Alice has created her bitcoin wallet and she is now ready to receive funds. Her wallet
application randomly generated a private key (described in more detail in “Private
Keys” on page 63) together with its corresponding bitcoin address. At this point, her
bitcoin address is not known to the bitcoin network or “registered” with any part of the
bitcoin system. Her bitcoin address is simply a number that corresponds to a key that
she can use to control access to the funds. There is no account or association between
that address and an account. Until the moment this address is referenced as the recipient
of value in a transaction posted on the bitcoin ledger (the blockchain), it is simply part
of the vast number of possible addresses that are “valid” in bitcoin. Once it has been
associated with a transaction, it becomes part of the known addresses in the network
and Alice can check its balance on the public ledger.
Alice meets her friend Joe, who introduced her to bitcoin, at a local restaurant so they
can exchange some US dollars and put some bitcoins into her account. She has brought
a printout of her address and the QR code as displayed in her bitcoin wallet. There is
nothing sensitive, from a security perspective, about the bitcoin address. It can be posted
anywhere without risking the security of her account.
Alice wants to convert just 10 US dollars into bitcoin, so as not to risk too much money
on this new technology. She gives Joe a $10 bill and the printout of her address so that
Joe can send her the equivalent amount of bitcoin.
Next, Joe has to figure out the exchange rate so that he can give the correct amount of
bitcoin to Alice. There are hundreds of applications and websites that can provide the
current market rate. Here are some of the most popular:
Bitcoin Charts
A market data listing service that shows the market rate of bitcoin across many
exchanges around the globe, denominated in different local currencies
Bitcoin Average
A site that provides a simple view of the volume-weighted-average for each currency
ZeroBlock
A free Android and iOS application that can display a bitcoin price from different
exchanges (see Figure 1-3)
Bitcoin Wisdom
Another market data listing service
Using one of the applications or websites just listed, Joe determines the price of bitcoin
to be approximately 100 US dollars per bitcoin. At that rate he should give Alice 0.10
bitcoin, also known as 100 millibits, in return for the 10 US dollars she gave him.
Once Joe has established a fair exchange price, he opens his mobile wallet application
and selects to “send” bitcoin. For example, if using the Blockchain mobile wallet on an
Android phone, he would see a screen requesting two inputs, as shown in Figure 1-4.
• The destination bitcoin address for the transaction
• The amount of bitcoin to send
In the input field for the bitcoin address, there is a small icon that looks like a QR code.
This allows Joe to scan the barcode with his smartphone camera so that he doesn’t have
to type in Alice’s bitcoin address (1Cdid9KFAaatwczBwBttQcwXYCpvK8h7FK), which is
quite long and difficult to type. Joe taps the QR code icon and activates the smartphone
camera, scanning the QR code from Alice’s printed wallet that she brought with her.
The mobile wallet application fills in the bitcoin address and Joe can check that it scan‐
ned correctly by comparing a few digits from the address with the address printed by
Alice.
Joe then enters the bitcoin value for the transaction, 0.10 bitcoin. He carefully checks
to make sure he has entered the correct amount, because he is about to transmit money
and any mistake could be costly. Finally, he presses Send to transmit the transaction.
Joe’s mobile bitcoin wallet constructs a transaction that assigns 0.10 bitcoin to the address
provided by Alice, sourcing the funds from Joe’s wallet and signing the transaction
with Joe’s private keys. This tells the bitcoin network that Joe has authorized a transfer
of value from one of his addresses to Alice’s new address. As the transaction is transmitted
via the peer-to-peer protocol, it quickly propagates across the bitcoin network.
In less than a second, most of the well-connected nodes in the network receive the
transaction and see Alice’s address for the first time.
If Alice has a smartphone or laptop with her, she will also be able to see the transaction.
The bitcoin ledger—a constantly growing file that records every bitcoin transaction that
has ever occurred—is public, meaning that all she has to do is look up her own address
and see if any funds have been sent to it. She can do this quite easily at the blockchain.info
website by entering her address in the search box. The website will show her a page
listing all the transactions to and from that address. If Alice is watching that page, it will
update to show a new transaction transferring 0.10 bitcoin to her balance soon after Joe
hits Send.
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AJÁNLOM AZ OLDALT