Blockchain and Cryptocurrencies

Ztellar · July 8, 2020, 10:26am

I am enjoying this a lot too! I was not expecting the interactive part to be so enjoyable.

Alko89 · July 8, 2020, 4:13pm

I thought you already learned this in the course

Essentially a block contains a magic number (to identify the network and is a constant), blockheader, blocksize, tx counter and transactions.
The hash of the block contains the version, previous block hash, merkle root hash of transactions, timestamp and nonce

carmen1408 · July 8, 2020, 4:31pm

Thanks. If you know can you please tell me in which course is this mentioned? Because some of the words you used are really new to me.

Alko89 · July 8, 2020, 6:32pm

I think the explanation in the course is a bit simplified but still captures the essentials of what goes into a block
I’m not sure if there is any mention of the magic number or merkle trees (tree of hashes) and exactly what parts of the block are hashed. If you really want to learn this in detail you can read chapter 9 in the book Mastering Bitcoin or the Bitcoin wiki:

github.com

bitcoinbook/bitcoinbook/blob/develop/ch09.asciidoc

[[blockchain]]
== The Blockchain

=== Introduction

((("blockchain (the)", "overview of")))The blockchain data structure is an ordered, back-linked list of blocks of transactions. The blockchain can be stored as a flat file, or in a simple database. The Bitcoin Core client stores the blockchain metadata using Google's LevelDB database. Blocks are linked "back," each referring to the previous block in the chain. ((("blocks", "block height")))The blockchain is often visualized as a vertical stack, with blocks layered on top of each other and the first block serving as the foundation of the stack. The visualization of blocks stacked on top of each other results in the use of terms such as "height" to refer to the distance from the first block, and "top" or "tip" to refer to the most recently added block.

((("blocks", "block hash")))((("blocks", "genesis block")))((("blocks", "parent blocks")))((("genesis block")))((("parent blocks")))Each block within the blockchain is identified by a hash, generated using the SHA256 cryptographic hash algorithm on the header of the block. Each block also references a previous block, known as the _parent_ block, through the "previous block hash" field in the block header. In other words, each block contains the hash of its parent inside its own header. The sequence of hashes linking each block to its parent creates a chain going back all the way to the first block ever created, known as the _genesis block_.

Although a block has just one parent, it can temporarily have multiple children. Each of the children refers to the same block as its parent and contains the same (parent) hash in the "previous block hash" field. Multiple children arise during a blockchain "fork," a temporary situation that occurs when different blocks are discovered almost simultaneously by different miners (see <<forks>>). Eventually, only one child block becomes part of the blockchain and the "fork" is resolved. Even though a block may have more than one child, each block can have only one parent. This is because a block has one single "previous block hash" field referencing its single parent.

The "previous block hash" field is inside the block header and thereby affects the _current_ block's hash. The child's own identity changes if the parent's identity changes. When the parent is modified in any way, the parent's hash changes. The parent's changed hash necessitates a change in the "previous block hash" pointer of the child. This in turn causes the child's hash to change, which requires a change in the pointer of the grandchild, which in turn changes the grandchild, and so on. This cascade effect ensures that once a block has many generations following it, it cannot be changed without forcing a recalculation of all subsequent blocks. Because such a recalculation would require enormous computation (and therefore energy consumption), the existence of a long chain of blocks makes the blockchain's deep history immutable, which is a key feature of bitcoin's security.

One way to think about the blockchain is like layers in a geological formation, or glacier core sample. The surface layers might change with the seasons, or even be blown away before they have time to settle. But once you go a few inches deep, geological layers become more and more stable. By the time you look a few hundred feet down, you are looking at a snapshot of the past that has remained undisturbed for millions of years. In the blockchain, the most recent few blocks might be revised if there is a chain recalculation due to a fork. The top six blocks are like a few inches of topsoil. But once you go more deeply into the blockchain, beyond six blocks, blocks are less and less likely to change. ((("transactions", "coinbase transactions")))((("coinbase transactions")))After 100 blocks back, there is so much stability that the coinbase transaction—the transaction containing newly mined bitcoin—can be spent. A few thousand blocks back (a month) and the blockchain is settled history, for all practical purposes. While the protocol always allows a chain to be undone by a longer chain and while the possibility of any block being reversed always exists, the probability of such an event decreases as time passes until it becomes infinitesimal.

=== Structure of a Block

((("blocks", "structure of")))((("blockchain (the)", "block structure")))A block is a container data structure that aggregates transactions for inclusion in the public ledger, the blockchain. The block is made of a header, containing metadata, followed by a long list of transactions that make up the bulk of its size. The block header is 80 bytes, whereas the average transaction is at least 400 bytes and the average block contains more than 1900 transactions. A complete block, with all transactions, is therefore 10,000 times larger than the block header. <<block_structure1>> describes the structure of a block.

[[block_structure1]]

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Hope it helps

if you have any more questions don’t hesitate to ask

Foz · July 9, 2020, 2:00pm

Will Quantum computing be able to break blockchains?

Thoughts?

Ishoboy · July 11, 2020, 4:58am

Thanks Ivan and the whole community.
I’m enjoying so far and learned a lot in this academy.
Excited and looking forward to learn more.

Biggie · July 12, 2020, 4:41am

Not if the nodes are also quantum computers. Which I hear is coming.

Juan · July 13, 2020, 1:31pm

Great course so far.Pretty clear even for a computer dummy like me.Now I feel less dummy.I want to stop just being a speculator and bring something to the table .I do believe that blockchain like this giant truth machine will help us create a better world

andrewb · July 15, 2020, 12:50pm

So far i am very satisfied with the lessons and how they are structured which are a great source of learning. The information received so far this early on in the course is an excellent summery of my prior knowledge and a great addition to a lot of points and facts i was not so clear on.

alcalvillo · July 16, 2020, 9:41pm

Great course thus far! Moving right along consuming the knowledge!

Hector_Martinez · July 17, 2020, 1:09am

By attending these lessons, I feel like i’m at the tipping point towards my goal in the blockchain industry. With every course I complete, I gain greater knowledge.

Bush86 · July 17, 2020, 1:57pm

it seems to help the thinking calm down with the reassuring your on the right track to gaining more knowledge accurately you know you know haha …

TxKidd0572 · July 17, 2020, 3:44pm

The content has been very helpful and interesting. I’ve always been fascinated by technology but never really took the time to really dive in and learn new things. I’ve always been curious about programming and really like cryptocurrency. In May I was laid off at my job and now excited to learn something new will go along with my passion for cryptos.

Thanks Ivan and team for putting this together and sharing your knowledge to help others succeed!

Alko89 · July 17, 2020, 5:18pm

Thanks for the compliment We wish you best of luck on your journey!

_alarming · July 17, 2020, 6:56pm

I am really enjoying this breakdown so far, but it has raised a few questions. I assume they will be answered in future videos, but I’ll ask it anyway:

(1) What prevents malicious parties, or even clumsy humans, from injecting bad or mistaken information into the blockchain? I can conceptualize how false transactions can be prevented on money networks, but (2) what if bad information is put into a blockchain that tracks something like a supply chain/network? (3.1) Does this raise an issue if that information NEEDS to be modified? (3.2) Does one just post a correction to the ledger? Lastly, (4) what issues are raised after, say, two or three decades of information being stored, and single nodes don’t have the drive space to hold an entire copy of the ledger?

Galler · July 17, 2020, 8:07pm

Enjoyed getting a better high level unerstanding of blockchain and its key advantages and solutions to previous problems! Dan

Alko89 · July 18, 2020, 11:27am

Hi @_alarming we love that you are enjoying the courses!
As for your questions:

Depends on what you mean bad information. If information is not in consensus, it will simply be rejected, if the information is correct, but for example a wrong value was sent is another issue and should always be double checked. If you make a mistake by sending someone to much or just set a enormous fee to the miner, it is kind of your fault and no one can help you in this case.

This is a question for the kinds of projects that tackle these issues like supply chains. One of them being OriginTrail. I suggest you check them out and find out yourself

The information can’t be modified, its final. No corrections. If you pay someone to much for example you are at the mercy of the merchant if he/she will send you the funds back.

Hard drive technology is advancing rapidly as all other IT technology out there. There is no doubt there will be large enough HD to store the data that is required to store the entire ledger for decades to come

GalacticBrainBomb9 · July 18, 2020, 9:46pm

hello everyone! thank you for having me!

_alarming · July 19, 2020, 3:53am

Thank you. I’m enjoying it even more knowing that questions get responses

Capig · July 19, 2020, 8:52am

Before starting I learnt a bit about trading and crypto’s and discovered Blockchain in which I had no idea about…
What it meant to me was decentralisation, privacy, trustless and a great asset to adopt in these troubling economic times.
Being the last of the baby boomers I wouldn’t have thought that I would have any interest but soon realised that although being developed 12 years ago to adopt Bitcoin the overall developments being built on top of these platforms are pioneering.
In taking this course, I want to walk away with enough knowledge to implement my own platform or at least have an understanding and direction to work with others who can.
This seams to be a huge step in the right direction.
Time to go hard, cause I ain’t going home!