Bitcoin For Dummies. Peter Kent

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СКАЧАТЬ it’s used to sign messages that you send to the blockchain. These messages are the ones that trigger transactions and updates to the blockchain ledger. We’ll explain this signing process in a moment, but to understand that, you have to understand a little about the magical keys.

      Public key encryption magic

      Public key encryption is a clever little trick created using digital cryptography. This type of encryption is all accomplished using hugely complicated mathematics — the sort of mathematics that even most people with advanced degrees in mathematics don’t understand, the sort of mathematics that has names like Carmichael numbers and Goppa codes, the sort of mathematics that we certainly don’t understand, and you don’t either (well, most of you, dear readers, don’t). But that’s fine; gravity isn’t well understood either, but we all use it every day. So, forget how this amazing stuff works, and consider instead what it is actually accomplishing. Peter likes to call this mathemagics; sure, it’s mathematics, but it’s amazing and almost nobody understands it, so it might as well be magic! Here’s how it works.

      First, imagine a safe, with two keyholes and two associated keys. We’ll call one the public key, and one the private key. Now imagine that you put something into the safe and lock it using the public key. Once the door is closed and locked, the public key no longer has access to the safe; it can’t be used to unlock the safe and extract the item. The private key, however, will work. In fact, once the safe is locked, the only way to open it is to use the private key.

      That’s weird enough, but it gets even stranger. This magical mathematical safe actually works both ways. You can also lock it with the private key, but after you lock it, you can’t use the private key to open the safe. Only the public key will open a safe locked with a private key.

Oh, and these two keys are magically associated. They work only with each other and no other keys. Private Key X will work only with Public Key X, and vice versa. You can’t lock the safe with Public Key X and then unlock the safe with Private Key W or Private Key K, for example.

      Okay, same principle, but now think of electronic messages. You can lock an electronic message with a public key — that is, you can use a key to scramble, or encrypt, the message. That message may be an email or information being sent from your browser to a web server.

      After that locked (encrypted) message is received at the other end (by the email recipient or the web server), only the private key can unlock it; the public key is useless at this point. And again, the private key must be the mathemagically associated key (okay, mathematically associated), and no other.

      Encryption is a handy tool. It means Peter can give you a public key, and you can write him a message and encrypt it using the public key; once it is encrypted, nobody in the world can read it unless they have the private key. So, if Peter carefully protects his keys, he’s the only person in the world who can read it.

      The names of these keys aren’t arbitrary. The private key should be truly private — only you, and nobody else in the world, should have access to it. The public key can be truly public. You can give it away. For example, if you want to have people email encrypted messages to you, you could publish your public key — on your website, in the footer of your emails, on your business card, or whatever — so that anybody who wants to send a message to you can encrypt it with your public key knowing that you are the only person in the world who can read it (because you keep the private key secret).

      This process is essentially what your web browser uses when you send your credit card information online; the web browser uses the web server’s public key to scramble the data so that only the web browser, with the associated private key, can decrypt and read the credit card information. (Okay, that’s a simplification. Browser-to-server communication is more complicated than this description, involving temporary session keys and so on; but the basic principle still applies.)

      HOW DO YOU ENCRYPT EMAILS?

      Email encryption has been around for decades, but it simply never caught on with the public at large. Still, you can encrypt email from most email systems, such as Outlook, Gmail, and Yahoo! Mail, and systems, such as ProtonMail, can encrypt it by default. If you’re interested, you can dig deep into the Help pages.

      Messages to the blockchain

      That’s public key encryption, then. But if the blockchain is not encrypted, what does it have to do with Bitcoin? Well, you use public-key encryption when you send transactions to the blockchain. When you want to send Bitcoin to someone else, you send an encrypted message to the blockchain saying, “Send x.xx of my Bitcoin to this address.”

      But wait. We just told you the blockchain isn’t encrypted, and now we’re telling you a message to the blockchain is encrypted! So why do you care if the message going to the blockchain is encrypted if you’re just going to decrypt it anyway?

      Well, remember that we told you this lock-and-unlock mechanism works both ways. You can lock with the public key and unlock with the private key or lock with the private key and unlock with the public key. Either way, the data is scrambled. The difference is in who has the ability to unscramble it. If you scramble something with the public key, the only person in the world who can unscramble it is the person with the private key. But if you scramble it with the private key, the only person in the world who can open it is…everybody! Anybody and everybody can get to the public key. It’s public, remember!

      So, what’s the purpose of encrypting a message with the private key? Not to secure it, obviously, because anybody can decrypt it. No, the purpose is to sign the message (transaction) and prove ownership of the associated public key.

      Signing messages with the private key

      Let’s go back to the concept of encrypted email for a moment, to help you understand. Let’s say that Peter publishes his public key on his website, in his emails, and on his business cards. Now, one day you get a message that seems to come from Peter. But how can you be sure it’s from him? Well, he encrypted the message using his private key. So, you take his public key (which is publicly available) and use it to decrypt the message. If the message really is from Peter, his public key will decrypt it, and you’ll be able to read it. If it isn’t, the decryption won’t work, because it came from someone else.

      So, by encrypting the message with the private key, Peter has in effect signed the message, proving that it came from him. The recipient knows that the message was created by the person holding the private key that is associated with the public key that opened the message up and made it readable.

      Okay, back to Bitcoin. Remember that these three things are mathemagically associated with each other. Your address in the blockchain was created by your wallet software, which has a private key that was used to create a public key, and which then used the public key to create an address. All done with the magic of mathematics.

      Thus, the private key is associated, through the public key, with the address. Remember also that these elements are all unique and operate with each other. The address is associated with just one private key and one public key, each of which are uniquely associated with each other.

      Sending a transaction message to the Bitcoin ledger

So, here’s how cryptography is used when you want to send a transaction to the blockchain, СКАЧАТЬ