CSE598 Blockchain Final

Where are the transactions recorded in a blockchain?

* On a SQL database

* On a distributed immutable ledger

* On a distributed opaque immutable ledger

* On a centralized immutable ledger

On a distributed immutable ledger

If the following are the six steps in the process of creating a new block, what is the right time sequence in which the process happens?

1. Nodes verify transactions

2. Transactions were submitted to the network

3. Consensus algorithm

4. Select the header of the most recent block and insert it into the new block as hash

5. Bundle the transactions into a block

6. New block is added to the local blockchain and propagated to the network

2,1,5,4,3,6

2. Transactions were submitted to the network

1. Nodes verify transactions

5. Bundle the transactions into a block

4. Select the header of the most recent block and insert it into the new block as hash

3. Consensus algorithm

6. New block is added to the local blockchain and propagated to the network

Which of the following is used to point to a block in the blockchain:

* Hash pointer

* User ID

* Transaction ID

* Timestamp

Hash pointer

TF: A block in the blockchain can have more than one parent block.

False

In Ethereum it is stated that the ledge of a cryptocurrency such as Bitcoin can be thought of as what?

* A smart contract

* A state machine replication

* A state transition system

* A decentralized autonomous organization

State transition system

A blockchain configuration that allows participating members to come from within its organization defines

private or permissioned

Which of these are NOT contained in a block of a blockchain?

* The hash value of the last block in the chain

* The has value of the block

* The has value of the previous block in the chain

* Data that is stored in the block

The has value of the last block in the chain

Any electronic device that maintains a copy of the blockchain and keeps the network functioning is called a

* Server

* Node

* Token

* Reward

Node

Blockchain is "immutable". What does it imply?

* The cannot be altered

* They can only store numerical data

* Any user cannot access them

* Their computation speed is not limited

They cannot be altered

If a hacker wanted to alter a blockchain, what percentage of the block copies would he have to alter?

51%

Suppose you have eight data points - 1 to 8. The post-order traversal of the Merkle Tree is given by (here 8 means hash of 8, 43 means to combined hash of 4 and 3, and so on)

* {8, 7, 87, 6, 5, 65, 8764, 4, 3, 43, 2, 1, 21, 4321, 87654321}

* {8, 87, 7, 8764, 6, 65, 5, 87654321, 4, 43, 3, 4321, 2, 21, 1}

* {1, 2, 12, 3, 4, 34, 1234, 5, 6, 56, 7, 8, 78, 5678, 12345678}

* {87654321, 8765, 87, 8, 7, 65, 6, 5, 4321, 43, 4, 3, 21, 2, 1}

{1, 2, 12, 3, 4, 34, 1234, 5, 6, 56, 7, 8, 78, 5678, 12345678}

What is one of the requirements of secure hashing function?

* It is an ECC function

* It is a one-way function

* It is a log function

* It is a secret function

It is a one-way function

Given an input m1 it should be difficult to find another input m2 such that m1 != m2 and hash(m1)=hash(m2). This property is called?

* Second preimage resistance

* Collision resistance

* Replay attack resistance

Second Preimage Resistance

What will be the height of the hash tree with branching factor 2 and with 8 records?

4

The Merkle Trees are constructed in a?

* Bottom-up approach

* Top-down approach

* Both

Bottom-up approach

A hash function takes an input string with

* Alphabets

* Multimedia

* Numbers

* All of the above

Alphabets, multimedia, numbers

What is the variable that the nodes mining bitcoin race to solve?

* Target value

* Nonce

* Hash power

* Transaction volume

Nonce

What is the value of 2 times 2 if we are working in the field of six elements(0, 1, 2, 3, 4, 5, 6)?

4

Perform the following operation in a finite field with 11 elements. Express all answers as a number 0 through 10. Operation 7*8

1

If we have 0.005 (0.5%) chance of finding a Dash block in 150 seconds, what is the chance that we don't find a block the next day? The total number of 150-second periods in a day is 576.

0.0557

Experience has shown that 1/200 of all CDs produced by a certain machine are defective. If a quality control technician randomly tests twenty CDs, compute each of the following probabilities:

a) P(exactly one is defective)

b) P(half are defective)

c) P(no more than two are defective)

0.09

0.00

1.00

Researchers find that the chance of any baby rabbit born to a rabbit carrying a gene for illness X is 1 out of 4. If the rabbit has three babies, what is the likelihood that exactly two of them will carry the gene for illness X?

0.14

Bob is receiving a message from Alice. She is anxious to prevent any message tampering while it is being sent. What cryptographic objective is Alice aiming to accomplish?

* Confidentiality

* Nonrepudiation

* Integrity

* Authentication

Integrity

What is public in a public key cryptosystem?

* Encryption key

* Decryption key

* Both

Encryption key

TF: Alice and Bob played a game: each must secretly turn a coin into heads or tails and then reveal their coin. If the coins are matching heads or tails, then player A keeps both coins. If the coins don't match, player B keeps both coins. This follows Nash equilibrium.

False

What data field in a transaction's output is used to refer to it in a subsequent transaction?

* "address"; This data field allows a future transaction to reference the specific address intended for the output.

* "n"; This data field allows a future transaction to reference the specific output in a transaction that is to be spent.

* "txid"; This data field allows a future transaction to reference the specific transaction this output is located in.

* "scriptPubKey"; This data field allows a future transaction to reference the specific locking script used in the output.

'n': this data field allows a future transaction to reference the specific output in a transaction that is to be spent

Given this input script: 3 5

And this output script: A B 3 OP_EQUAL

What two opcodes should replace A and B to make this a valid transaction?

* A: OP_DUP, B: OP_EQUAL

* A: OP_DUP, B: OP_EQUALVERIFY

* A: OP_EQUAL, B: OP_DUP

* A: OP_EQUALVERIFY, B: OP_DUP

A: OP_DUP, B: OP_EQUALVERIFY

Given this output script:

OP_IF

OP_CHECKSIG

OP_ELSE

OP_CHECKSIG

Which of the following input scripts will results in the valid transaction?

* 0

* 1

* 0

* 1

1

What is the initial limitation placed on a state channel before any transaction is broadcasted to the network?

* A state channel is limited by the number of transactions allowed defined in the initial multi-signature transaction

* A state channel is limited by the number of transactions allowed defined in the refund transaction

* A state channel is limited by the time lock defined in the refund transaction

* A state channel is limited by the time lock defined in the initial multi-signature transaction

A state channel is limited by the time lock defined in the refund transaction

What is the desired outcome when using mnemonic codes?

* To easily convert a human-made sentence into an initial generation seed for a wallet

*To easily encode the initial generation seed of a wallet in the human-readable format

* To easily create child keys from other child keys in a hierarchical deterministic wallet

* To easily convert a private key into a public key for user in a wallet

To easily encode the initial generation seed of a wallet in the human-readable format

Which wallet type would use this key generation algorithm?

The nth private key = SHA256(seed + n)

* Deterministic wallet

* Non-deterministic wallet

* Hierarchical deterministic wallet

Deterministic wallet

If all standard P2PKH locking scripts were replaced by standard P2SH locking scripts for all unspent transaction outputs, what would happen to the size of the UTXO set?

* The size of the UTXO set would decrease because P2SH locking scripts are smaller in size than P2PKH locking scripts

* The size of the UTXO set would not change because P2SH locking scripts are the same size as P2PKH locking scripts

* The size of the UTXO set would increase because P2SH locking scripts are larger in size that P2PKH locking scripts

* The size of the UTXO set would not change because the size of the UTXO set is independent of the size of the locking scripts

The size of the UTXO set would decrease because P2SH locking scripts are smaller in size than P2PKH locking scripts

In the time-based bidirectional state channel example, what did each succeeding intermediary transaction's nLockTime field do?

Increase

No change

Decrease

Decrease

A miner need to hash the __________ and obtain a value under the target in order to mine a valid block.

* Nonce

* Transactions

* Block

* Block header

Block header

A fee for a transaction is determined by

* Subtracting the total outputs from the total inputs

* A field in the transaction that enumerates what the fee is

* Many nodes vote until they come to consensus

* The hash of the transaction

Subtracting the total outputs from the total inputs

Calculations we have done provide that it could take years before a small miner might expect to see a block. For this reason, miners may join a mining pool in order to

* Have a more manageable and continuous revenue stream

* Secure the network

Have a more manageable and continuous revenue stream

TF: In bitcoin, the set of all outputs of transactions that are spent is abbreviated to the UTXO set

False

A social attack can be performed on

* Users and/or devs

* Users and handware

* Hardware and/or cryptography

Users and/or devs

TF: Miners can join and leave the network at any time

True

What is a bitcoin halving?

* An event that reduces bitcoin price

* An event that reduces rewards for mining bitcoin

* An event that divides bitcoin into the two different coins

An event that reduces rewards for mining bitcoin

On average how often is a new block of bitcoin mined?

* 24 hours

* 1 hour

* 10 minutes

* 1 month

10 minutes

In PBFT algorithms, what is the minimum required number of total nodes to provide safety and liveness for up to f faulty nodes?

* 2f

* 2f + 1

* 3f

* 3f + 1

3f + 1

In a PBFT-based blockchain if there are 100 faulty nodes, how many total nodes are required by the network such that the network still provides safety and liveness?

* 250

*301

* 101

* 200

301

A blockchain consensus algorithm where finality can be delayed due to forks needing to be resolved favors which consensus property, safety, or liveness?

* This consensus algorithm favors liveness over safety

* This consensus algorithm favors safety over liveness.

* This consensus algorithm does not favor either consensus property.

This consensus algorithm favors liveness over safety

What general engineering situations does the Byzantine Generals Problem apply to?

* BGP applies to any distributed computer system solutions needing to function reliably while a certain number of system components are allowed to malfunction and/or information exchanged between system components may get temporarily disrupted or partially corrupted.

* BGP applies to any distributed computer system solutions needing to function reliably while any number of system components might malfunction.

* BGP applies to any computer system solutions needing to function reliably in situations where information exchange between system components gets temporarily disrupted or partially corrupted.

BGP applies to any distributed computer system solutions needing to function reliably while a certain number of system components are allowed to malfunction and/or information exchanged between system components may get temporarily disrupted or partially corrupted.

In Delegated Proof-of-Stake, what action do stakeholders perform?

* Stakeholders are block proposers

* Stakeholders are block producers

* Stakeholders elect block proposers

* Stakeholders elect block producers

Stakeholders elect block producers

A side effect as transactions as Proof of Stake acts as security against what type of attack?

* DoS attack

* Sybil attack

* Long-range attacks

* Stake-grinding attacks

Long-range attacks

What is required for decentralized blockchains to pick a block producer?

* Source of randomness or pseudo-randomness

* Race using some type of computational puzzle

* Quorum of potential block producers determined

* Deposit of the underlying asset by the block producer

Source of randomness or pseudo-randomness

TF: A consensus algorithm is a procedure through which all the peers of the Blockchain network reach a common agreement about the present state of the distributed ledger.

True

TF: A consensus algorithm allows the blockchain to validate and confirm transactions and operations, without the need for a third-party intermediary.

True

TF: Proof of Work is more energy efficient compared to Proof of Stake

False

Which node can independently verify every transaction on the blockchain?

* Routing

* Full

* Wallet

* Mining

Full

What is the necessary process for a brand new node to connect to the Bitcoin network if there are no DNS seeds provided?

* A brand new node can connect to the Bitcoin network by finding the IP address of a connected node and attempting to communicate.

* DNS seeds must be provided for a new node to connect to the Bitcoin network.

* A brand new node can connect to the Bitcoin network by broadcasting its IP address and that they are a new node attempting to connect.

A brand new node can connect to the Bitcoin network by finding the IP address of a connected node and attempting to communicate.

In traditional block propagation, what is transmitted in response to a getdata message?

* Block header

* Full block

* Hash of a block

* Hash of a block header

Full block

Why is it recommended that a node to be connected to multiple nodes?

* It is recommended because connections between nodes can be dropped at any time

* It is recommended because connection to multiple nodes increases data transfer speed.

* It is recommended because it helps to accelerate propagation of transactions across the network.

* It is recommended because it helps to accelerate propagation of transactions across the network.

It is recommended because connections between nodes can be dropped at any time

How do SPV clients combat the privacy risk associated with requesting specific information from the blockchain?

* SPV clients give a bloom filter to their connected full node that correctly maps the data they are interested in.

* SPV clients specify more addresses than what they are actually interested in.

* SPV clients are required to connect to multiple random full nodes such that no single full node knows if they are sending the actual information of interest.

* SPV clients only give a portion of the address they are interested in such that the full node sends all information of any address that includes that portion.

SPV clients give a bloom filter to their connected full node that correctly maps the data they are interested in.

Compact blocks are based on what idea?

* That by reducing the size of the block via encryption, transmitting the encrypted block, and decrypting the block after transmission, overall network bandwidth usage decreases.

* That nodes have similar transactions and only the difference in local data needs to be completely transmitted.

* That the full complete data within a block can be represented in a more compact form during transmission.

* That by requesting full blocks in compact chunks from multiple peers, overall network bandwidth usage decreases.

That nodes have similar transactions and only the difference in local data needs to be completely transmitted.

During full node bootstrapping, what message is sent, containing the block hash of their latest local block, to compare local blockchains between nodes?

* getblocks message

* getdata message

* inv message

* block message

getblocks message

TF: A decentralized file-sharing protocol that allows nodes within the network to both upload and downloads files from each other is an example of a peer-to-peer network.

True

A node that supports compact blocks and receives a header or inv message before receiving a block is in what mode?

* Low bandwidth relay mode

* High bandwidth relay mode

* Medium bandwidth relay mode

High bandwidth relay mode

In DPoS, what happens if a block producer fails to produce a block within their designated time slot?

* The block producer is skipped and their economic deposit is slashed.

* The block producer is skipped and immediately removed from the quorum of block producers algorithmically.

* The block producer is skipped and the following block producer produces a block during their designated time slot.

The block producer is skipped and the following block producer produces a block during their designated time slot.