Blockchain Full Course 2026 | Blockchain Tutorial For Beginners | Blockchain Course | Simplilearn

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course on blockchain fundamentals by simply. Let's kick things off with a little secret. You have probably heard people saying blockchain is just a trend, but the truth is blockchain is changing the world. From cryptocurrencies to supply chain management, blockchain technology is in high demand and it's not going anywhere. By the end of this course, you will have a solid understanding of how blockchain works and how it's used in various industries. So whether you want to develop blockchain apps or just understand cryptocurrencies, this course has got you covered. So here is what we'll cover in today's video. First, we'll understand what is blockchain. We'll cover what blockchain is and how it works. Next, we'll have a look at applications of blockchain where we will discover real world applications like cryptocurrencies and supply chains. Next, we'll understand the difference between public versus private blockchains. We'll also learn about mining and how proof of work validates transactions. Next, we'll explore the more energyefficient proof ofstake method. We'll also understand gas fee and how they affect Ethereum transactions. We'll get practical tips on building wallets, smart contracts, and tokens. Also, if you are looking to dive into blockchain technology and want to start with the basics, I have got something exciting for you. Check out this free blockchain course that comes with certification. This course is designed to give you hands-on experience with blockchain fundamentals like Bitcoin, Ethereum, smart contracts, and much more. So whether you're just a beginner or looking to expand your knowledge, this course is perfect for you. You will get 6 hours of self-paced lessons plus 90 days of free access to all the content. And yes, once you complete it, you will get a completion certificate to showcase your new skills. So, if you are ready to explore how blockchain is changing the world of cryptocurrency and beyond, why not get started today? It's all completely free and it's the perfect first step to the world of blockchain development. So guys, before we dive in, here's a quick quiz question for you. The question is, which of the following best describes blockchain technology? Your options are a system for managing digital identities, a decentralized and transparent ledger for recording transaction, a traditional banking method, a type of cloud storage for data. Take a moment to think about your answer and once you're ready, we will get started. As of now, you see in the Bitcoin what we know in the Bitcoin, we already know about roofer work. One case, we know about the halfing concept. What is halfing? So now in this case you see halfing is also one of the uh concern and then we have limited supply of bitcoins. This is also we understand also we understand what is bitcoin minting. Okay. Now all these concepts we know and also I should write here the difficulty adjustment as well. difficulty adjustment and also we know about the case of nons as well. So nons is number that is used only once a random number. Now one more thing that we are using this is utxo and believe me this is you know um uh I have seen many interviews where this question has been asked by the by the interviewer or the recruiter. So you should know this concept very well and we'll I promise you we'll be covering it in very easy language so that all of you have a very good understanding of this. So now you see I'm saying unspent transaction um output. So what is the full form or what is the abbreviation for this unspent transaction output? You see here UTXO. Okay. And now when I say UTXO what exactly is this? Now to understand this let's understand a uh I can say a imaginable scenario or a real life scenario. Now let's say I do have a note of 500. All of you listen this carefully. I do have a note of 500. In fact I do have a note of 500 three notes. So how much is my total amount? How much is total amount? So we are talking about fiat currency Indian rupees. So this is my physical currency and once we understand that then we'll come back to the physical currency. So total amount is what? 1,500. Okay. So I do have a 1,500. So I entered into a grocery market. So my total bill is 1,200 and I do not have any other amount apart from this and plus I am not paying anything online as well for certain reasons. No GPA, no UPI, no card payment, nothing is there. So how I will make the payment? How I will make that payment? I do not know. I have 500 notes. Total 1,500. So how many notes I should be giving to the shopkeeper? >> Sorry. How many notes I should give to the shopkeeper? All three. All three notes. Because we know 500 multiply 3 is500. So I cannot go with two also. I cannot go with the uh one also. So I will be giving total all 500 into three. So with respect to this the shopkeeper will be giving me a change. Okay. Change. Now how much will be the change? So this will be 300 rupees. Correct? Okay. So this 300 rupees the combination could be u a note of 200 or note of 100 or maybe the combination could be a note of 100 a note of one more 100 or a note of 100. Okay. So this could be possibility or even any number of combinations could be there. We we can just consider anything. So basically now you see these things I give a name. What name I'm giving? Input is or I can say input is 1,500 or in this case I'll take 500 3 500 into 3 only. So input what I have given to the shopkeeper three notes of 500 what I am reing as output what I'm receiving as output one my item or when I say what is whatever I have shopped for plus I am getting 300 rupee change okay what I'm getting 300 rupee change now note this term this is what 300 this is my change that I received after my shopping okay now in this case As you see when I say 300 as a change so I'm associating this 300 with unspent transaction output. Correct? But now you will be thinking Bitcoin is not about any physical money. Bitcoin is all digital. So why do we are talking about change in something? But you see this is the beauty of the concepts. Now Bitcoin how do they follow the things? Let's consider this. So they follow the UTXO model. As of now, they follow the UTXO model. And uh when you understand this, you will also find that why they are following up this complicated method. But uh for certain reasons, Bitcoin is falling up. So when I say UTXO model, let's say I am this is I am Alice. Alice account balance is 10 bitcoin. Okay. Ellis 10. Uh, let me take it like this. Alice and Bob. Alice account balance is 10 bitcoin. Bob's balance is 5 bitcoin. Okay. Alice and Bob we have taken here. Now what is the target? Ellis is willing to transfer some amount to Bob. Okay, that is well taken. Now when I say 10 bitcoin, this 10 bitcoin is not like a digital money. 10 bitcoin is not like a digital money. It is more like a physical money. How? This is being arranged into components. What is that component? So might be you see one component is five bitcoin, one component is two bitcoin, one component is 1 bitcoin, one component is 5 + 2 is 7 8 and 2 bitcoin is it making total 10? Is it making total 10? 5 + 2 is 7. 7 + 1 is 8. 8 + 2 is 10. So total is 10 bitcoin. Okay. So now what I have said as of now as of s now now I have just given you a situation that we have two user one is Alice one is Bob Alice account balance is 10 bitcoin Bob's account balance is 5 bitcoin and then I mentioned bitcoin is also maintaining some components to form a total account balance. So this is we have taken a shape of company. Okay. Now similarly the same thing should be applied to the Bob as well. So let's say component for Bob is three bitcoin plus two bitcoin. Okay. Now the case is Alice is willing to transfer Bob money of I say here two bitcoin or in fact four bitcoin. Correct. Now you see from this component which component should be passed to the Bob. In fact rather than making it four I make it something called as six or I make it 6.5. That will be better. Okay. Now you see so Alice wants to transfer Bob 6.5 bitcoin. Choose the component and let me know how would you proceed. Just thinking about your physical money which component you will choose. Ultimately this program has to be done by the this uh this conversion or the selection has to be done programmically but as of now we are considering it so we are solving it. So which component or which combination should be chosen? 5 + 2 others also see 5 + 2 or anything else I should try which component we should choose 5 + 2 5 + 2 correct. Now you see if we go with this 5 + 2. So what we are transferring to this five bitcoin plus 2 bitcoin and once this transaction has been made. Now you see these two components are reserved. These two components are reserved. Once the transaction is verified how much change will be coming to the Alice? Once the transaction is verified, how much change will be coming to the Alice? How much change will be coming to the Alice? 0.5. 0.5. So we can say that this is my UTXO unspent transaction output. This will be 0.5 bitcoin. So what will be the updated balance of Alice and Bob? Calculate the balance. What will be the updated balance of Alice and Bob? So you see Alice was having what? 10. So we transferred 6.5. So balance should be 3.5 bitcoin. What about Bob? How much will be the balance? What about Bob? So 5 + 6.5 is 11 uh this was 11.5 11.5 bitcoin. And if I talk about the components now, if I talk about the components earlier it was available. So can I say that this is being replaced by 0.5 bitcoin. And what has been achieved from this? This is 5 bitcoin plus 1.5 bitcoin. Is it happened like this? Is it happen like this? Check check my component theory. Is it correct or should we change something over there? See what happened into this case. This I was transferring I was transferring what I have taken one component from this. Okay. Transferred two bitcoin transferred but we have got a change also that change is what 0.5 bitcoin. So one bitcoin remaining same two bitcoin remaining same. There this person has got what? three bitcoin plus 2 bitcoin and then I have 5 bitcoin plus 1.5 bitcoin so this way we are giving up here does Bob return 0.5 uh Sanjie in this case so whenever we say the component is designing so program is able to convert that two bitcoin to 1.5 bitcoin so now you see in actually whatever we are talking do we have any physical currency Do we have any physical currency? No, we we are not having any physical currency. Everything is according to a program now. But how this Bitcoin is making it sure they have used Bitcoin scripts to manage the component over there. And what is the reason of this complication? It could have done like a normal subtraction also. It could have done with a normal subtraction also. So they wanted to make sure there is no double spending problem. Now what is double spending problem? What is double spending problems? So we know that in Bitcoin average time for block confirmation is what? How many minutes? How many minutes? 10 minutes. So in that 10 minutes you see let's say now my when my account will be updated this 10 bitcoin when my 10 bitcoin will be updated right now my balance is 10 bitcoin when this will be updated can I say that after the block confirmation can I say that after block confirmation yes after 10 minutes. So meanwhile if I am using my all the balance and I might use something like a double spending problem also in actual I have already spent five bitcoin again I'm trying to you know change that and that logic is just checking my balance over there by arranging into the component. So they are trying to solve the problem of double spending and that is why they are using what utx model. Let me explain again here. So why what we are doing? So basically UTX is the equivalent to digital form of change. Correctum correct. Yes. This is the correct thing and very well spoken about this. So you see here what I'm trying to say. We have taken example that we have two user. One is Alice, one is Bob. Alice initially having balance of 10 bitcoin. Bob is having five bitcoin. So this time we are not having the total account balance like this. The whatever is the balance this is being arranged into some partitions some components and it could be anything. And how it is different from you know physical money like in physical money we have certain type of modes like only 500 only 100 only 200. So in this this is not like that. So there are programs where they are working into the same scenario to generate the components. Whatever is the component it is coming to the users. Now we have taken that Ellis is willing to transfer 6.5 bitcoin. So what we have chosen from this five bitcoin and 2 bitcoin and this is being sent to Bob. their program is working and this program is making sure that 0.5 bitcoin is returned as a new component for the Alice. So that is why the balance is being updated as 3.5 bitcoin and 11.5 bitcoin and ultimately we do have such arrangement over there. Okay. Uh where is these components are stored when this will be stored into my wallet only. So let's say I created my account on the binance and this is my wallet. So it will be stored into the same place. How the initial components are decided say for Alice uh 10 bitcoin breaking it to various denominations. Rajes so whenever u I got this denominations or whenever I received it so it was through the same let's say somebody transferred me 10 bitcoin as you are taking into the example. So this component is coming to me into some kind of form. So that form is directly coming to me. So whatever was the denomination that is coming to me. Another case you see when the minting is happening the bitcoin is minted. So that time the component is 3.125. That time the component is 3.125. Let's say I transfer to somebody else. So maybe I'm transferring this from this. I'm transferring 1 to5. From this I'm transferring 0.125 bitcoin. So what is the next component for me? What is the next component for me? Three bitcoin. Can I say that? Can I say that the next component is three bitcoin for me? Correct. Correct. Now let's see more examples there. More examples because we need to understand like this. Let's say Alice is new to the Bitcoin community. Okay, that time she purchased from somewhere and when she is purchasing that time again the component has to be come through whatever is the community giving. So let's say she just p say p p p p p p p p p p p p p p p p p p p ppurch purchase one bitcoin as of now. Next time her friend is transferring her 2.3 bitcoin. So this way the component will be arranged. Now when she is transferring somebody, let's say she wants to transfer approximately three bitcoin. She wants to transfer approximately three bitcoin. So she will be left with what? She is using one bitcoin component as well. 2.3 bitcoin component as well. What she is transferring three bitcoin. What will be the balance for her? What will be the balance for her? 0.3 0.3. So can I say that a new component is generated for her? Can I say that a new component is generated for her? Uh V. So all the components have UTXO label with them in wallet. Correct V. Correct. Correct. Do you understand the UTXO model? Now all of you very simple concept. Uh now give your thoughts on to this. So what is logic? Because transactions also can be traded. So it is based on single transaction denomination. For example, if I bought one bitcoin, 0.5 bitcoin, 0.25 pair. So three denominations for me. Correct. Rajes. Correct. So don't you think they're increasing the complexity into the system? Don't you think Bitcoin is increasing complexity into the system? And uh the reason behind is that because the time period that we are considering that is very very high 10 minutes is very high time. So that is that is only you know one uh one thing we we can say that this is making them efficient for uh double spending problem. Okay. Uh so what is logic? Because fractions also can be traded or it is based on single transaction denomination. Uh Rajes can you please unmute yourself? I think it is better we interact then we can understand this. So hello. >> So I'm just saying that uh this is for the example which you have taken five uh 532 just an example correct >> but these transactions are happening. So denominations are not fixed. So idea is not about the replica of real money transactions of fixed denomination. >> So this is basically whatever you're transacting because it's in fractions also right you can buy 0.05. >> Yes. Yes. How many transactions are there in operations? Right. >> Correct. Correct. So this changes or UTX or whatever we are considering this only happens at the time of when say the change is coming. So that time they have not kept it okay. Uh like physical money we are fixing some kind of amount. This is not required into this case and they're just trying to solve one problem that is our uh what we can say double spending problem. And only the reason they are taking it because their uh their block confirmation time is very high. So this is one of them. They have taken many step. This is one step into a part of the same double spending problem. Uh Ashwin so when I have to get the total balance for a person do we need to add uh okay uh Ashwin this is not our responsibility. So wallet will be automatically doing it. It is showing me the total balance only. But when I see that I can see all that you know fractions as well. So it will be automatically calculating for me. Uh Rajes do you want me to unmute if you're left with something? Okay. Okay. Thank you. Uh Ashwin you got the clarity onto this? See in case you have any question uh anything you you have some doubts it is better to discuss rather than sitting like that only then we can understand that what is uh what is the level of understanding of for each other yes ashwin we can we can take a one more example for this see what is double spending problem let's say this is I'm having 10 bitcoin or I take less amount here okay so I take five bitcoin so this is Alice this. So we know that block confirmation happens only after 10 minutes. Okay. So what I did I transferred five bitcoin once I transferred five bitcoin one more time. I transferred one more time. This is five bitcoin. Okay. Now you see I have only five. But what I'm trying to do here, what I'm trying to do here, how how much transfer I'm trying to do? Can I say that 15 bitcoin and you will be asking how it is possible? It is possible. My account is still not updated. I just created the transaction. I submitted it to the unconfirmed transaction pool and now it is still with the uh waiting for the verification. This is with the minor or this is you know sitting or this is into the unconfirmed pool. But what I tried here obviously it will be stopped at the minor over side but you are increasing what you're just increasing the complexity into the system. So Alice tried to transfer how many times? Three times with the what total amount causing a 15 bitcoin. Now if I say this component that it is entirely being freezed this component is entirely being freezed. So this freezing is giving the power that this cannot be reused. Okay. Now I take one more example. Let's say Alice is having one more bitcoin. Alice has having one more bitcoin. Now she did what? She tried what? She tried what? This particular bitcoin to transfer at one side. Now if we follow the utxo model, this has been reserved. Reserved means I cannot use the component. But can I use this component? According to the UTXO model, can I use this component? Yes, I can use it. I can use it. So when I'm using this, this again become reserved over there. So now you see these two components are into the reserved side. So when it is into the reserved side, I cannot do the double spending. I cannot create the fake transactions here. I cannot create the wrong transaction here. So that is why the double spending problem is solved at a certain level. Another case you see another case you see uh let's take one more example in this case what is happening here this is case of what one bitcoin 5 bitcoin 1 bitcoin and two bitcoin now in this case I just want to transfer what one is five bitcoin then I want to transfer one bitcoin and then I want to transfer 0.5 bitcoin Okay, see this this very carefully I I want to show one more thing here. And then I want to do 1.5 bitcoin. Okay, this I want to transfer. So this is my let's say this is my transaction one. This is my transaction two. This is my transaction three. This is my transaction four. Okay, the sequence I'm also following up. Will it be okay? Can I do that five bitcoin according to the UTXO model? Can I do that? Five Bitcoin. Five Bitcoin. Can I do that? Yes, I can do that. One Bitcoin. I can do that. Two Bitcoin. This is for what? 0.5 Bitcoin. So now tell me, can I make the transaction four? Can I make the transaction four? No. Can I make the transaction four? No, I still have my account. I still have my amount. See, five bitcoin reserved. One bitcoin reserved. Now you see two bitcoin is also reserved here. 2 bitcoin is also reserved here. I need to wait for next 10 minute once I get my change then I can do the 1.5 bitcoin. Right? Have you understood this or I should explain this uh again. I'll come back to the questions everyone. I'll come back to the questions. Have you understood this? See what what we are trying uh trying to say here. I have some amount. Okay, it is solving my double spending problem also. But sometimes it may happen that I still have the amount just because my transaction is not verified still I cannot use it. So that is also a possibility here. Uh yes see what we considered here uh Manisha that we have component like five bitcoin, one bitcoin and 2 bitcoin that is making my total as 5 + 1 6 + 2 is 8 bitcoin. Okay. Now what kind of transaction I want to do? So in transaction one I want to transfer to Ram. Transaction two I want to transfer to let's say sham. Transaction three I want to transfer to Bob. This I want to transfer to U some XY Z guy. Okay. So now in this case you see this is my transaction one. Second one. Transaction two. Transaction three. Transaction four. Total amount which I'm trying to transfer. This is five + 1 is 6. 6.5. And total the same amount I want to transfer. I want to you know uh nullify my balance. Now in this case you see I made transaction one. This component reserved I cannot reuse it. I transferred one bitcoin. This component become reserved. I cannot reuse it. Again I made a transaction. This is transaction three. In this case I was trying to transfer what? 0.5 bitcoin. I'm only left with what? Two bitcoin. So now this is also reserved. I have next transaction. So this is transaction of 1.5. Logically I have the balance. But if you follow the UTXO model, my all components has been become reserved. So when it is reserved, this two bitcoin has been reserved. I cannot reuse it unless the block confirmation happen. When the block confirmation happen for this transaction three, what I will receive? I will receive a UTXO. That UTXO will be of 0 or in fact 1.5 bitcoin. Once I receive this component, then I can make this transaction. Correct? Uh Manisha, do you understand this now? Uh Manisha, do you understand this now? Okay, now let me come back to the questions. How is it flagged as reserved when the block has not been updated till 10 minutes? Ashwin see whenever I use it, this is being flagged. Whenever I'm using it, it it becomes flagged at that same time. Uh Jaganath, what Alice has 20 bitcoin but she transferred three times five bitcoin into three times. So in that case uh jagernad this also depends on the component. If component is trying if component is having the same thing that is okay. If component is allowing the same thing that is okay. So with this theory say I have two component five and five total 10 I put a transaction of 7.5 bitcoin and then I want to transact 2.5 I can't do the second or as both component is block correct correct Raj. So I was explaining this only and you have rightly said this and then do we have any kind of bitcoin denominations jaganit? Uh nothing is fixed. So program can make any kind of denomination. So it's not having any fixed amount. If the double spending concept would not be there then a person with one bitcoin would be able to carry out infinite transaction. Correct answer. Correct. So once we start the transaction then our wallet freeze bitcoin which are used for transaction. Uh correct V. Okay. UTXO is received after confirmation of block. Why cannot it happen immediately at exchange. Sanjie it see in the transaction we are just waiting for the same purpose only and we are not making the block transaction wise. We are making the block as a collection of the transaction. So my block is not carrying one transaction it is carrying multiple transaction and we are talking about the distributed ledger. So whatever we do have this is into into we can say that this is into collectively with every every node. Okay. uh like let's say if she uh like let's say he she made a transaction of one bitcoin but as the double spending concept is not there so he will be able to transact that one bitcoin again because it is not deducted from his wallet see these scripts are what these are actually governing that all kind of utx and everything so for every transaction automatically programming is there which is being managed or which is managing that how uh the transfer will happen how the transaction will happen, how the UTXO will will be converted. So, automatically is embedded over there. So, as a user, you do not need to do anything for you. It is a normal graphical user interface. You just put your amount, click on send, uh put your uh sender address and everything. But by default, this is attached to the transaction and this is taking care of everything. Uh witness is something here we divide it. See this is we can say that public key script witnesses the balance of that script. So you can say that this is hash of all the transaction that has happened. So you can more consider it as a hash value for the uh the script that is being executed over there. So there is one more concept Rajes that is segated witness seg. So I'll explain that that time you'll get more understanding of this. So to understand this we'll cover segwit. So segwit is actually related to uh we can say data compression. So I'll explain this as well. Earlier it will it was not there but now the bitcoin has revised their uh scripts and they're including here witness and this is part of segwit which is more related to the data compression technique. But I'll explain this because because before understanding this segment we need to understand one more concept. Uh who is considered to be sender of UTXO amount. So this ashwan in this case the sender will be the transaction. Sender will be the transaction. So actually you know it recently happened not recently I'll say last year. Now we are into 2025. If I show you that that amount was you know very very high at that time see uh so we are talking about 21st July they have given the explanation and we can see how much of the asset so this is news of Hindu you see vazer crypto exchange hack how much of the asset was lost and what happened next so lost over 230 million in a security exploit 230 million is a very very big amount after one of its wallet was targeted on 18th July and has decided to socialize its losses in what uh unorthodox damage. So why I'm talking about this? So since beginning we have seen that blockchain came into the picture because of the security and transparent transparency we say that we we will not have any any kind of hacking or anything but this is also possible here so now one of the attack if I say do you think there is a possibility of the 51% attack on the bitcoin do you think there is a possibility of 51% attack logically you tell me is it possible or not logically probability is always there correct probability is always there so now what is 51% attack so we say that when a minor propose a block that has to be evaluated by the rest of the miners but now I'm saying that my 51% nodes into the system are corrupted so can I say that my entire blockchain is a failure in that case. Can I say that my entire blockchain is a failure in in that case? Can I say that? So yes. Yes. But if we see uh theoretically it is possible, theoretically it is possible but when we see that if somebody is actually trying to do that they need a lot more resources especially with the Ethereum. Especially with the Ethereum you see they need to buy all the ethers and everything. So uh in this case this becomes very difficult but this is also one of the attack and it might be possible somebody is taking over that that blockchain as well. So this is one of the type of attack. Another case I say here another case I say here mining pool. Do we all remember? Do we all remember what is mining pool? Mining pool. Can I say that? Group of miners working together. Can I say group of miners working together? So in that case you see group of miners they working together. Now let's say uh I I speak about that. So there was a time when China was the was having the highest mining pool. There was a time because now recently China has you know uh uh made it illegal to do the mining into their country. So now this this all mining pools has been shifted from China to the US. So now in this case you see geographically geographically can I say that we know the location of miners. Can I say that geographically we know the location of minors? Obviously I do not know the exact location but any any how we have a certain idea said that these miners are linked to one particular country one particular country. So what I'm trying to say here from majorly miners were running through China but now this has been shifted to US. Okay. Now is there any possibility? So one we are just you know probabilities we are considering is there any possibility that internet or the ISP working into the US that can be hacked probability you tell me internet service provider we understand ISP of US can that that be hacked is there any possibility probability yes probability is there but if you see US is having a very good security in terms of cyber security into the information security. So if we technically we talk about it is very difficult theoretically we say it is possible uh Jaganut ISP is internet service provider internet service provider so like we have the Tata and Jio here so which is which is providing us the internet services. So these are the ISP. So in this case you see we're talking about the throughout connection which which could be possible. So let me just give you more examples for this. Uh one of the attack is fishing attack. So fishing attack is what? Fishing attack is what? Have you received some kind of u lottery message? Have you received some kind of let's say uh your loan has been processed? you click on this link to get the further information. So all of us we receive this kind of you know messages. Similarly emails are also there. Emails are also there and uh even you might have received uh today what is what is going on. You receive a call from a couer kind of a guy and uh he will mention that you would your couer is there and if you need to return this or something you need to press that and uh do this. So these kind of things we see very normally. So what is fishing? Fishing is basically sending unauthorized links to someone. So that when they click on it actually your amount or you will get the financial loss. So in this case you see sometimes what happened let's say I do have uh I take example Exodus. Exodus comes in which category of wallet? Exodus comes in which category of wallet? Web, mobile or software? Which category? Which category? Both. Correct. That is that is also right. So this uh I assume that this I do have with the web based wallet or I do have some kind of mobile application. Now somebody sent me what? A link. a link on the same or I can say that a unauthorized link. So this is onto my WhatsApp and because of this unauthorized link what happened over there I actually clicked on that link and now this is making a automatic payment. This is making a payment from my mobile wallet to that account. So this is you see this could be done with the fishing site. This could be done with the fishing site. So there is a possibility that I have all these kind of a wallets and somebody is trying to intercept me. They will be sending me unauthorized link. If I click on the same link I will be thinking that there is nothing is happening but on the background my applications is being used and the amount is being transferred. So uh now another question if from my account I saw that uh some cryptocurrency is being transferred to a wrong address. Some cryptocurrency is being transferred to a wrong address. So can I get it back? Can I get it back? Can I complain it to someone? Is there any possibility like that? Something wrong happened. I by my mistake or by fishing there is a address where the transaction has been done. So can I get back that money? No, you cannot get back that money. So that is entirely not possible into the cryptocurrency system and even we do not have any any kind of you know uh compli uh regulatory framework as well where we can complain or something in our uh I'll say let's say in India we have the RBI to complain over there even if you see when you have some ATM card or something it has been lost so you can complain and you can immediately you know shut it down. These possibilities are there but nothing exists with the case of what the cryptocurrency. So that is why fishing is a very dangerous one into the case of Bitcoin. Okay. Now you see uh there is a civil attack also. This is very interesting one. This is very interesting one. So the cy attack listen this very carefully. So we all know the 51% logic. Do we all know the 51% logic? Now I am giving two statements. Correct me or give me your understanding onto this. So I'm giving two logic. One the one logic is that if my notes are honest 51% will be achieved soon. If my nodes are dishonest, 51% can be achieved with some delay. With some delay, think about it and then let me know. Two logics I have given. One, if my notes are honest, honest means whatever is the right or wrong, they are taking the decision and accordingly giving the verification. Let's say uh these nodes are having a proposed block. So what is what do I mean by the honest and dishonest node? So this is let's say this is a honest node. So this honest node will be giving the right decision. So if the proposed block is correct so it will be taking as correct. Dishonest node will be giving a wrong decision. Wrong decision is what? So in this case this node already computed that proposed block is correct but still it is saying it incorrect. Okay. So in this case now you read the read the statement. Now you read the statements. So now what is happening with this cyble attack symbol attack is we can say that a smaller version of 51%. A very smaller version. So now let's say there is a Bitcoin community and they have a competitor. The competitor is let's say XY Z. Now they want to they want to run their business and they want to disturb the Bitcoin's business. So what they did they created a civil attack. So civil attack is having dishonest nodes into the system. So they are not becoming minor for their reason. What they are becoming minor whenever they have come across the proposed block they will be voting as wrong way. They will be root vote voting into the wrong way only. So when they are doing it so ultimately they are getting delay to achieve the 51% attack. So in that case what will happen this 51% attack let's say it has to be achieved at 1010 now it might be go to the 1030 so I'm just taking a example for this or maybe 1020 so they are causing delay into the transaction or we can say the block confirmation uh no this is not to steal the bitcoin this is just to delay the see if the uh now you see if we have the average time of block confirmation of 10 minutes. We are still okay with that. But if it if it increases to 1 hour. So can we say that can we say that trading market will hit cryptocurrency trading market will hit. If that time becomes 1 hour it will obviously it will be it will be a hit. So there is a possibility that the other competitors they're not trying to steal anything. They're just having what? They're just having some malicious node into the system. These nodes just trying to disturb the working of other nodes. So that is the case of civil attack. So civil attack if I just brief it, this is creation of dishonest node into the system and these dishonest node will be doing the task into the wrong manner. But anyhow they cannot take the wrong decision because to take the wrong decision all the dishonest node should be 51%. And that is very high to achieve. So they cannot achieve it and smaller what they can do they can do the civil attack. How they achieve it to delay block confirmation. Correct? Uh when you think of I have a network let's say I try to dry draw it into paint. See, so let's say this is minor. This minor has already win the game and he is broadcasting the network network with the proposed block. This is one. This is one. This is one. This is one. This is one. This is so these all are nodes here. So I'm not taking 100 nodes now. I'm taking just few nodes. Now you see in this case let's say how we are moving geographically. It is getting the proposed block. It is sent to this. So this is also dishonest. It is sent to this dishonest. This is also dishonest. This is also dishonest. So in case it was not dishonest in case it was not dishonest. So by this time by this time it might have achieved the 51% thing. By this time it might have reach achieved the 51 percentile but now it has to wait to go through this also go through this also go through this also and only in the end ultimately it is having what it is having the right answer. So as of now you see the if we at this time if we see the quantity will remain same only quantity will remain same means the voting is 50% or whatever voting I'm talking about. So correct and incorrect voting that is entirely similar. So that is why we had having to say that delay is introduced here. One more case you see that broadcasting is happening and it will take time to reach from pier A2 or pier 1 to pier 10 in between whatever peer I am receiving that are dishonest. So as of now I cannot make any decision by that time because ultimately what we want we want 51%. So we are still waiting to get the confirmation from others right uh Vinnie I hope you understood this okay so I just delete this. So now we have seen the civil attack as well. uh fishing you already understood. See in the fishing how many things could be used? So chat fishing, message fishing, email fishing, social media fishing, Google Adword fishing. So all those could be medium for this. What is message fishing? What is mass message fishing? Can I say my text message? The medium is my text message. the which we are receiving on the phone email we all understand social media so now you see on the Instagram also we are getting you know these kind of messages so Google adword is also one of the example so yes we do have multiple links sent through the message correct correct so normal text message when it is coming through the email this is this is your uh the links are coming to from the email over okay now I come to the rooting ing attacks. So now what is the rooting attack? So this is basically targeted to the no now you see this is not being targeted to a user or something. This is onto the network. Now in the network you see this is what BGP router. Now BGP stands for border gateway protocol. This stands for border gateway protocol. And now in this case you see we are actually having uh when I'll just come to this border gateway protocol. Now in this case you see this is based on what this is trying to give the directions to the packet. So when it is trying to give the directions to the packet let's say this is being hacked. Can I say that packet will be going to a wrong direction? Packet will be going to a wrong direction. Can I say that if this particular router is being hacked, that router's responsibility was just to give the direction like where it should transfer to the next. Now this is doing a wrong task. So in this case you see this is also one of the type of attack where rather than targeting a particular scenario the router or these kind of a devices are being hacked by the hackers and this this can be maliciously maliciously send this packet to some other location so this is not only with the blockchain this could happen with any type of data this is not only with the blockchain okay uh V I'm coming to your question once validator validates block then only He send it to peer node to validate it. Uh correct Vinnie. So maybe you wanted to say minor validates the block then only he sent it to the peer node to validate it. So it is just like a proposed block. So all other miners need to revalidate it to get the 51% voting. Okay. Uh this also I I believe we have already discussed what is full node to become minor. What you need to become full node or light node? To become minor? What you need to become? Full node or minor? Full node. Full node. Full node is downloading the entire blockchain. Uh Rajes, this PPT is available on your uh portal, but I'll show you where it is available. Okay. Full node. Full node. Okay. What what is light node? Who is light node then? Who is light node? Viewers. So can I say that if I am on the uh blockchain explorer, I am I am working as uh light node. I'm on the blockchain explorer and can I say that I am a light node? So yes, I'm on the light node. Now you see uh one more thing we see here. Let's say I want to join the network. I want to become the miner. What I want to become? I want to become full node. So full node. So we have seen a website. We'll visit the uh bitcoin website. What we will do? We will download the bitcoin software. Now when we are downloading the Bitcoin software, the server will be connecting me to a node. The server will be connecting to me a node. Now you see I requested a C node. C node is providing me all the addresses. See now what are the address we talked about that this is tier to tier network. So I should have if I am becoming a minor I should have addresses of all other peers. I should have addresses of all other peers. Okay. So but who will be providing me all those addresses? How I will be connected? I'm saying that I want to become a part of peer-to-peer network. So we will when I'm downloading the bitcoin I will be linked to a seed node. So seed node will be providing me address list of all the peers so that I can form a connection with those peers as well. So every time a new node or a new minor joins the network the same process happens. So requesting the C node, retrieving the address list, selecting the peer node and updating updating the network. Now why I'm saying updated the updating the network. So let's say I have 101 peers. Now one more is added. So there is one more connection. So 101 + 1 that is equal to 102 peers. Now can I say that recent peer will be also added also added in the also added in the address list. Can I say that recent peer will be also added in the list. Can I say that? Yes, it has to be added because it is just what address list over there. Ash I'll come to your question just give me a second. Uh now in this case you see the same process we are following up here. So seed node connected with this node give me the address list by this address list it is getting connected to all other list as well. So this is making a updated copy into the network mining we all understand. Now let me come to the Ashwin's question. uh when a block when then when then a block is broadcasted to a node does it forward to another node only after it has completed completed validating the node no Ashwin it is into the process so let's say I received a block I'm working on that and meanwhile it is being transferred to others as well because for my verification also it takes time so it is not wasting into that broadcasting is sending to everyone So what whatever I have I'll update with my answer correct or incorrect so that I'll update to the bitcoin. Okay. Now we'll come to the orphan block. This is also left. Do we have facility to select our peer nodes? uh when it is automatically selected but if you need to select the immediate peer that you can you can select the immediate pier. So one term is immediate pier. Immediate peer is that is closest to your your connection. So that you can choose but uh see you will not be knowing the exact thing over there. Everything is encrypted. So you're not knowing IP address or something. You're know not knowing that okay this person is belong to which city or which country but it is showing you the nearby route. Every information is encrypted. Okay, next concept is orphan block. Uh, can I move to this? Next concept is orphan block. Can I move to this? Okay, now you see now you see in this case uh this is the concept which we left when we started with the proof of work. The question was what if more than one minor solves the puzzle at same time. Okay. So one case we asked is it possible? So the answer is yes it is possible. So what will happen in that case? So initially it is very difficult for bitcoin to recognize this. So what happened into that case? Now you think of a case that I have minor A and minor B. So these miners solved the puzzle. Let's say uh nons. He also received the nons. He also got the nons. So both of them created their block. So they started. They are not aware about the things here. The broadcasting has been started. What is broadcasting? What is broadcasting? Now, now you should understand this. What is broadcasting? Can I say that? Sending the proposed block to the multiple one. Can I say that sending the proposed block to the multiple peers forwarding to another node? Yes. So, broadcasting is what? Uh, let me write it here as well. So, for your later understanding. So I'm writing here broadcasting is broadcasting is sending proposed block to all peers. Okay. Block to all peers. All right. Now this is also doing the broadcasting. This is also doing the broadcasting. Now there is problem. Now how many miners are doing it? two minors currently if you see you can add you can work on only adding up one block. So there is a function we can say or a programmically with the help of program there is a function call we say function call that is known as synchronization call we call it sync call. So that happens in the blockchain with all the peers and what it checks it checks the it checks the all blockchain peers or all peers all peers are having the same state of the blockchain or not. Peers having the same state of blockchain or not. Okay. So when it is recognizing so it got what it got let's say minor A is adding block X minor B is adding block Y. Now in this case they found out they find out the sync call the sync call that is a program that find out that block block x block x which is related to minor 8 block x is having introduced into 50 peers. block Y is there into 30 pairs. Okay. So now you see two different blocks are being floated into the blockchain. One is block X, one is block Y, block X is through minor A, block Y is through minor B. Reason was there that they solved the nons at the same time. But it has been recognized with the sync call only. So sync call is being done after a fixed amount of time. Okay, now you see they need to choose one. Which one is easy to delete or which one is easy to discard? What should I discard? 50 pier or 30 pier? What should I discard? 50 pier or 30 pier? Which is better to discard? Which is better to discard? 30 pier. 30 pier. So now which block is this one? Which block is this one? Block Y. Block Y is associated to which minor? minor B. So I say here block Y while will be discarded by the synchronization call and this is known as orphan block now. Okay. So now you see this is being discarded. So these all 30 tiers will be also updated by block X whenever the time comes. Meanwhile, all those transactions which were part of orphan black block, listen this carefully. Let's say I have total 1,000 transactions that were part of orphan block. Now they all will be transferred to the unconfirmed transaction pool. they all will be transferred to the unconfirmed transaction pool. So now you see in this case what is happening in this case this example you see can you see here block 3 A and block 3B can you see here block 3 A and 3B. So this is being discarded and it is known as orphan block. So this being sent to back to the unconfirmed transaction so that the same state remain with the blockchain. Okay. I hope now you understand this concept. What is the orphan block? So what will be your answer? If you you want to give in two lines, what is orphan block? What is orphan block? But how you can define this discarded block? Yes, discarded block. Correct. So in case you see if uh three miners are doing at the same time so same thing happen will that only one will be chosen as the final block. Correct. Uh now proof of stake is having the pro orphan block or not. Proof of stake is having the orphan block or not? No they are not having. It is not having. And also let me tell you one thing uh earlier Ethereum was Ethereum 1.2 1.0 Ethereum 1.0 was using proof of work. That time orphan block was known as uncle block in the Ethereum. See in the bitcoin the name is always same in