Homework on Blockchain and Mining Visually - Questions

Blockchain and Bitcoin 101
#2251

Nonce is a number used by miners to find a block hash that is below a target. :slight_smile:

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#2252

  1. Why is it important that the blocks are cryptographically linked together?
    This secure the network for integrity. One small change in a block will also change the entire block on

  2. What does the block structure look like in bitcoin?
    Block No. > Nonce > Data > Previous Hash > New Hash

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#2253
  1. By being linked that way a change to a previous block affects every blocks that have or are being mined after that block and that makes doing changes to previous blocks impossible.
  2. The block hash is based on the transactions of that block, the previous hash and a nonce that is randomly found so that the hash is below a specific target. That target is lowered if difficulty increases and higher when difficulty decreases(less miners mining).
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#2254
  1. Why is it important that the blocks are cryptographically linked together?
    To have immutability, security and accountability
  2. What does the block structure look like in bitcoin?
    Linked list
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#2255
  1. To make the blockchain secure. Cryptography allows to “link” all blocks so that one change in any block would break the whole chain down
  2. A block hash is made from previous block hash + transaction list + nonce
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#2256

  1. That is what makes bitcoin and blockchain so magical. If they aren’t cryptographically linked together, we could just go in and manipulate whichever block we want, maybe the others will see the false transaction, but other blocks won’t be affected by it which can lead to ignorance and cause problems. However, having all blocks linked together combined with the rule that the network recognizes only the LONGEST blockchain means if we change something we break the chain, and our block gets immediately discarded because the other miners keep adding new blocks and chains to the network (honest ones).

  2. The block in bitcoin is composed of a block number, hash, previous hash, list of transactions, the nonce that the miners have to guess and many other things.

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#2257
  1. Why is it important that the blocks are cryptographically linked together?
    Because that ensures that the blocks are immutable
  2. What does the block structure look like in bitcoin?
    TX+HASH+NOUNCE
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#2258

  1. It is important that the blocks are cryptographically linked as this makes the blockchain immutable. Any changes to a block will affect all subsequent blocks, this dissuades fraudulent activity and thus ensures data integrity.

  2. A bitcoin block is made up of a block header, transaction counter (how many transactions follow), followed by a long list of transactions (transactions to be recorded in the block). The block header contains: a reference to the hash of the previous block, the difficulty, timestamp, a nonce and the Merkle tree root (data structure to efficiently summerize all the transactions in the current block).

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#2259

Homework on Blockchain and Mining Visually - Questions

Q1: Why it is important that the blocks are cryptographically linked together?
A1: It’s important that they are cryptographically linked as it adds another safeguard against changes in the blockchain. When the block has changed the link between blocks breaks and will have to be mined again.

Q2: What does the block structure look like in bitcoin?
A2: each block is set up with the block #, nonce, data, previous block hash, and the area that will generate the current blocks hash.

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#2260
  1. It ensures the immutability of blockchain by making extremely difficult to adjust a block, as you need to re-adjust all subsequent hashes.

block number + size -->previous block hash --> tx’s --> nonce --> current block hash

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#2261

Homework on Blockchain and Mining Visually - Questions

  1. Why is it important that the blocks are cryptographically linked together?
    Blockchain would loose its meaning if blocks were to become separated. In reality blocks are linked as each next block is confirmed by taking information from previous blocks hash (digital fingerprint of it). It is the foundation of what blockchain is - blocks are chained together and eliminate our ability to go back and alter history of records.

  2. What does the block structure look like in bitcoin?
    There are three components:

  • hash from previous block;
  • transaction list of TX in this block and
  • nonce # that gets mined (guessed).

G.

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#2262
  1. so they can’t be changed
  2. blocks are built using hash from previous block, so if a block changes, they all change, which secures network
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#2263

  1. It’s important that blocks are cryptographically linked together so previous blocks cannot be changed. It increases integrity and trust in the system the longer that it lasts.

  2. The blocks contain the hash from the previous block, the nonce, and all transactions associated with the current block.

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#2264

Most important part is that it has to contain the hash of the previous block as well. Like the first question suggests to cryptographically fuse blocks together so you can’t just change information

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#2265

Yes, The nonce is also a part of it. The nonce is just a random number that miners need to add so that when the whole block is hashed, it is lower than the target. Then it is valid to be accepted by the network. You will learn more about it in the course

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#2266

But a block also has more stuff init. Most importantly block number, hash of the previous block and the transactions that are included.

#2267
  1. The blocks need to be linked together so past transactions cannot be changed without breaking the chain of hashes. If a past transaction is changed the network will reject it because all the following hashes will be changed.
  2. The block structure consists of the timestamp, nonce, difficulty, transactions, previous block hash, and current block hash.
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#2268
  1. This feature of the system is what secures the network. Since subsequent blocks are based on the hash of previous blocks, trying to change something in a block will invalidate its links to other blocks.
  2. Each block contains 5 things: Magic No, Block Size, Block Header, Transaction Counter, and Transactions. The Block Header contains the Version, the Previous Block Hash, the Merkle Root Hash, the Timestamp of when the block was initialized, the Nonce, and the Difficulty Target.
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#2269

  1. to keep the BC network secure, and avoid any attempts of altering or deleting data, that also prevents any miners from attempting to double spend any transaction I believe.

  2. as far as i understood, it would be a hash calculated based upon previous hash, transactions, and nonce…then the calculated hash has to be less than the target set. the target is determined based on number of miners so difficulty is adjusted accordingly. once the hash is successfully calculated and under the set target a link is created " the link also being based on previous block information" and the block is added to the chain.

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#2270
  1. It makes it to where the entire chain of blocks, not one part of one block, could be manipulated without the whole chain being compromised and therefore unable to produce another block
  2. nonce, data, prev hash, new hash
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