Homework on Blockchain and Mining Visually - Questions

[Ribr]

1. Why is it important that the blocks are cryptographically linked together?
   It is important that the blocks are linked together to secure the blockchain and prevent anyone to alter any data in a previously mined block. Any change would break the link between the current block and the previous one.

2. What does the block structure look like in bitcoin?
   Block number, Hash of the previous block, all the transactions of the current block, the nonce (random number)

[John12]

1. It makes it practically impossible to change a transaction after it is added to the blockchain, because all blocks after the one that is changed would have to be remined, otherwise their cryptographic links will remain broken and invalid.

2. transactions, a hash of the previous block, and a nonce that must be guessed in order to generate a hash value that is less than the current target.

[scuderia992]

1. Why is it important that the blocks are cryptographically linked together?
   A. To make it difficult if not impossible to corrupt the chain as changing one blocks impacts all the blocks before it. The transactions cannot be reversed in previous blocks.

2. What does the block structure look like in bitcoin?
   A. Hash, Previous Hash, Transaction list, Nonce

[Timschi]

• 1 The cryptographic link increases security. By changing something in one block all subsequent blocks wouldn´t match anymore.
• 2 The blocks contain the following information:
  -Block Size
  -Block Header
  -Transaction Counter
  -Transactions
• The Block Header contains the following information:
  -Version
  -Previous Block Hash
  -Merkle Root Hash
  -Timestamp
  -Difficulty
  -Nonce

[jonnybjj]

@ivan

Homework on Blockchain and Mining Visually - Questions

1. Why is it important that the blocks are cryptographically linked together?
2. What does the block structure look like in bitcoin?

1- Cryptography ensures the security of the blockchain. Nothing can be edited with out making the chain invalid.
2- The block includes the hash of the previous block, transactions of the current block, and nonce that is calculated.

[birdie]

1. It is important that the blocks are cryptographically linked together because then any changes are obvious and affect all other blocks.
2. The block structure of bitcoin includes a nonce, the hash from the previous block, and transactions to be added to the blockchain.

[The08th]

1. Why is it important that the blocks are cryptographically linked together?

• So that if any data is changed in one of the blocks each subsequent block will also have it’s hash changed .This ensures the authentic blockchain is always verifiable by the network except in the improbable case of a 51% attack.

2. What does the block structure look like in bitcoin?

• Each block contains a list of transactions, a nonce and the hash from the previous block. A unique hash for each block is calculated using the SHA256 algorithm which uses the hash from the previous block, transactions in the current block, and a random number called a nonce which is used to ensure the current block’s hash is less than the target hash assigned by the mining algorithm.

[hwbrill]

1. so it is impossible to go back and change data…
2. Block’s hash is derived from Data + previous block’s hash + nonce

[Pogchamp]

1. Why is it important that the blocks are cryptographically linked together? | Because otherwise to change a block already added to the blockchain, you would only need to re-mine the block you’re trying to change, and not the blocks in front of it.

2. What does the block structure look like in bitcoin? |

[Vladimir.B]

1. Why is it important that the blocks are cryptographically linked together?

   So that one block could not be changed without changing all the blocks that come after it, making it a very secure system.

2. What does the block structure look like in bitcoin?

   [ “data” + “prev hash” + “nonce” = “hash” ] ===>[ “data” + “prev hash” + “nonce” = “hash” ] ===>

[R_G]

1. This is to ensure that data in the blockchain are immutable.

2. The current block’s hash is made up of transaction list ,nonce and the previous hash.

[nutrina]

1. Why is it important that the blocks are cryptographically linked together?

Security. You cannot change a block without damging all following block links.

2. What does the block structure look like in bitcoin?

• transactions
• nonce
• previous block link

[Alko89]

@Pogchamp

What does the block structure look like in bitcoin? |

What happened to the second answer?

[CyberYeti]

1. It is important that the blocks are cryptographically linked together because this helps to ensure that it becomes practically impossible to change/alter previous entries. This makes the network safer. Not only would changes be immediately noticeable but it would be near impossible for the bad actor to ever catch up and change the rest of the block fast enough to get away with anything. The addition of cryptography makes this aspect more challenging for the computational power and resources needed (time, power, etc) are all increased.
2. The block structure in bitcoin looks like a string of blocks (current and previous) complete with the nonce, previous transactions, previous hash, and resultant new has for the current block. Each block demonstrated has all these four features: nonce, transactions, previous hash, current hash.

[OlgaB]

1. It is important that the blocks are cryptographically linked together in order to prevent the possibility to make changes on older blocks (altering data)
2. The block structure in a bitcoin consists of: previous hash, list of transactions and nonce (random number that miners need to find)

[888]

1. This allows for all data on the blockchain to be immutably linked

2. A block is constructed from the previous hash, the data to be added to the blockchain and the nonce, all hashed together to create the hash for the next block.

[CryptoBee]

1. Why is it important that the blocks are cryptographically linked together?
   So that no transactions can be changed in the previous blocks. (easily or efficiently, it is possible. Probably.)
2. What does the block structure look like in bitcoin?
   Hash of Previous Block, Current Block’s Hash, Data, Nonce.

[frankiewalters]

1. One very important feature of blockchain is its security. Part of the security is the fact that it is next to impossible to rewrite or change, or erase anything that is already put into script on the digital stone (block). To cryptographically link these blocks together means that one slight change anywhere in the already made blocks, will signal a whole rewrite/rehash for all the blocks linked to it; to cryptographically link the blocks together gives anyone who dares to change something a herculean task of re-mining the whole blockchain, otherwise render it all invalid.

2. (page from my notes)
   

   

[DaJoker]

I actually thought I understood what a merkle tree is supposed to be. I get that it is a tree of hashes, but where do the hashes come from? Aren’t those the UTXOs that are encrypted with sha256? Am I confusing things now?

[Alko89]

@DaJoker

I get that it is a tree of hashes, but where do the hashes come from? Aren’t those the UTXOs that are encrypted with sha256? Am I confusing things now?

They are the transaction hashes which are also used as ids (txid). UTXOs are transaction outputs and are included in the tx data so they are hashed with the transaction (or the unlocking script hash in case its a segwit tx).
These transaction hashes (or txids) are then used as the leaves of the merkle tree. The root of the tree is then used in the block hashing process.