1. JO
    Where to surf today

    The problem:

    Imagine you are in Portugal, you want to go surfing, but you don't know where the best waves are.

    What do you do?

    Well, you open your surf guide, see what surf spots are near enough, search for a beachcam on that spot, and after some thorough evaluation, you finally decide where to go. Now it's time to search for the spot on G…

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    04 Mar 2024

  2. JO
    License to steal

    Every now and then people ask me for iOS versions of my mobile apps.

    I don't build them, due to the following text in the Apple Developer Agreement:

    11. Apple Independent Development. Nothing in this Agreement will impair Apple’s right to develop, acquire, license, market, promote or distribute products, software or technologies that perform the…
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    04 Mar 2024

  3. JO
    Buy men’s underwear and help an athlete

    Today I'm proud to announce http://hatitude.pt, the place where you help an athlete every time you buy men's underwear. The idea was presented to me by Hugo. I loved it, and so I decided to help him by developing the website.

    The problem

    As you might know, only a couple of sports - like football - have financial help and support. There are thousa…

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    04 Mar 2024

  4. JO
    Analysis of Bitcoin Cash double spends

    Bitcoin Cash double spends

    Double spend is when a set of coins is spent in more than one transaction. This can happen for various reasons, but one of the reasons is fraud attempts.

    Bitcoin Cash accepts 0-conf payments, which I consider insecure by default. But I would like to have some data to support this, so I went looking.

    Since …

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    04 Mar 2024

  5. JO
    Explain Bitcoin like I’m 10

    How can I buy Bitcoin?
    Generate a password, and then pay someone to send bitcoins to that password.

    A password?! That's it?
    Yep, that's it.

    What do you mean with "send to a password"?
    It means those bitcoins now belong to the owner of that password.

    What if someone finds my password?
    Then he will be able to spend your bitcoins.


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    04 Mar 2024

  6. JO
    Maximum target hash

    Do you know which Bitcoin constant is this?


    Maybe in its hexadecimal format?


    Yes, it’s the maximum target hash.

    But what thus it means, and why this “weird” value?

    Bitcoin’s protocol wants b…

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    04 Mar 2024

  7. JO
    Explaining SIGHASH

    Sighash, short for Signature Hash, is a concept within the Bitcoin protocol that determines which parts of a transaction are signed. It plays a crucial role in ensuring the security and integrity of the Bitcoin network.

    By using different Sighash types, users have control over which parts of a transaction are mutable and which are immutable when …

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    04 Mar 2024