Homework on Blockchain and Mining Visually - Questions

[madingo]

Blockchain and Mining visually answers

1. It is important for blocks to be cryptographically linked to secure the network and its integrity, avoid double spend of utoxs and alteration of previous and present blocks on the network. The new block has reference link to the prior block which forms a chain . Any changes to the blocks will break the chain.

2. The block structure of bitcoin comprises of the following :

• a service ring which is encoded with block header data structure which includes a version field, hash of the previous block, root hash of the Mercle tree of all transactions in the block, current time and the bitcoin difficulty.
• a nonce which is stored in the extraNonce field which is part of the coinbase transaction (a special first block transaction)
• a counter which parameter is small at 32-bits. Each time it wraps, the extraNonce must be incremented (or otherwise changed) to avoid repeating the work.

[Vishnu_Divakar]

1. The integrity and order of transactions soley depend on this cryptographical links. This links ensures that all transactions that happened after geneis block is valid and intact. This ensure that no blocks can get corrupted in between and it ensure a competition for miners to actively work and validate new transaction to add valid blocks to blockchain.

struct transaction {
char *from;
char *to;
char *description;
double amount;
}
struct bitcoin {
long nonce;
long prevHash;
struct transaction *transactions;
};

[jaykake]

1. It stops people from changing data. Transactions are final and data immutability.

2. Data is written in SHA256. Each block has hash based on the hash of previous block, and current blocks hash, and is timestamped.

[Ryanb]

1. Security so that it can not be changed
2. Block number
   Nonce
   Transaction Data
   Hash of the Previous Block
   Hash of current block

[Henry80]

1. Why is it important that the blocks are cryptographically linked together?
   It helps keep the security and integrity of the blockchain with the unique hashes.

2. What does the block structure look like in bitcoin?
   Nonce, the transaction list, the hash of the previous block and the hash of the current
   block.

[giomiri]

1. It’s important because in this way nobody can change previouse block
2. nonce, Transactions, previous block’s hash, new hash

[Perly]

1. This is set up to prevent some one from changing anything in the blockchain. If you change any number in any block all blocks after that block will be invalid since they are linked with hashes, and hashes change depending on the input.

2:

1. Blocknumber
2. Nonce
3. Data (tx)
4. Hash of the previous block
5. The hash of this current block.

[block716]

Answer#1: It’s important for each block to be cryptographically linked together linked-relationship adds security and immutability if someone tries to alter a transaction in a block.

Answer#2: The block structure of bitcoin has the following: 
1. Block Header
2. version
3. Previous block hash
4. Merkle root hash
5. Timestamp
6. bits (Target Hash value)
7. Nounce

[Giorgos]

1. Why is it important that the blocks are cryptographically linked together?
Makes sure that no transaction can be altered, any changes in the block will break all the following blocks. Data is immutable

2. What does the block structure look like in bitcoin?
-nonce -> random number that needs to be guessed
-tx data
-previous hash
-> correct target is required ( difficulty changes)

[ChristopherK]

Blocks are cryptographically linked with SHA-256 to maintain security of each block, so they can not be altered after block creation, only the next block created is update of previous block through consensus, and verified. Thus creating a chain of data inside each block created to the next, connected through the cryptography, data encryption.

[Hosni_Derdour]

1)It is important that the blocks are cryptographically linked together because since the sha-256 is a secure cryptographic hash function , one of its caracteristics is that small changes in input change the whole output entirely, so when someone change some Txs it will result a complet change in the hashs of the blocks , thus the immutability.

2)a block contains :
a-data (Txs)
b-the hash of the previous block
c-nonce
d-the header

[Rui]

1 - To secure the information by ensuring immutability
2 - The block contains the block number, the nonce, transaction data, the previous and the current block hash

[gwen]

• The link is the puzzle created to ensure security and integrity (no double spend)

• The block include the transaction (data), current hash and previous has and the nonce

[derdis14]

@ivan

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

The cryptographic link between blocks is responsible for the immutability feature of a blockchain. A change in a previous block would invalidate the cryptographic link to all following blocks.

@ivan

What does the block structure look like in bitcoin?

• Block size
• A header with meta data:
  – Protocol version
  – Previous block hash
  – Merkle tree hash
  – Timestamp (seconds from Unix Epoch)
  – Difficulty target
  – Nonce
• Transaction counter
• Transactions
  (Source: https://ldapwiki.com/wiki/Bitcoin%20block )

[crypto_dyzl]

1- It is important that the blocks are cryptographically linked together so that any attempt at change a block requires also re-mining all subsequent blocks, which is practically impossible to accomplish.

2- Each block is composed of

• Block size
• Block header: Version, previous block hash, Merkle root, timestamp, difficulty target, nonce
• Transaction counter
• Transactions

[sjbeckm]

1. To ensure security. The blocks are built on links that use the previous hash, transaction list, and the nonce. You break the link, you break the validation.
2. Previous hash, transaction list, and the nonce. Input, transactions, output.

[Effengee]

@ivan

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

This maintains the integrity of the blockchain, as even the slightest change in a single block would also change the entire chain from that block on.

@ivan

What does the block structure look like in bitcoin?

It is composed of the block number, nonce, the data being stored, the previous blocks hash and the current blocks hash.

[Ch_gio]

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

to ensure that data in a block wont get altered easily.

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

Previous block hash, data, nonce and hash of the current block

[lxndr]

Blockchain and Mining

1. Why is it important that the blocks are cryptographically linked together?
   Having all blocks inextricably linked to each other in one continuous chain makes the whole thing tamper resistant against the slightest change in any single block. This setup enables all full nodes to validate the blockchain independently and yet come to the same conclusion (i.e. consensus) as the others.

2. What does the block structure look like in bitcoin?
   According to https://en.bitcoin.it/wiki/Block :

• Magic number (always identical as it identifies the type of the data structure)
• Blocksize
• Blockheader containing
  • Version of used software
  • Hash of the previous block
  • Hash of the Merkle root
  • Timestamp (in UNIX epoch)
  • Difficulty target
• Nonce
• Transaction counter
• Transaction data

[redwolf]

1. This provides network security and eliminates double spend.
2. (block number, data, nonce, hash of previous block) all form new block hash. The energy gone into solving the block forms the chains or “puzzle” solved connecting each block. This is done by guessing the correct nonce beneath the block Target number.