3. Blockchain Basics & Cryptography

MIT 15.S12 Blockchain and Money, Fall 2018
Instructor: Prof. Gary Gensler
View the complete course: https://ocw.mit.edu/15-S12F18
YouTube Playlist: https://www.youtube.com/playlist?list=PLUl4u3cNGP63UUkfL0onkxF6MYgVa04Fn

In this lecture, Prof. Gensler, explains the basics of blockchain and covers Bitcoin design features, hash functions, blocker headers, Merkle trees, among other related topics.

License: Creative Commons BY-NC-SA
More information at https://ocw.mit.edu/terms
More courses at https://ocw.mit.edu

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About the Author: Jose Alarcon


  1. I dont understand why no one asked why proof of work is necessary? Cant any other usefull system can be implemented. He talks about solving puzzle but no one asked what is the puzzle in detail and why is there a puzzle? Solving hash functions and nonces accordingly is ofcourse but they did not question the methodology of the work.

  2. Wow I could be in MIT. I did more readings then them 😀 and understood all. Great professor and it made me confident with myself. Thanks MIT, send me free stuff :DDD

  3. Question: If there are 10 to the 8 Satoshis per bitcoin, is that why that is the granularity of a bitcoin? That is, I have heard that you can break up a bitcoin into one out of a hundred million. Or, 10 to the 8th.

  4. Where can I find the Bosworth blockchain demo?

    Prof/Chairman Gensler refers to the demo app constructed by Andreas Bosworth. A link is presented in the introduction that links to a website that is now “owned” by someone other than Bosworth.

    Please point me to the actual demo app, not the video. Thanks

  5. 42:00 With the digibyte blockchain, you can download the entire blockchain quite easily. The exact mechanics Im not sure but its must more faster, scalable, and decentralized than any blockchain currently available.

  6. this lecture had been told to me to learn by my university as blockchain is my self paced course .It was really good lecture even though i was lacking on so many points in lecture i found it very interesting to eatch and not drop on some point i dont get.so i think he is one of the best teachers i had ever been taught ..hats off sir

  7. can someone pleas explain to me how to generate private and public keys safely? I don't understand. If even the big hedge funds don't do it correctly then i forsure don’t. 57:00

  8. diffie hellman did pretty good privacy for email before bit coin think of the trap door hash function example add 2 primes even if u have the total u cannot recover the primes one is the public key one is the private key u need both to have validation. basically it is the one way trapdoor.

  9. A digital signature is used to secure the Non-repudiation of a message or transaction. This simply means that it should be possible to establish if this message or transaction was indeed created and by whom. You should also not be able to say you didn't create the message if you indeed did create it.

    It does not encrypt the message FULL STOP.

    Example: If you send an email to someone and put your digital signature on the message. Anyone that could access the message could still read it, as it is not encrypted. They could also verify that you sent the message by verifying the digital signature.

    Think of a digital signature to be the equivalent of you signing a document with a pen. People who know your handwriting will be able to tell that you actually signed this document. That it was not falsely produced by some third party. You should also not be able to deny signing the contract.

    You don't want someone else to be able to sign a contract in your name, right?
    Nor do the one you entered the agreement with want you to be able to deny signing the contract.

    repudiated: to reject as unauthorized or as having no binding force – Merriam Webster

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