Building a Blockchain in Under 15 Minutes - Programmer explains

Building a Blockchain in Under 15 Minutes - Programmer explains
I wanted to demonstrate that the concept of a blockchain that powers almost all of the modern cryptocurrencies is very simple at its core. 

Bitcoin, Ethereum, Litecoin etc all are based on this blockchain technology. Many people think that the blockchain is a complicated thing while at it's core its just a clever use case of hashes.

Enjoy guys!

CODE: https://github.com/ivan-liljeqvist/SimpleBlockchain


Hardware wallets:
♥ TREZOR https://trezor.io
♥ LEDGER NANO S https://www.ledgerwallet.com/r/4607

To buy cryptocurrencies:
♥ Coinbase https://www.coinbase.com/join/529bab0ab08ded7080000019



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  • Tony Fallows
    has me stuff
  • Dot Rule
    Total outsider with no tech knowledge but I understood what you were saying.
    Thanks, Ivan. Great job explaining.
    Btw, is there a more elaborate video for total newbies like me to learn more on how to use the program and such ?
  • prudhvi j
    How to become a blockchain developer.
    .without programming knowledge...pls tell me how to start where to start...step by step plese
  • Alexsey Orlov
    nice video, but where digital signature and where consensus algorithms ?
  • Csaba Toth
    "This kind of hash is very hard to crack" - wrong. The example could very well use MD5 or even better: SHA256. Very easy to use with Java. You could claim that it's very hard to crack then. The regular Java class's hash function is not a cryptographic hash function in the sense that it'd be hard to crack.
  • Sohail ali farooqui
    Great video for understanding the concept and implementation of hashing. I am trying to build a decentralized blockchain application for tracking charitable donations made by people from their bank accounts, any leads or tool which can help me out regarding this anyone ? I am well versed in java, javascript, html, css, C#, mySQL. Any help or pointing in right direction will be much appreciated.
  • Dr Williams
    I think I get it.. it's a bit like CRC error correction.. where it sends the end and the beginning tags of the packet "block" to make sure the ther side has received the same data. It's a receipt! That it ??
  • Santosh Nandur
    Can we use block chain technology in voting ? explain how it can be done
  • DSAS
    ok, so does a new blockchain figure a fork in an existing blockchain? and does that mean it´s more secure or easier to secure?
  • musa nuhu
    well Ivan I have been impressed
  • Vishnu Agrawal
    Excellent Ivan. Good job
  • Mozzthecoolguy
    Ivan, super stuff you made! Thanks a million!
  • Osh Bazar
    Can we create blockchain without Money or Economics? I wish to create a private personal blockchain only to store data. Will it be easy like this? I don't want block + chain. I want a single block that stores any information. And if it is private blockchain Can I delete, add, update data?
  • AB Softech
    how to upload blockchain in an crypto exchange, We made in JAVA
  • p473r
    how is this guy calling himself a programmer? "A hash is a digital signature"? seriously? He's using Java hashCode() for blocks??
    i mean you can just google these concepts in 2 minutes and find that most of what he's saying is completely wrong
  • Goutham Sivakumar
    What are the software or platform needed for blockchain using java code?
  • sal joe
    Excellent presentation; this gave me a good idea of how blockchain is implemented.
  • Morgan Warren
    Thank you, it was very interesting and affordable!
  • Bitcoin Cash
    This Kid needs a slap, lying to and scaming youtube subscribers and to the crypto community!
  • 张梓径
    Very misleading
  • DanHughes
    great job
  • Yovo Manolov
    This video is a killer ! Thank you very much. Very well explained!
  • Sola Han
    What if you lie right after the block is formed?
  • picostan
    Blockchain concept is "Simple yet profound!"
  • jacob nehama
    seared for python not java
  • E. tX
    HI IVAN, how to token 100 poems with a blockchain or holochain, to guarantee "authenticity" over them, could you develop it? thanks
  • 이용기
    Thanks!! your video is awesome
  • Cody Gonzalez
    Thank you, brother, I put my finger up! You really met in 15 minutes and everything was clearly explained!
  • julio A murillo
    DM on Instagram @seansoftengineer for software development, coding, programming, and app building. Tested and trusted, bet me he is pro
  • Ernie QT
  • Danilo
    could make a sales web wallet with its own node to handle private public keys please
  • parmila kargar
    Plzz kindly upload the soft copy of this software u write code on it.
  • parmila kargar
    On which program u wrote this code may I know?
  • hareram sharma
    nice video. could you please advice me how can shape up my career in blockchain as i am java developer
  • saimondal
    Well described with in 15 mins. do you have any other videos for Blockchain concept?
  • Carla Silva
    Hello, my friend, I'm Brazilian, I needed your help here in Brazil
    can you give the explanation of how the transaction will store in blockchain database, how to achieve the databse concepts(CRUD)
  • Yogesh Waichal
    Incredible video sir!
  • Shaun T
    great video
  • ms.marie
    Easy to understand. Thank you
  • asad polkoli
    You left me with a smile .
  • Vedran Janjetovic
    Hash is not equal to digital signature...Hash is something like imprint or 'fingerprint'.
  • Kevin McKee
    Java I do one in JavaScript and my hash I had to import so this will be fun.
  • Tom Takumi Okamoto
    How do you authenticate a transaction in a blockchain?
  • mineralt
    Great video...thank you
  • Artyom Khateev
    Спасибо. Просто и доступно)
    Great explanation. Thanks.
    Of course, I'm left with the basic Q's. Maybe you can have a shot at some.

    1) So where are the repositories for all these blocks? If this was an RDB or a web server, someone would be hosting it. Who is hosting the block repositories? And who makes block repositories software? I see Oracle are launching a blockchain platform soon.

    2) How many copies are there? Who regulates how many copies? In a RDB world this might be called replication or shadow copies.

    3) Who decides which copy is the truth, if say there's only 2 copies and they're in contention?

    The low level stuff is of course loved by geeks. The high level infrastructure though in which the cool code lives is just a important.
  • MindSet trading
    How suppose to check&confirm the transactions between the blocks ?
  • uzu J
    ""Digital signiture""..
  • Prem Kumar
    I mearly scratched the surface ......great video though ...thanks ivan.