Question

Problem 1

Which of the following information is specified by a bitcoin transaction:

A. A number of inputs (coins being consumed ).

B. A number of outputs (coins being created).

C. The user's account balance.

Problem 2

In a Bitcoin transaction, which of the following statements is INCORRECT when Alice wants to pay Bob 19 bitcoins to Bob (given the output she owns is worth 25 bitcoin):

A. Alice needs to create a new output where all 25 bitcoins are sent to Bob.

B. Alice needs to create a new output where 19 bitcoins are sent to Bob and 6 bitcoins are sent to herself.

C. Alice needs to create a new output where 6 bitcoins are sent to Bob and 19 bitcoins are sent to herself.

D. Alice cannot use bitcoin to pay Bob now. Alice needs to wait until she makes another payment to Bob. Then, the two payments can be combined.  

Problem 3

Which of the following statements about the Bitcoin scripting language is INCORRECT:

A. The scripting language is stack-based.

B. Every instruction is executed exactly once.

C. Loops are allowed in the Bitcoin scripting language.

Problem 4

Which of the following statements about the CHECKMULTISIG is INCORRECT:

A. This is one of the basic instructions in Bitcoin scripting language.

B. It let you check multiple signatures with one instruction.

C. It requires specifying n public keys and a parameter t. For this instruction to execute validly, there have to be at least t signatures from t out of n of those public keys that are valid.

D. Currently, there is no bug that can be found in CHECKMULTISIG.

Problem 5

Which of the following statements about the Bitcoin network is INCORRECT:

A. It is a peer-to-peer network.

B. There are special nodes in the Bitcoin network, e.g., master nodes.

C. Each node peers with other random nodes.

D. New nodes can join at any time.

Problem 6

Which of the following statements about fully validating nodes/lightweight nodes in the Bitcoin network is INCORRECT:

A. Fully validating nodes must stay permanently connected to hear about all the data.

B. Fully validating nodes must store the entire blockchain and need a good network connection to be able to hear every new transaction and forward it to peers.

C. Lightweight nodes only store the pieces that they need to verify specific transactions that they care about.

D. A lightweight node has the same security level as a fully validating node.

Problem 7

Say Alice and Bob want to do business with each other — Alice wants to pay Bob in Bitcoin for Bob to send some physical goods to Alice. The problem is that Alice doesn’t want to pay until after she’s received the goods, but Bob doesn’t want to send the goods until after he has been paid. As a solution, we introduce a third party (Judy) and do an escrow transaction using MULTISIG.

Specifically, Alice creates a MULTISIG transaction that requires at least two of three people to sign in order to redeem the coins.

1) When both Alice and Bob are honest (Bob will send over the goods to Alice and Alice will pay Bob after then), briefly explain how this transaction is completed using MULTISIG. Does Judy need to get involved?

2) What if Bob is malicious, i.e., he doesn't want to send the goods to Alice and refuses to sign a transaction that releases the money back to Alice? Does Judy need to be involved? How can they use MULTISIG to help Alice get her money back?

3) What if Alice is malicious, i.e., she refuses to pay after receiving the goods? Does Judy need to be involved? How can they use MULTISIG to help Bod get the payment?

Answer 1

1. c users account balance.

2.

A. Alice needs to create a new output where all 25 bitcoins are sent to Bob.

C. Alice needs to create a new output where 6 bitcoins are sent to Bob and 19 bitcoins are sent to herself.

D. Alice cannot use bitcoin to pay Bob now. Alice needs to wait until she makes another payment to Bob. Then, the two payments can be combined.  

3.C. Loops are allowed in the Bitcoin scripting language.

4.D. Currently, there is no bug that can be found in CHECKMULTISIG.

5.D. New nodes can join at any time.

6.D. A lightweight node has the same security level as a fully validatin nodes

7.1.judy needs to be involved

1. alice and bob agree to terms - Either the Buyer or Seller begins a transaction. After fulfilling certain rules, all parties agree to the terms of the transaction.
2. Buyer pays judy - The Buyer submits a payment by approved payment method to our secure judy Account, judy verifies the payment, the Seller is notified that funds have been secured 'In judy's account'.
3. bob ships merchandise to alice - Upon payment verification, the Seller is authorised to send the merchandise and submit tracking information. judy verifies that the Buyer receives the merchandise.
4. alice accepts merchandise - The Buyer has a set number of days to inspect the merchandise and the option to accept or reject it. The Buyer accepts the merchandise
5. judy pays the bob - judy releases funds to the Seller from judy

7. 2.judy needs to be involved here judy should collect the money from alice and keep the money until she gets the required quality goods.if alice is not satisfied with the product money will be released to alice..and product will be returned to bob.if she is satisfied then money will be given to bob.

7. 3.same as above step

Answer 2

Problem 1-

Option is incorrect because Bitcoin doesn't track account balances like traditional accounting, it only keeps a record of where BTC came from and which address it is sent to. So, your receiving address doesn't technically have a recorded balance, only a calculated balance for all the transactions received on that address.

Problem 2-

Option D is incorrect because it is not written anywhere that you have to make 2 transactions.

Problem 3-

Option C is incorrect because there are no conditional statements and no loops.

Problem 4-

Option D is incorrect because it never shows the nill bugs.

Problem 5-

Option B is incorrect because There's no hierarchy, there's no centralized, special nodes, no master nodes. Every node on Bitcoin is an equal peer. It runs over TCP, it has a random topology, so there's random nodes are peered with random other nodes. And new nodes can come at any time.

Problem 6-

Option D is incorrect because they are not having same level of security.

Problem 7-

1. No, judy not need to involved between two of them because Multisig is short for multi-signature, a lock that only opens with enough keys, out of a set of predefined keys. ... So,they each get one key and use a multisig wallet that requires two out of three of those keys. They both have to be honest for each other.

2. no, there is no need of judy's involvement as Alice creates the multisig address from her own public-private keypair and two public keys from Bob. If Bob wants to 'finalize early' he can broadcast a signature with both his keys beforehand. The precommitment idea is that the coins can be confirmed waiting at a multisig address with one signature from Alice also confirmed and the only thing that needs to be confirmed after that is the network seeing a signature broadcast with one (or both) of Bob's keys.

3. Again, there is no need to involve judy in the matter. Read carefully point 2 is related to this answer.