction: gasLimit

Answer 38

the maximum amount of gas units that can be consumed by the transaction.

Question 39

Transaction: maxPriorityFeePerGas

Answer 39

the maximum price of gas to be included as a tip to the validator

Question 40

Transaction: maxFeePerGas

Answer 40

the maximum price of gas willing to be paid for the transaction (inclusive of baseFeePerGas and maxPriorityFeePerGas)

Question 41

What is the name of the place where transaction end up just after send

Answer 41

unverified transactions pool (Mempool)

Question 42

What is transaction Receipt, what are important fields

Answer 42

- Transaction Receipts record the transaction outcome. - Important fields: - status: String - '0x0' indicates transaction failure , '0x1' indicates transaction succeeded. - contractAddress: String - 20 Bytes - The contract address created, if the transaction was a contract creation, otherwise null. - logs: Array - Array of log objects, which this transaction generated.

Question 43

Types of transactions

Answer 43

- Regular transactions: a transaction from one account to another. - Contract deployment transactions: a transaction without a 'to' address, where the data field is used for the contract code. - Execution of a contract: a transaction that interacts with a deployed smart contract. In this case, 'to' address is the smart contract address.

Question 44

What is dApp

Answer 44

A decentralized application (dapp) is an application built on a decentralized network that combines a smart contract and a frontend user interface.

Question 45

Ethereum node types

Answer 45

- Full node - Light node - Archive node

Question 46

What is Byzantine fault, what is BFT

Answer 46

- A condition in distributed systems where components may fail or misbehave, and it's unclear if they have failed. - Named after the **Byzantine Generals Problem** — where reaching consensus is hard when communication is unreliable or participants are untrustworthy. **The Byzantine fault tolerance (BFT)** The Byzantine fault tolerance (BFT) system is a set of algorithms and protocols that allows a distributed system to function correctly even when some of the components malfunction or act maliciously

Question 47

Two types of Ethereum (and Bitcoin) wallets

Answer 47

- The first type is a **nondeterministic wallet**, where each key is independently generated from a different random number. The keys are not related to each other. This type of wallet is also known as a **JBOK wallet**, from the phrase "Just a Bunch of Keys.” - The second type of wallet is a **deterministic wallet**, where all the keys are derived from a single master key, known as the **seed**. All the keys in this type of wallet are related to each other and can be generated again if one has the original seed.

Question 48

What is HD Wallet

Answer 48

Deterministic wallets were developed to make it easy to derive many keys from a single seed. Currently, the most advanced form of deterministic wallet is the **hierarchical deterministic (HD) wallet** defined by Bitcoin’s BIP-32 standard.