Building a Blockchain in Under 15 Minutes - Programmer explains

hey what up guys welcome back to my channel and today I have a very special video for you that I think many of you will enjoy because we will namely be building a block chain in under 15 minutes because I want to demonstrate to you guys that block chain in itself is a very simple concept it's a very simple data structure at its core of course cryptocurrencies are complicated but the blockchain is not the reason they are complicated the reason why they're complicated is the consensus algorithm it's the mining is the transactions is everything that is around but blockchain in itself is very easy to understand but you need to know what you need to know before you can actually understand what blockchain is and how it works you need to know what hashes are and you need to know how they work and so a hash is basically a digital signature of of some kind of data so for example I can take a movie and I can hash it and get a digital signature I can take an email and I can hash it and get a digital signature I can take a word and they can hash it I can take a whatever data you just take it you hash it and you get the digital signature for that data so before we start with the actual blockchain let me just demonstrate it to you how this works so we will be building our blockchain in Java it will be very simple and you if you know programming you can do that in another language and if you don't know programming I think you still will be able to understand roughly how this works so let's let's talk about hashes as we can see us we have two lists we have one list that contains ABC and we have a second list that also contains a B and C so this this is the data this is basically the strings we're trying to hash so let's see what kind of what kind of digital signature we will get from list 1 and what kind of so we will just print the digital signature or the hash whenever you hear hash guys you can just think you can replace hash with digital signature so let's see what kind of output we get if we print the Dignitas digital signature of a and signature of at least one and digital signature of least two so as you can see as we get these two numbers and digital signatures are identical for these two lists if I now change anything in list two for example and I run it again you see that I get a completely different digital signature so if I just make a small amendment I just meddle with the data I try to change anything in this list I will get a completely different digital signature and that is the foundation of a blockchain because a blockchain is a list of blocks basically a chain of blocks and each block holds the digital signature of the previous block and the digital signature of the next block is based upon the digital signature of the current block so they are always together the next signature will be based on the current signature and the current signature is based on the previous signature so if you change anything back back in the past you will break all of the signatures they will look completely different and I'm trying to adjust the lighting I should get some kind of artificial light so I don't need to to reduce the window as the light source okay so now that we understand what digital signatures are hashes and digital signatures is basically the same world and how you use them let's actually get into our blockchain coding and let's see if I can make it under 15 in under 15 minutes so the first thing we need to do is talk about our block our block in this case will be very simple it will only contain three things it will contain the list of transactions that happened in that block it will contain the previous hash the hash or the digital signature of the previous block and it will also contain the hash of the current of of itself and this hash will be based on the transactions and the previous hash so if anyone would change anything in the previous block the digital signature of the current block will change and when that changes the digital signature of the next block will change you will see how this works very soon guys so let me just remove this this class that I played around with earlier let me see let me delete and let's start from scratch and we will create a new class and it will be the block so I'm doing it in Java you can do it in whatever language you want it's basically a simple and simple stuff so let's create the fields it will have the previous hash it will have the let me see it will have the previous hash and it will have the transactions list of transactions so I'm just making a a an array of strings so each transaction will be a string in this case of course in in a real block chain the transactions would be their own objects and we will need to create a object for that and define a class and all of that but we're just playing around let's just create let's just create them as strings so and each block will also have a its own hash and this hash will be based on all the transactions let me just define and the array on which we will base the hash so we first of all need to calculate the hash of the transactions transactions let me add an S here and s here and an S here and here and also here so we we will calculate the current hash based on the hash of all of the transactions and the previous hash like this and so the block hash will be the digital signature all the hash however you want to call it of contents and contents are the hash of the transactions that are in this block and the previous hash the hash of the previous block so if I change anything in the transactions or if I change anything in the transactions in the previous block or anything in these transactions in the block before the previous block this hash will be completely different and here you also need to change okay very good guys we have finished our blog let's create the blockchain an ArrayList of blocks so it's basically an array of blocks and ArrayList is just easier to work with let's see blockchain and it will be interesting new ArrayList like this so we need to create orogenesis block because each block chain needs a Genesis block that is hard-coded the reason is because as you can see as each block has the hash of the previous block however the Genesis block is the first block so it has no previous block so we need to hard code how it looks like so Genesis let's call it Genesis block it will be a new block and let's see what kind of things it needs a previous hash which we don't have and it needs transactions so let's just let's just make fake transactions here Tran Genesis transactions transactions and they are equal to for example let's say Satoshi cent Ivan 10 Bitcoin so I'm just writing the transactions as strings of course in a real blockchain this would be some other data structure probably some kind of transaction class but for simplicity let's just let's just write them as strings send ten bitcoins to Ivan so everyone is sending me Bitcoin in this Genesis block so I add it like this so guys now we can actually output the get block hash let's see I need we need to create a getter for the block hash so now we can actually output now come on yes now we can actually output the digital signature of the block we just created block hash let's see what it looks like so as we can see I get this number there is a negative mind something so this is a digital signature of this block that we just created now if I change anything at all in this block let's say that I want I want to cheat the system and I suddenly say that Satoshi sent me a million Bitcoin or like 100,000 Bitcoin and if I run this now we will see that the digital signature is completely different and this is very important because when we create our second block let's say block let's create our second block it will need the first of all it will need the previous hash it will need the hash of the previous block and that is the Genesis block blockchain hash and it will need some kind of transactions I see let's say that block two transactions let's say that in the second block Ivan sent ten Bitcoin to Satoshi I sent him back his bitcoins and Satoshi sent ten Bitcoin to Starbucks like this so these are the transactions in the second block so yes as you can see if I put the transactions and we output now the digital signature of the second block let's just do like this hash of block two hash of Genesis block so now we can actually output the hash of block 2 and the Genesis block something is ok I forgotten you let's see let me shrink myself here so as we can see hash of the Genesis block is this number Hacha block - is this number now yes here is the interesting part that if I change anything in block 1 for example let's say I suddenly say that Satoshi send me this many bitcoins and they run it you will see that these numbers would be completely different as you can see the hash of Genesis block is completely different and the hash of the second lock is completely different and so this is the basic foundation of the blockchain that if I change anything back here the next block will get a completely different signature and that is because we're passing the previous hash and group and we are calculating the current hash based on the previous hash and these transactions so if I change anything in the past the transactions will be different the hash of the transactions will be different and this change will propagate through the blockchain and so let's just create a third block like this let's say block 3 transactions and block 3 and now we have the previous hash will be block 2 block 2 and the transactions will be block three transactions and let's say that in this block I will I sent one Bitcoin to my mom like this or let's give her this many bitcoins and if I get the digital signature of that let's see block 3 like this and we'll run it I get the following I get the following signatures so I just want to demonstrate not to you guys now that if I change anything in the first block let's say that I add this a I just change it change anything in these strings in these strings as you can see it's completely different the signatures in all of these steps and this this hashing algorithm is is very hard to crack and the more blocks are created on top of of the of one block the transactions in that block are more and more confirmed because it's harder and harder to crack all of these hashes because the previous hash will be based on the hash before that and the current hash will be based on the previous hash and so as you can see a change in any of these transactions in any of the data in the one block will propagate and change all of the digital signatures in the future and that is how abduction works because if I change something everyone else will see that my digital signatures are completely different from everyone else's so that means that I have cheated so if I just tell everyone that hey Satoshi gave me this many bitcoins back back then and here is the blockchain that that confirms that everyone will take a look at it and say well I will know this blockchain doesn't confirm that because we have our own versions of the blockchain and the digital signatures are completely different so guys I hope you enjoyed I hope you understood the basic concepts of hashing of of linking blocks together via their digital signatures or the hashes and if you are new viewer and you like blockchain technology theorum programming software development you should definitely subscribe to this channel guys because you will find it interesting I myself am a software developer and I'll see you guys tomorrow I hope you really know how blockchain works and how the concepts behind it have a good day guys goodbye

Channel: Ivan on Tech

Views: 651,004

Rating: 4.8840618 out of 5

Keywords: bitcoin blockchain, ethereum blockchain, bitcoin, ethereum, cryptocurrencies, blockchain, crypto blockchain, Building a Blockchain in Under 15 Minutes, programming blockchain, blockchain programming, Programmer explains, ivan on tech, java programming blockchain, blockchain from scratch, iota, nem, neo, lisk, eth

Id: baJYhYsHkLM

Length: 14min 28sec (868 seconds)

Published: Thu Aug 31 2017

Reddit Comments

[u/TokenBnk]

Ivan is definitely the most knowledgeable crypto youtube personality in my opinion. This video's great. No better way to understand a technical concept than to explain the code in layman's terms.

[u/Moose793]

I have no affiliation with Ivan. I am a fan though.

At first, I thought he was just another loud mouth trying to capitalize on blockchain and make money off being an undeserved thought leader.

Then I did some digging and found out this guy has a masters degree in computer science and has worked as a developer for years. He actually knows his stuff, and I enjoy his channel.

Check him out.