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  • If you've been sitting on the blockchain sidelines, it's time to catch up. Jonathan Waldman explores the core technical underpinnings on which many modern blockchain technologies are based.

    Read this article in the March 2018 issue of MSDN Magazine

    Thursday, March 1, 2018 7:29 PM
    Owner

All replies

  • Hi, Jonathan, very nice article that you have write.. i have one doubt..

    three paragraph above the figure 7, you wrote:
    "Bill is the owner of a digital asset and uses his private key to initiate a transfer of that digital asset to Susan. Susan’s transaction record uses Bill’s public key to verify his signature. After this, Susan’s public key is used to sign the digital asset, making Susan the new owner."

    Regarding the " Susan’s public key " the correct way would it be Susan use her Private Key??  so when Will Susan will use her Private Key in hash chain?

    Let me know your comments,

    with regards,

    Alexandre Oliveira


    Friday, March 9, 2018 5:04 PM
  • Hello Alexandre,

    Thank you again for contacting me. 

    I am revising my earlier response to you because the sentence you cited is misleading, as written. First, you are correct that Susan signs her digital asset using her private key. Second, signing doesn't make her the new owner--it makes the next person on the transaction chain the new owner. Susan's public key is involved, but what actually happens is that when Bill transfers his digital asset to Susan, he needs Susan's public key and Susan's public key is written to the transaction record that makes Susan the new owner. Thus, the published sentence should have been: "After this, Susan’s public key is used to create a new transaction record for the signed digital asset, making Susan the new owner."

    In my upcoming article, I will provide far more detail as to what happens on the blockchains like Bitcoin when digital assets are transferred from one owner to the next. 

    Thank you,
    Jonathan
    Friday, March 9, 2018 9:48 PM
  • Wow, this article looks intimidating from the outset, but it is excellently written and easy to understand.  Thank you for sharing your knowledge in such a digestible fashion!  I'm full now. :)

    Monday, March 12, 2018 12:04 PM
  • You're quite welcome, and thank you for your comments.

    Regards,
    Jonathan
    Monday, March 12, 2018 4:23 PM
  • Very clear article.

    I tested the double hash examples and I found that the hash values presented correspond to the hexadecimal string representations of the first ones, not the binary hash values themselves.

    Regards,

    Gabriel

    Wednesday, March 14, 2018 12:29 PM
  • Gabriel, thank you for your comments and observation.

    Indeed, the article states that if I double-hash "the hash values shown in Figure 1", I end up with the results in Figure 2. I did in fact pass each of the hexadecimal strings shown in Figure 1 through the SHA-256 algorithm in order to arrive at the respective double-hash values shown in Figure 2. I chose this method of using the 64-byte hexadecimal string value as input so that users could double-hash the Figure 1 values using the website I had cited in the article [onlinemd5.com], which accepts an ASCII string as input. 

    The method of double-hashing you're referring uses the 32-byte binary value (256 bits/8 = 32 bytes) produced by the first hash operation as input to the second. 

    The takeaway regarding double-hashing is that it guards against a length-extension attack (to which the SHA-256 algorithm is vulnerable) and can help thwart a casual pre-image attack. Because hash functions are one-way functions, it's not feasible to algorithmically reverse the double-hash value back to the single-hash value (especially if the second hash is constructed using a different hash algorithm)--making it infeasible to conduct a successful pre-image attack. In the context of the article, double-hashing using the 64-byte hexadecimal string value versus the 32-byte binary value achieves a similar cryptographic consequence which is primarily to guard against a length-extension attack. 

    Thursday, March 15, 2018 4:27 PM
  • I looked into crypto last year and I have to say this article is a superb refresher.  I'll recommend this article to anyone as a primer for block-chain.  Very well done.

    Yours

    Monday, March 19, 2018 5:00 PM
  • Meadensi, I appreciate that--thank you. 
    Monday, March 19, 2018 10:30 PM
  • Jonathan,

    Unfortunately this is as far as I got with the article too. I still don't get what you are trying to say. Susan uses her public key to sign the digital asset. Does that mean she encrypts the whole document or the hash? Is that before or after she makes changes to the document (this is what you refer to as a digital asset correct?). I understand that she can prove she is the owner by being able to decrypt the document with her private key but how will the next person decrypt it and read it? Totally confused as to what is going on. I've researched blockchains before and the explanations are either not in depth enough or way too deep. You're article is the first one that strikes a balance and I appreciate your time in putting it together. However I can't get past this paragraph either. Would you have a good resource that you can point me to get me over the hump? Thanks! 

    Thursday, March 29, 2018 2:27 PM
  • Génial, cet article (https://msdn.microsoft.com/fr-fr/magazine/mt845650) peut sembler impressionnant dès le départ, mais il est très bien écrit et facile à comprendre. Merci de partager votre savoir de manière si digeste ! 
    Monday, April 16, 2018 1:00 PM
  • Jonathan,

    I'm trying to understand/grasp the need for BlockChain better and hence the question.

    The below paragraph mentions events that happened in the past and reminds us of the perils of living in a digital world. But my question is, while I agree a lot went wrong with respect to the subprime debacle, how could have blockchain technology help avoid the regrettable events leading to the 2008 disaster?

    So, similarly, the Heartland Payment Systems breach could have been avoided with Blockchain - How?

    Thanks,

    grajee

    <<In 2008, the subprime debacle occurred, during which long-­established, powerful U.S. financial institutions and insurance companies declared or teetered on the brink of bankruptcy. Those circumstances called for immediate federal government intervention in order to avoid a domestic and possibly global financial meltdown. This important event left a populace leery of centralized banks and exposed the danger of having financial ledgers closed to public scrutiny. In March 2008, the Heartland Payment Systems data breach exposed more than 130 million credit card numbers, many of which were later used to make fraudulent purchases.>>

    Thursday, April 26, 2018 7:00 PM
  • Grajee,

    Blockchain technology is a big subject and I could only write so much due to space constraints. The focus of my article was to discuss how blockchains work.

    Having said that, you asked a good question. In general, Blockchain technologies will help prevent such events because they offer decentralized authority as well as ledgers that are open to public scrutiny. The subprime debacle occurred as a result of highly leveraged investments in risky assets; the Heartland breach occurred--but it was the criminal use of the stolen data that ultimately caused damage. Having a ledger open to public scrutiny could have exposed the magnitude and type of risky investments made by banks that effectively had centralized control over their investments/ledgers, contributing to those factors that led to the subprime debacle; being able to enforce proper ownership of assets and track transactions on a tamper-proof ledger could have hindered casual criminal activity that resulted from the Heartland data breach. 

    Clearly, Blockchain technologies can't turn dishonest people or corporations into forthright entities. But they can reduce the likelihood that centralized rogue interests are able to exert unilateral control over assets tracked on a ledger that can be cooked as needed; and through their use of modern cryptographic algorithms, they can help to ensure that the transfer of assets is initiated by the asset owner rather than by an impostor. 

    Regards,
    Jonathan 


    Thursday, April 26, 2018 9:35 PM
  • Jonathan I finally got back to this. I understand exactly what you mean now. I reread the article which helped too :) Why is Susan the one that authorizes that the document is tamper free? Wouldn't that be Ludwig's responsibility? Shouldn't Susan encrypt her hash with her private key and Ludwig use her public key to decrypt the hash and compare hashes on his side? That's how the chain starts after all, Bill encrypted the original data asset hash with his private key and had Susan verify the hashes. Maybe we are being too abstract with this example and therefore the example is losing it's relevancy? Anyway thank you very much for the article and the help. 
    Tuesday, May 8, 2018 2:17 PM
  • Hello Craig,

    I am revising my earlier response to you because upon further review, the published sentence you cited is misleading, as written. First, you are correct that Susan signs her digital asset using her private key. Second, signing doesn't make her the new owner--it makes the next person on the transaction chain the new owner. Susan's public key is involved, but what actually happens is that when Bill transfers his digital asset to Susan, he needs Susan's public key and Susan's public key is written to the transaction record that makes Susan the new owner. Thus, the published sentence should have been: "After this, Susan’s public key is used to create a new transaction record for the signed digital asset, making Susan the new owner."

    In my upcoming article, I will provide far more detail as to what happens on the blockchains like Bitcoin when digital assets are transferred from one owner to the next. 

    Thank you,
    Jonathan



    Monday, May 14, 2018 8:11 PM