Bitcoin is a form of digital currency, created and held electronically. No one controls it. Bitcoins aren’t printed, like dollars or euros – they’re produced by people, and increasingly businesses, running computers all around the world, using software that solves mathematical problems.
It’s the first example of a growing category of money known as cryptocurrency.
What makes it different from normal currencies?
Bitcoin can be used to buy things electronically. In that sense, it’s like conventional dollars, euros, or yen, which are also traded digitally.
However, bitcoin’s most important characteristic, and the thing that makes it different to conventional money, is that it is decentralized. No single institution controls the bitcoin network. This puts some people at ease, because it means that a large bank can’t control their money.
Who created it?
A software developer called Satoshi Nakamoto proposed bitcoin, which was an electronic payment system based on mathematical proof. The idea was to produce a currency independent of any central authority, transferable electronically, more or less instantly, with very low transaction fees.
Who prints it?
No one. This currency isn’t physically printed in the shadows by a central bank, unaccountable to the population, and making its own rules. Those banks can simply produce more money to cover the national debt, thus devaluing their currency.
Instead, bitcoin is created digitally, by a community of people that anyone can join. Bitcoins are ‘mined’, using computing power in a distributed network.
This network also processes transactions made with the virtual currency, effectively making bitcoin its own payment network.
So you can’t churn out unlimited bitcoins?
That’s right. The bitcoin protocol – the rules that make bitcoin work – say that only 21 million bitcoins can ever be created by miners. However, these coins can be divided into smaller parts (the smallest divisible amount is one hundred millionth of a bitcoin and is called a ‘Satoshi’, after the founder of bitcoin).
What is bitcoin based on?
Conventional currency has been based on gold or silver. Theoretically, you knew that if you handed over a dollar at the bank, you could get some gold back (although this didn’t actually work in practice). But bitcoin isn’t based on gold; it’s based on mathematics.
Around the world, people are using software programs that follow a mathematical formula to produce bitcoins. The mathematical formula is freely available, so that anyone can check it.
The software is also open source, meaning that anyone can look at it to make sure that it does what it is supposed to.
What are its characteristics?
Bitcoin has several important features that set it apart from government-backed currencies.
1. It's decentralized
The bitcoin network isn’t controlled by one central authority. Every machine that mines bitcoin and processes transactions makes up a part of the network, and the machines work together. That means that, in theory, one central authority can’t tinker with monetary policy and cause a meltdown – or simply decide to take people’s bitcoins away from them, as the Central European Bank decided to do in Cyprus in early 2013. And if some part of the network goes offline for some reason, the money keeps on flowing.
2. It's easy to set up
Conventional banks make you jump through hoops simply to open a bank account. Setting up merchant accounts for payment is another Kafkaesque task, beset by bureaucracy. However, you can set up a bitcoin address in seconds, no questions asked, and with no fees payable.
3. It's anonymous
Well, kind of. Users can hold multiple bitcoin addresses, and they aren’t linked to names, addresses, or other personally identifying information. However…
4. It's completely transparent
…bitcoin stores details of every single transaction that ever happened in the network in a huge version of a general ledger, called the blockchain. The blockchain tells all.
If you have a publicly used bitcoin address, anyone can tell how many bitcoins are stored at that address. They just don’t know that it’s yours.
There are measures that people can take to make their activities more opaque on the bitcoin network, though, such as not using the same bitcoin addresses consistently, and not transferring lots of bitcoin to a single address.
5. Transaction fees are miniscule
Your bank may charge you a £10 fee for international transfers. Bitcoin doesn’t.
6. It’s fast
You can send money anywhere and it will arrive minutes later, as soon as the bitcoin network processes the payment.
7. It’s non-repudiable
When your bitcoins are sent, there’s no getting them back, unless the recipient returns them to you. They’re gone forever.
So, bitcoin has a lot going for it, in theory. But how does it work, in practice? Read more to find out how bitcoins are mined, what happens when a bitcoin transaction occurs, and how the network keeps track of everything.
How to Store Your Bitcoins?
Bitcoin wallets store the private keys that you need to access a bitcoin address and spend your funds. They come in different forms, designed for different types of device. You can even use paper storage to avoid having them on a computer at all. Of course, it is very important to secure and back up your bitcoin wallet.
Bitcoins are a modern equivalent of cash and, every day, another merchant starts accepting them as payment. We know how they are generated and how a bitcoin transaction works, but how are they stored? We store fiat cash in a physical wallet, and bitcoin works in a similar way, except it's normally digital.
Well, to be absolutely accurate, you don't technically store bitcoins anywhere. What you store are the secure digital keys used to access your public bitcoin addresses and sign transactions. This information is stored in a bitcoin wallet.
Bitcoin wallets come in a variety of forms. There are five main types of wallet: desktop, mobile, web, paper and hardware. Here’s how they work.
Desktop wallets
If you have already installed the original bitcoin client (Bitcoin Core), then you are running a wallet, but may not even know it. In addition to relaying transactions on the network, this software also enables you to create a bitcoin address for sending and receiving the virtual currency, and to store the private key for it.
There are other desktop wallets too, all with different features. MultiBit runs on Windows, Mac OSX, and Linux. Hive is an OS X-based wallet with some unique features, including an app store that connects directly to bitcoin services.
Some desktop wallets are tailored for enhanced security: Armory falls into this category.
Others focus on anonymity: DarkWallet – uses a lightweight browser plug-in to provide services including coin ‘mixing’ in which users’ coins are exchanged for others’, to prevent people tracking them.
Mobile wallets
Desktop-based wallets are all very well, but they aren't very useful if you are out on the street, trying to pay for something in a physical store. This is where a mobile wallet comes in handy. Running as an app on your smartphone, the wallet can store the private keys for your bitcoin addresses, and enable you to pay for things directly with your phone.
In some cases, a bitcoin wallet will even take advantage of a smartphone’s near-field communication (NFC) feature, enabling you to tap the phone against a reader and pay with bitcoins without having to enter any information at all.
One common feature of mobile wallets is that they are not full bitcoin clients. A full bitcoin client has to download the entire bitcoin blockchain, which is always growing and is multiple gigabytes in size. That could get you into a heap of trouble with your mobile service provider, who will be only too happy to send you a hefty bill for downloading it over a cellular link. Many phones wouldn't be able to hold the blockchain in their memory, in any case.
Instead, these mobile clients are often designed with simplified payment verification (SPV) in mind. They download a very small subset of the blockchain, and rely on other, trusted nodes in the bitcoin network to ensure that they have the right information.
Examples of mobile wallets include the Android-based Bitcoin wallet, Mycelium, Xapo and Blockchain (which keeps your bitcoin keys encrypted on your phone, and backed up on a web-based server).
Apple is notoriously paranoid about bitcoin wallets. Coinbase had its mobile wallet app pulled from the app store altogether in November 2013, and this was followed in February 2014 by removal of Blockchain’s iOS app. However, in July 2014, bitcoin wallet apps began to reappear on the iOS store, and now all of the major bitcoin wallet providers have released new editions of their previous apps.
There are also other types of wallets that can be used on a mobile, such as the browser-based wallet CoinPunk is developing. Another unusual wallet is the Aegis Bitcoin Wallet, which supports Android smartwatches.
Online wallets
Web-based wallets store your private keys online, on a computer controlled by someone else and connected to the Internet. Several such online services are available, and some of them link to mobile and desktop wallets, replicating your addresses between different devices that you own.
One advantage of web-based wallets is that you can access them from anywhere, regardless of which device you are using. However, they also have one major disadvantage: unless implemented correctly, they can put the organisation running the website in charge of your private keys – essentially taking your bitcoins out of your control. That’s a scary thought, especially if you begin to accrue lots of bitcoins.
Coinbase, an integrated wallet/bitcoin exchange operates its online wallet worldwide. Users in the US and Europe can buy bitcoin through its exchange services.
Circle offers users worldwide the chance to store, send, receive and buy bitcoins. Currently only US citizens are able to link bank accounts to deposit funds, but credit and debit cards are also an option for users in other countries.
Blockchain also hosts a popular web-based wallet, and Strongcoin offers what it calls a hybrid wallet, which lets you encrypt your private address keys before sending them to its servers – encryption is carried out in the browser.
Xapo aims to provide the convenience of an simple bitcoin wallet with the added security of a cold-storage vault.
Hardware wallets
Hardware wallets are currently very limited in number. These are dedicated devices that can hold private keys electronically and facilitate payments.
Trezor hardware wallet
The Trezor hardware wallet is targeted at bitcoiners who wish to maintain a substantial stash of coins, but do not want to rely on third-party bitcoin storage services or impractical forms of cold storage. Read our Trezor hardware wallet review to find out more.
Ledger USB wallet
The compact Ledger USB Bitcoin Wallet uses smartcard security and is available for areasonable price. CoinDesk reviewed this wallet in December 2014.
KeepKey launched a hardware wallet in September 2015, which is priced at $239 a unit. The KeepKey wallet software was originally a fork of Trezor's code.
Mycelium, Cryptolabs and BitStash currently have a hardware wallets in development, but, as of September 2015 none of these had delivered finished products. Announced on February 4th 2014, is the Nymi sports wristband from Boinym, which can act as a bitcoin wallet and uses your heart rhythm as a security key.
Paper wallets
One of the most popular and cheapest options for keeping your bitcoins safe is something called a paper wallet. There are several sites offering paper bitcoin wallet services. They will generate a bitcoin address for you and create an image containing two QR codes: one is the public address that you can use to receive bitcoins; the other is the private key, which you can use to spend bitcoins stored at that address.
The benefit of a paper wallet that is made correctly is that the private keys are not stored digitally anywhere, and are therefore not subject to standard cyber-attacks or hardware failures.
Are bitcoin wallets safe?
It depends how you manage them. The private keys stored in your wallet are the only way to access the transaction data stored in a bitcoin address. If you lose them, you lose your bitcoins. So, they are only safe in so far as no one else can access them, and they don’t get lost.
Are bitcoin wallets anonymous?
On the one hand, bitcoin is entirely anonymous. On the other, it is completely transparent and trackable. Due to this fact, bitcoin is often cited as being pseudonymous.
This fact resulted in some companies emerging with the goal of controversially tracking suspect transactions to 'police' the blockchain. To counter this, ideas were developed in the bitcoin community to take anonymity further, such as merge avoidance, stealth addresses, and coin mixing.
The alpha version of Dark Wallet – a crowdfunded bitcoin wallet – went live in May 2014. Created by Amir Taaki and Cody Wilson, Dark Wallet was designed to provide new tools for financial privacy, including in-built coin mixing and stealth wallet addresses. At the time of writing, the developers are urging users to use the testnet with 'play money' to iron out bugs before risking significant amounts of bitcoin.
Wallets and services like Dark Wallet ultimately mean that using bitcoin can be as anonymous as you want it to be.
How can I secure my wallet?
There are several ways to make your bitcoin wallet more secure:
Encrypt it
One way to protect your wallet from prying eyes is to encrypt it with a strong password. This makes it difficult to access your wallet, but not impossible. If your computer is compromised by malware, thieves could log your keystrokes to find your password.
Back it up
If you have your private keys stored in one wallet, but you mislay that wallet or it gets corrupted, you will lose your keys. Backing up your wallet makes a copy of your private keys, but it's important to back up your whole wallet. Some addresses are used to store change from transactions, and may not be shown to you by default. Back up the whole wallet in several different places, and keep them safe from prying eyes.
Use multisig
The number of services which support multi-signature transactions is increasing. Multi-signature addresses allow multiple parties to partially seed an address with a public key. When someone wants to spend some of the bitcoins, they need some of these people to sign their transaction in addition to themselves. The required number of signatures is agreed at the start when people create the address.
Since multiple signatures are needed before funds can be spent, the additional signatures could come from, say, a business partner, your significant other, or even from a second device which you own, to add a second factor to spending your coins.
Take it offline
If you are too nervous to store your bitcoin keys digitally, for fear that they may be stolen by hackers, there is another option: ‘cold storage’. Cold storage wallets store private bitcoin keys offline, so that they can’t be stolen by someone else on the Internet.
It’s a good idea to use cold storage for the bulk of your bitcoin fortune, and transfer just a little to separate bitcoin addresses in a ‘hot’ wallet with an Internet connection, making it easy to spend. That way, even if your mobile phone is lost, or the hot wallet on your notebook PC is erased during a hard drive crash, only a small amount of bitcoin cash is at risk.
Many software bitcoin wallets feature a cold storage option. Or, you could go completely analogue, and simply use paper wallets for offline storage.
Paper wallet image via zcopley / Flickr
Balances - block chain
The block chain is a shared public ledger on which the entire Bitcoin network relies. All confirmed transactions are included in the block chain. This way, Bitcoin wallets can calculate their spendable balance and new transactions can be verified to be spending bitcoins that are actually owned by the spender. The integrity and the chronological order of the block chain are enforced with cryptography.
Transactions - private keys
A transaction is a transfer of value between Bitcoin wallets that gets included in the block chain. Bitcoin wallets keep a secret piece of data called a private key or seed, which is used to sign transactions, providing a mathematical proof that they have come from the owner of the wallet. The signature also prevents the transaction from being altered by anybody once it has been issued. All transactions are broadcast between users and usually begin to be confirmed by the network in the following 10 minutes, through a process called mining.
Processing - mining
Mining is a distributed consensus system that is used to confirm waiting transactions by including them in the block chain. It enforces a chronological order in the block chain, protects the neutrality of the network, and allows different computers to agree on the state of the system. To be confirmed, transactions must be packed in a block that fits very strict cryptographic rules that will be verified by the network. These rules prevent previous blocks from being modified because doing so would invalidate all following blocks. Mining also creates the equivalent of a competitive lottery that prevents any individual from easily adding new blocks consecutively in the block chain. This way, no individuals can control what is included in the block chain or replace parts of the block chain to roll back their own spends.
