Day: June 26, 2015

How to Make a Paper Bitcoin Wallet

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One of the most popular options for keeping your bitcoins safe is something called a paper wallet. Here we explain how to transfer all those digital coins into a physical paper form using just a printer.

Note that in this guide we’ll be talking about bitcoin. However, the basic concepts apply to any other cryptocurrency; for example, litecoin.

What is a wallet and why do I need one?

bitcoinpaperwalletA bitcoin wallet consists of two keys. The one you’ll already likely be familiar with is the public key, which is your wallet address and is how other people send bitcoins to you.

The other part of your bitcoin wallet is the private key. It is this that enables you to send bitcoins to other people.

The combination of the recipient’s public key and your private key is what makes a cryptocurrency transaction possible.

It is important to understand that, if anyone else obtains the private key of your wallet, they can withdraw your funds – this is why it’s absolutely essential that nobody else discovers it.

So, if you keep your coins in either an online wallet, or a hard-drive-based software wallet, you are vulnerable to attacks by hackers or malware that can log your keystrokes.

Furthermore, a stolen PC or a hard-drive crash could also see you waving bye-bye to your digital treasure.

Used with care, a paper wallet can protect you from these possibilities.

What is a paper wallet?

litecoinwalletA paper wallet is a document that contains copies of the public and private keys that make up a wallet. Often it will have QR codes, so that you can quickly scan them and add the keys into a software wallet to make a transaction.

The benefit of a paper wallet is that the keys are not stored digitally anywhere, and are therefore not subject to cyber-attacks or hardware failures.

The disadvantage of a paper wallet is that paper and ink can degrade, and paper is relatively fragile – its definitely worth keeping well away from fire and water for obvious reasons.

Furthermore, if you lose a paper wallet, you’ll never be able to access the bitcoins sent to its address.

Creating a paper wallet

Here are 10 steps needed to create a paper wallet:

  1. To generate a new bitcoin address, open BitAddress.org in your browser (orLiteAddress.org for litecoin).
  2. BitAddress (but not LiteAddress) will ask you to create some randomness by either randomly typing characters into the form or moving your cursor around.
  3. You will be presented with your public and private keys and their respective QR codes. Do not scan these.
  4. Click the Paper wallet tab.
  5. Select the number of addresses to generate.
  6. If you dont wish to keep the bitcoin artwork, click the Hide art? button.
  7. Click the Generate button to create new wallets.
  8. Once the wallets are generated, click the Print button to make a hard copy.
  9. Your browser will ask you to select the printer you wish to use. In the case of Google Chrome, you may also save the page as a PDF file.
  10. Make a note of the public addresses, or scan the public address QR code in your bitcoin (or litecoin) app and start depositing funds.

For users of the Blockchain.info website, there is also a basic paper wallet option too. Click on the Import/Export option, and look for the Paper wallet link on the left-hand menu.

A much more sophisticated option for your paper wallet can be found atBitcoinpaperwallet.com.

This website offers a tamper-resistant design of paper wallet. It is also possible to order holographic labels to demonstrate that the wallet hasn’t been tampered with. It also supplies a live-boot Ubuntu CD with paper-wallet software pre-installed.

Security Concerns

shutterstock_82383217Given the implications and risks of storing large amounts of money, you may want to take serious precautions for how to go about creating your paper wallet and storing it afterwards.

  • Do not let anyone see you create your wallet.
  • BitAddress and LiteAddress both support encryption of private keys through the BIP38 algorithm. This provides two factor authentication for your paper wallet; ie: something you have (the paper wallet), and something you know (the passphrase). Also note, that you will have to use the same website in the future to decrypt the private key.
  • To rule out the risk of any sort of spyware monitoring your activity, you should use a clean operating system. A good way to achieve this would be to create a USB flash drive or DVD with a LiveCD Linux distribution, such as Ubuntu.
  • Furthermore, once a paper-wallet has been set up via a website, it should be possible for the website code to run offline. Therefore, before creating the private and public keys, take your computer offline before generating the keys.
  • For ultra-tight security, print the paper wallet from a printer that is not connected to a network.

shutterstock_169671383Tips for keeping your paper wallet safe

  • Store the paper wallet in a sealed plastic bag to protect against water or damp.
  • If your paper wallet isn’t folded you could laminate it for durability and proof against water.
  • If you have one, store your paper wallet in a safe to protect from theft and fire.
  • You could entrust the paper wallet with a solicitor. For example, the person who holds your last will & testament.
  • For added redundancy, you may store a wallet in several locations. Some bitcoiners use trusted family members, others use deposit boxes.

Exporting private keys from altcoin wallets

If you want to create a paper wallet for a lesser-used currency that doesn’t have an address generator website, there is still a way to achieve this.

What every alt-currency does have is a variation of the Bitcoin-Qt wallet application.

  • Goto the Receive tab, where your wallet addresses are listed.
  • Right-click on the address you wish to save, then copy the address to the clipboard.
  • Click the Help menu and select Debug’.
  • In the Console tab, enter dumpprivkey and paste in the wallet address.

The console will then display the private key of that wallet.

You then have the public and private keys of the wallet. You can print these as is, or you can opt to generate QR codes to print.

However, the wallet details will still exist in your computer. The only way to remove them it is to open your file explorer in the C:\Users\[YourUsername]\AppData\Roaming\[Wallet App Name]\ folder and delete the wallet.dat file.

NOTE: this will remove all addresses held in the software wallet, and you should make sure that there are no funds remaining in the other addresses you will be deleting.

Now you should be the proud owner of an unhackable paper wallet for your digital currency. If a paper wallet is not for you, however, you could use your own mind with a brain wallet.

Wallet, lock icons and printer images via Shutterstock

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How Does Cloud Mining Bitcoin Work?

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If you want to invest in bitcoin mining without the hassle of managing your own hardware, there is an alternative. You can use the cloud to earn your coins.

Put very simply, cloud mining means using (generally) shared processing power run from remote data centres. One only needs a home computer for communications, optional local bitcoin wallets and so on.

However, there are certain risks associated with cloud mining that investors need to understand prior to purchase.

Pros

Here’s why you might want to consider cloud mining:

  • A quiet, cooler home – no constantly humming fans
  • No added electricity costs
  • No equipment to sell when mining ceases to be profitable
  • No ventilation problems with hot equipment
  • Reduced chance of being let down by mining equipment suppliers.

Cons

Here’s why you might not want to consider cloud mining:

  • Risk of fraud
  • Opaque mining operations
  • Less fun (if you’re a geek who likes system building!)
  • Lower profits – the operators have to cover their costs after all
  • Contractual warnings that mining operations may cease depending on the price of bitcoin
  • Lack of control and flexibility.

Types of cloud mining

In general, there are three forms of remote mining available at the moment:

  1. Hosted mining
    Lease a mining machine that is hosted by the provider.
  2. Virtual hosted mining
    Create a (general purpose) virtual private server and install your own mining software.
  3. Leased hashing power
    Lease an amount of hashing power, without having a dedicated physical or virtual computer. (This is, by far, the most popular method of cloud mining.)

How to determine profitability

shutterstock_123406111We have previously covered ways to calculate mining profitability. However, the web services offered are designed to work with your hardware parameters, not cloud-mining parameters.

Even so, you can still use these calculators by thinking clearly about the costs involved. Profitability calculators (for example, The Genesis Block) often ask for your electricity costs, and sometimes the initial investment in hardware. Effectively, you are being asked for your ongoing costs and your one-off investments.

Therefore, since the provider, not you, is paying the electricity bills, you can enter the monthly mining bill in place of the electricity cost.

The conversion process isn’t completely straightforward, though. In the case of hardware miners, you can work out the monthly running cost by multiplying your electricity charge (ie: $ per KWh) by the power consumption of the unit and by a conversion factor of 0.744 (the ratio of seconds per month to joules of energy per KWh).

But, for cloud mining calculations, you need to do the opposite, because the provider gives you an (effective) monthly running cost. Hence, you need to calculate an equivalent cost per kilowatt hour to feed into the mining calculator. This is done bydividing (not multiplying) the monthly running cost by the 0.744 conversion factor mentioned above.

Risk vs reward

shutterstock_143906389When engaging in any type of cryptocurrency mining there are risks, but profitability is possible if you make the right choices. In this article, we’ve given you some pointers on how to decide which way to go.

In your test calculations, you will likely see that some cloud mining services will be profitable for a few months, but, as the difficulty level of bitcoin increases, you would probably start to make a loss in four to six months and beyond.

A possible remedy to this situation is to reinvest what you have made into maintaining a competitive hashing rate, but this is highly speculative.

As mentioned above, the risk of fraud and mismanagement is all too common in the cloud mining space. Investors should only invest in cloud mining if they are comfortable with these risks – as the saying goes, never invest more than you are willing to lose.

Investigate social media channels, speak with former customers and ask pointed questions of operators prior to investing. Ultimately, you should practice the same kind of due diligence that you would for any investment.

Disclaimer: This article should not be viewed as an endorsement of any of the services mentioned. Please do your own research before considering investing any funds via these services.

Australian mineserver roomaccounting and reward and risk images via Shutterstock

How to Set Up a Bitcoin Miner

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There are three main categories of bitcoin mining hardware, each more expensive and more powerful than the last. This guide to setting up a bitcoin miner explains each of them, and talks about how to make them work.

Hot to Mine Bitcoin

By this stage, you will understand how bitcoin works, and what mining means. But we need to get from theory to practice. How can you set up a bitcoin mining hardware and start generating some digital cash? The first thing you’re going to need to do is decide on your hardware, and there are two main things to think about when choosing it:

Hash rate

This is the number of calculations that your hardware can perform every second as it tries to crack the mathematical problem we described in our mining section. Hash rates are measured in megahashes, gigahashes, and terahashes per second (MH/sec, GH/sec, and TH/sec. The higher your hash rate (compared to the current average hash rate), the more likely you are to solve a transaction block. The bitcoin wiki’s mining hardware comparison page is a good place to go for rough information on hash rates for different hardware.

Energy consumption

How to set up a bitcoin minerAll this computing power chews up electricity, and that costs money. It’s worth looking at your hardware’s energy consumption in watts, when making your choice. You want to make sure that you don’t end up spending all of your money on electricity to mine coins that won’t be worth what you paid.

Use these two factors to work out how many hashes you’re getting for every watt of electricity that you use. To do this, divide the hash count by the number of watts.

For example, if you have a 500 GH/sec device, and it’s taking 400 watts of power, then you’re getting 1.25 GH/sec per watt. You can check your power bill or use an electricity price calculator online to find out how much that means in hard cash.

However, there’s a caveat here. In some cases, you’ll be using your computer to run the mining hardware. Your computer has its own electricity draw on top of the mining hardware, and you’ll need to factor that into your calculation.

Bitcoin Mining Hardware

There are three main hardware categories for bitcoin miners: GPUs, FPGAs, and ASICs. We’ll explore them in depth below.

CPU/GPU Bitcoin Mining

The least powerful category of bitcoin mining hardware is your computer itself. Theoretically, you could use your computer’s CPU to mine for bitcoins, but in practice, this is so slow by today’s standards that there isn’t any point.

You can enhance your bitcoin hash rate by adding graphics hardware to your desktop computer. Graphics cards feature graphical processing units (GPUs). These are designed for heavy mathematical lifting so they can calculate all the complex polygons needed in high-end video games. This makes them particularly good at the SHA hashing mathematics necessary to solve transaction blocks.

You can buy GPUs from two main vendors: ATI and Nvidia. High-end cards can cost hundreds of dollars, but also give you a significant advantage over CPU hashing. For example, an ATI 5970 graphics card can give you over 800 MH/sec compared with a CPU, which will generally give you less than 10 MH/sec.

One of the nice things about GPUs is that they also leave your options open. Unlike other options discussed later, these units can be used with cryptocurrencies other than bitcoin. Litecoin, for example, uses a different proof of work algorithm to bitcoin, called Scrypt. This has been optimized to be friendly to CPUs and GPUs, making them a good option for GPU miners who want to switch between different currencies.

GPU mining is largely dead these days. Bitcoin mining difficulty has accelerated so much with the release of ASIC mining power that graphics cards can’t compete. If you do want to use them, you’d best equip yourself with a motherboard that can take multiple boards, to save on running separate PSUs for different boards.

FPGA Bitcoin Mining

A Field Programmable Gate Array is an integrated circuit designed to be configured after being built. This enables a mining hardware manufacturer to buy the chips in volume, and then customize them for bitcoin mining before putting them into their own equipment. Because they are customized for mining, they offer performance improvements over CPUs and GPUs. Single-chip FPGAs have been seen operating at around 750 Megahashes/sec, although that’s at the high end. It is of course possible to put more than one chip in a box.

ASIC Bitcoin Miners

This is where the action’s really at. Application Specific Integrated Circuits (ASICs) are specifically designed to do just one thing: mine bitcoins at mind-crushing speeds, with relatively low power consumption. Because these chips have to be designed specifically for that task and then fabricated, they are expensive and time-consuming to produce – but the speeds are stunning. At the time of writing, units are selling with speeds anywhere from 5-500 Gigahashes/sec (although actually getting some of them to them to ship has been a problem). Vendors are already promising ASIC devices with far more power, stretching up into the 2 Terahashes/sec range.

Read the latest news on bitcoin mining developments and companies.

Calculate mining profitability

calculatingBefore making your purchase, calculate the projected profitability of your miner, using the excellent mining profitability calculator from The Genesis Block or this one. You can input parameters such as equipment cost, hash rate, power consumption, and the current bitcoin price to see how long it will take to pay back your investment.

One of the other key parameters here is network difficulty. This metric determines how hard it is to solve transaction blocks, and it varies according to the network hash rate. Difficulty is likely to increase substantially as ASIC devices come on the market, so it might be worth increasing this metric in the calculator to see what your return on investment will be like as more people join the game. Use this guide on calculating mining profitability for more information.

Once you have chosen your hardware, you’ll need to do several other things:

Download the software

Depending on which equipment you choose, you will need to run software to make use of it. Typically when using GPUs and FPGAs, you will need a host computer running two things: the standard bitcoin client, and the mining software.

Standard bitcoin client

This software connects your computer to the network and enables it to interact with the bitcoin clients, forwarding transactions and keeping track of the block chain. It will take some time for it to download the entire bitcoin block chain so that it can begin. The bitcoin client effectively relays information between your miner and the bitcoin network.

Bitcoin mining software

The bitcoin mining software is what instructs the hardware to do the hard work, passing through transaction blocks for it to solve. There are a variety of these available, depending on your operating system. They are available for Windows, Mac OS X, and others.

You may well need mining software for your ASIC miner, too, although some newer models promise to ship with everything pre-configured, including a bitcoin address, so that all you need to do is plug it in the wall.

One smart developer even produced a mining operating system designed to run on the Raspberry Pi, a low-cost credit card-sized Linux computer designed to consume very small amounts of power. This could be used to power a USB-connected ASIC miner.

Join a pool

Now, you’re all set up. Good for you. I bet you thought you were going to be mining more bitcoins than the Federal Reserve prints dollars, didn’t you? Sadly not. You will stand little chance of success mining bitcoins unless you work with other people. You can find out more about that in our upcoming guide on how to join a mining pool.

Who is Satoshi Nakamoto?

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Who is Satoshi Nakamoto?

who is Satoshi Nakamoto

 

 

 

 

 

 

 

 

While we may not know who he (or she) was, we know what he did. He was the inventor of the bitcoin protocol, publishing a paper via the Cryptography Mailing List in November 2008.

He then released the first version of the bitcoin software client in 2009, and participated with others on the project via mailing lists, until he finally began to fade from the community toward the end of 2010.

He worked with people on the open-source team, but took care never to reveal anything personal about himself, and the last anyone heard from him was in the spring of 2011, when he said that he had “moved on to other things”.

But he was Japanese, right?

Best not to judge a book by its cover.Or in fact, maybe we should.

“Satoshi” means “clear thinking, quick witted; wise”. “Naka” can mean “medium, inside, or relationship”. “Moto” can mean “origin”, or “foundation”.

Those things would all apply to the person who founded a movement by designing a clever algorithm. The problem, of course, is that each word has multiple possible meanings.

We can’t know for sure whether he was Japanese or not. In fact, it’s rather presumptuous to assume that he was actually a ‘he’.

We’re just using that as a figure of speech, but allowing for the fact that this could have been a pseudonym, ‘he’ could have been a ‘she’, or even a ‘they’.

Does anyone know who Nakamoto was?

No, but the detective techniques that people use when guessing are sometimes even more intriguing than the answer. The New Yorker’s Joshua Davis believed that Satoshi Nakamoto was Michael Clear, a graduate cryptography student at Dublin’s Trinity College.

He arrived at this conclusion by analyzing 80,000 words of Nakamoto’s online writings, and searching for linguistic clues. He also suspected Finnish economic sociologist and former games developer Vili Lehdonvirta.

Both have denied being bitcoin’s inventor. Michael Clear publicly denied being Satoshi at the 2013 Web Summit.

anonymous group of peopleAdam Penenberg at FastCompany disputed that claim, arguing instead that Nakamoto may actually have been three people: Neal King, Vladimir Oksman, and Charles Bry. He figured this out by typing unique phrases from Nakamoto’s bitcoin paper into Google, to see if they were used anywhere else.

One of them, “computationally impractical to reverse,” turned up in a patent application made by these three for updating and distributing encryption keys. The bitcoin.org domain name originally used by Satoshi to publish the paper had been registered three days after the patent application was filed.

It was registered in Finland, and one of the patent authors had traveled there six months before the domain was registered. All of them deny it. Michael Clear also publicly denied being Satoshi at the 2013 Web Summit.

In any case, when bitcoin.org was registered on August 18th 2008, the registrant actually used a Japanese anonymous registration service, and hosted it using a Japanese ISP. The registration for the site was only transferred to Finland on May 18th 2011, which weakens the Finland theory somewhat.

Others think that it was Martii Malmi, a developer living in Finland who has been involved with bitcoin since the beginning, and developed its user interface.

A finger has also been pointed at Jed McCaleb, a lover of Japanese culture and resident of Japan, who created troubled bitcoin exchange Mt. Gox and co-founded decentralized payment systems Ripple and later Stellar.

Another theory suggests that computer scientists Donal O’Mahony and Michael Peirceare Satoshi, based on a paper that they authored concerning digital payments, along with Hitesh Tewari, based on a book that they published together. O’Mahony and Tewari also studied at Trinity College, where Michael Clear was a student.

Israeli scholars Dorit Ron and Adi Shamir of the Weizmann Institute retracted allegations made in a paper suggesting a link between Satoshi and Silk Road, the black market web site that was taken down by the FBI in October 2013. They had suggested a link between an address allegedly owned by Satoshi, and the site. Security researcher Dustin D. Trammell owned the address, and disputed claims that he was Satoshi.

In May 2013, Internet pioneer Ted Nelson threw another hat into the ring: Japanese mathematician Professor Shinichi Mochizuki, although he admits that the evidence is circumstantial at best.

In February 2014, Newsweek’s Leah McGrath Goodman claimed to have tracked down the real Satoshi Nakamoto. Dorian S Nakamoto has since denied he knows anything about bitcoin, eventually hiring a lawyer and releasing an official statement to that effect.

Dorian Satoshi Nakamoto
No, Satoshi Nakamoto is not a 64-year-old Japanese man living in California, probably…

Hal Finney, Michael Weber, Wei Dai and several other developers were among those who are periodically named in media reports and online discussions as potential Satoshis. A group of forensic linguistics experts from Aston University believe the real creator of bitcoin is Nick Szabo, based upon analysis of the Bitcoin White Paper.

Dominic Frisby, a comedian and a writer, also suggests that BitGold creator Szabo was the most likely candidate to be Satoshi in his book, “Bitcoin: The Future of Money”. His detailed analysis involved the linguistics of Satoshi’s writing, judging the level of technical skill in C++ and even Satoshi’s likely birthday.

In Nathaniel Popper’s book, ‘Digitial Gold‘, released in May 2015, Popper reveals that in a rare encounter at an event Szabo again denied that he was Satoshi.

For the most part, all of these potential Satoshi’s have insisted they are not Nakamoto. Michael Weber has not yet responded to Business Insider’s article.

So what do we know about him?

One thing we know, based on interviews with people that were involved with him at an early stage in the development of bitcoin, is that he thought the system out very thoroughly.

His coding wasn’t conventional, according to core developer Jeff Garzik, in that he didn’t apply the same rigorous testing that you would expect from a classic software engineer.

How rich is he?

many bitcoin coins
zcopley / Flickr

An analysis by Sergio Lerner, an authority on bitcoin and cryptography, suggests that Satoshi mined many of the early blocks in the bitcoin network, and that he had built up a fortune of around 1 million unspent bitcoins. That hoard would be worth $1bn at November 2013’s exchange rate of $1,000.

What is he doing now?

No one knows what Satoshi is up to, but one of the last emails he sent to a software developer, dated April 23 2011, said “I’ve moved on to other things. It’s in good hands with Gavin and everyone.”

Did he work for the government?

There are rumors, of course. People have interpreted his name as meaning “central intelligence”, but people will see whatever they want to see. Such is the nature of conspiracy theories.

The obvious question would be why one of the three-letter agencies would be interested in creating a cryptocurrency that would subsequently be used as an anonymous trading mechanism, causing senators and the FBI alike to wring their hands about potential terrorism and other criminal endeavours. No doubt conspiracy theorists will have their views on that, too.

Perhaps it doesn’t matter. Core developer Jeff Garzik puts it succinctly. “Satoshi published an open-source system for the purpose that you didn’t have to know who he was, and trust who he was, or care about his knowledge,” he points out. Open-source code makes it impossible to hide secrets. “The source code spoke for itself.”

Moreover, it was smart to use a pseudonym, he argues, because it forced people to focus on the technology itself rather than on the personality behind it. At the end of the day, bitcoin is now far bigger than Satoshi Nakamoto.

Having said that, if the real Satoshi Nakamoto is out there – get in touch!

Sakamoto image via (AP Photo/Damian Dovarganes)

How do Bitcoin Transactions Work?

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Bitcoin transactions are sent from and to electronic bitcoin wallets, and are digitally signed for security. Everyone on the network knows about a transaction, and the history of a transaction can be traced back to the point where the bitcoins were produced.

Holding onto bitcoins is great if you’re a speculator waiting for the price to go up, but the whole point of this currency is to spend it, right? So, when spending bitcoins, how do transactions work?

There are no bitcoins, only records of bitcoin transactions

Here’s the funny thing about bitcoins: they don’t exist anywhere, even on a hard drive. We talk about someone having bitcoins, but when you look at a particular bitcoin address, there are no digital bitcoins held in it, in the same way that you might hold pounds or dollars in a bank account. You cannot point to a physical object, or even a digital file, and say “this is a bitcoin”.

Instead, there are only records of transactions between different addresses, with balances that increase and decrease. Every transaction that ever took place is stored in a vast public ledger called the block chain. If you want to work out the balance of any bitcoin address, the information isn’t held at that address; you must reconstruct it by looking at the blockchain.

What does a transaction look like?

If Alice sends some bitcoins to Bob, that transaction will have three pieces of information:

  • An input. This is a record of which bitcoin address was used to send the bitcoins to Alice in the first place (she received them from her friend, Eve).
  • An amount. This is the amount of bitcoins that Alice is sending to Bob.
  • An output. This is Bob’s bitcoin address.

How is it sent?

How do bitcoin transactions workTo send bitcoins, you need two things: a bitcoin address and a private key. A bitcoin address is generated randomly, and is simply a sequence of letters and numbers. The private key is another sequence of letters and numbers, but unlike your bitcoin address, this is kept secret.

Think of your bitcoin address as a safe deposit box with a glass front. Everyone knows what is in it, but only the private key can unlock it to take things out or put things in.

When Alice wants to send bitcoins to Bob, she uses her private key to sign a message with the input (the source transaction(s) of the coins), amount, and output (Bob’s address).

She then sends them from her bitcoin wallet out to the wider bitcoin network. From there, bitcoin miners verify the transaction, putting it into a transaction block and eventually solving it.

Why must I sometimes wait for my transaction to clear?

Because your transaction must be verified by miners, you are sometimes forced to wait until they have finished mining. The bitcoin protocol is set so that each block takes roughly 10 minutes to mine.

Some merchants may make you wait until this block has been confirmed, meaning that you may have to make a cup of coffee and come back again in a short while before you can download the digital goods or take advantage of the paid service.

On the other hand, some merchants won’t make you wait until the transaction has been confirmed. They effectively take a chance on you, assuming that you won’t try and spend the same bitcoins somewhere else before the transaction confirms. This often happens for low value transactions, where the risk of fraud isn’t as great.

What if the input and output amounts don’t match?

Because bitcoins exist only as records of transactions, you can end up with many different transactions tied to a particular bitcoin address. Perhaps Jane sent Alice two bitcoins, Philip sent her three bitcoins and Eve sent her a single bitcoin, all as separate transactions at separate times.

These are not automatically combined in Alice’s wallet to make one file containing six bitcoins. They simply sit there as different transaction records.

When Alice wants to send bitcoins to Bob, her wallet will try to use transaction records with different amounts that add up to the number of bitcoins that she wants to send Bob.

The chances are that when Alice wants to send bitcoins to Bob, she won’t have exactly the right number of bitcoins from other transactions. Perhaps she only wants to send 1.5 BTC to Bob.

None of the transactions that she has in her bitcoin address are for that amount, and none of them add up to that amount when combined. Alice can’t just split a transaction into smaller amounts. You can only spend the whole output of a transaction, rather than breaking it up into smaller amounts.

Instead, she will have to send one of the incoming transactions, and then the rest of the bitcoins will be returned to her as change.

Alice sends the two bitcoins that she got from Jane to Bob. Jane is the input, and Bob is the output. But the amount is only 1.5 BTC, because that is all she wants to send. So, her wallet automatically creates two outputs for her transaction: 1.5 BTC to Bob, and 0.5 BTC to a new address, which it created for Alice to hold her change from Bob.

Are there any transaction fees?

Sometimes, but not all the time.

Transaction fees are calculated using various factors. Some wallets let you set transaction fees manually. Any portion of a transaction that isn’t picked up by the recipient or returned as change is considered a fee. This then goes to the miner lucky enough to solve the transaction block as an extra reward.

Right now, many miners process transactions for no fees. As the block reward for bitcoins decreases, this will be less likely.

One of the frustrating things about transaction fees in the past was that the calculation of those fees was complex and arcane. It has been the result of several updates to the protocol, and has developed organically.

Updates to the core software handling bitcoin transactions will see it change the way that it handles transaction fees, instead estimating the lowest fee that will be accepted.

Can I get a receipt?

ReceiptBitcoin wasn’t really meant for receipts. Although there are changes coming in version 0.9 that will alter the way payments work, making them far more user-friendly and mature.

Payment processors like BitPay also provide the advanced features that you wouldn’t normally get with a native bitcoin transaction, such as receipts and order confirmation web pages.

What if I only want to send part of a bitcoin?

Bitcoin transactions are divisible. A satoshi is one hundred millionth of a bitcoin, and it is possible to send a transaction as small as 5430 satoshis on the bitcoin network.

How to Sell Bitcoin

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Selling bitcoin isn’t quite as straightforward as buying bitcoin, but fortunately CoinDesk is here to help. This guide will give you all the information you need to cash out your digital currency.

When deciding how to sell your bitcoin, you first need to consider which method best suits your situation: selling bitcoin online or selling bitcoin in person. Each option has its own advantages and disadvantages.

Selling bitcoin online

Selling bitcoin online is by far the more common way of trading your bitcoin. There are now three ways to go about selling bitcoin online.

1. The first way involves a direct trade with another person, an intermediary facilitating the connection.

2. The second way is through an online exchange, where your trade is with the exchange rather than another individual.

3. New peer-to-peer trading marketplaces that allow bitcoin owners to obtain discounted goods with their bitcoin via others that want to obtain the cryptocurrency with credit/debit cards. The two groups are brought together to solve both problems in a kind of peer-to-peer exchange.

1. Direct trades: Websites that offer this type of selling structure include Coinbase andLocalBitcoins in the US, and BitBargain UK and Bittylicious in the UK.

On these sites, you will usually have to register as a seller. This involves verifying your identity, which we will discuss again later. Once you have registered, you can post an offer, signalling that you want to sell, and the website will alert you when a buyer wants to trade with you. From there, your interaction is solely with the buyer, but you use the website to complete your trade.

The process of selling on Bitbargain UK and (more so) Bittylicious can be quite involved and requires some patience. However, support at the former site has been great in our experience. Bitcoin users with bank accounts in the United States should consider usingCoinbase or Circle, which has won many fans with its simplicity.

Bitcoin can be traded with other currencies

2. Exchange trades: The other way to sell bitcoins is to register with an online exchange. You will still have to verify your identity, but in this case you won’t have to do as much work when it comes to organizing the sale.

Exchanges act as an intermediary who holds everyone’s funds. You place a ‘sell order’ (just as you would place a buy order), stating the volume (amount) and type of currency you wish to sell (eg bitcoin), and the price per unit you wish to sell for.

As soon as someone places a matching buy order, the exchange will complete the transaction. The currency will then be credited to your account.

The downside that accompanies this ease of use is that, if you are selling bitcoin for fiat currencies, you will need to withdraw those funds to your bank. If the exchange is facing liquidity problems or issues with its banks, it can take an inordinate amount of time to receive your funds.

Mt. Gox became infamous for this problem before it went bankrupt, and BTC-e has recently been plagued with reports of similar difficulties. Therefore, you should carefully research the exchange you intend to use before committing funds.

Examples of other crypto-to-fiat currency exchanges includeCircleKraken and Bitstamp.

Alternatively, you could use a pure cryptocurrency exchange to change bitcoin for another cryptocurrency. It’s less likely that anyone would want to do this, but there are reasons such as arbitrage, or the rare occasion if a shop accepts something other than bitcoin (for example, Bitcoin Shop now accepts litecoin and dogeoin too, for a wide range of goods).

Examples of these types of sites are: BTER, CoinCorner and Cryptsy.

In addition, you’ll have to pay a fee to use some exchanges. BTC-e charges a flat 0.2%. For overviews of what fees are charged by the various cyrptocurrency markets and what volumes are being traded, see CoinCompare and Bitcoin Charts for up-to-date information.

Another consideration is that there will be some limit to the amount of money you are allowed to store (subject to change over time) on an exchange. Regardless, it is not wise to use exchanges to store your entire pot of coins, even though it can appear to be the easy option if all you are doing is speculating.

You should take responsibility for your own funds, and store any unneeded amounts on your own devices or offline, rather than trusting an exchange that might one day be hacked.

3. Peer-to-peer trading marketplaces

A new development in the bitcoin space is the advent of sites like Brawkerand Purse, which set out to bring together two groups of people with specific and complementary needs.

The first group are individuals who want to be able to use bitcoin to buy goods from sites which do not yet directly accept digital currencies. The second comprises of others who would like to buy bitcoin with a credit or debit card. The marketplace brings together individuals with matching requirements to effectively sell bitcoin to one and provide discounted goods for the other.

The marketplace acts as an intermediary, offering users the platform, bitcoin wallet and escrow for transactions.

How it works:

  1. Alice posts her required Amazon wish list on the marketplace, stating the discount she would like (normally up to 25%).
  2. Bob has a credit/debit card and wants to buy bitcoin matching the value of Alice’s purchase(s). He accepts the trade and, through the marketplace, buys the Amazon goods and requests they be delivered to Alice’s address.
  3. Once the goods are delivered, Alice notifies the marketplace and Bob’s bitcoin are released from escrow and arrive in his wallet, minus Alice’s agreed discount and a small fee for the marketplace.

This system does mean that Bob will be paying a relatively high fee for the service, but also means he will be easily able to acquire bitcoin via bank card.

Concerns with withdrawing funds

The universal way to move money around the world is international wire transfers. Most (if not all) online bitcoin markets support this method of transferral.

Withdrawing Funds from Bitcoin Exchanges

Another way to transfer money to your bank after selling bitcoin is via the “Single European Payments Area” (SEPA) system. SEPA was designed to make international transfers between member states of the European Union more efficient. Some exchanges (such as Kraken and BTC-e) support these payments.

However, transfers take a very long time (around four days), and can incur large charges – potentially making trading prohibitively expensive. HSBC, for example, charges £4 per SEPA payment made via online banking and £9 per WorldPay transaction. Barclays charges £15 per SEPA payment and £25 for other international transactions.

If you are opening an account with the specific purpose of receiving funds from bitcoin trading, you may find high street banks refuse to do business with you. HSBC has explicitly refused the author of this guide accounts for bitcoin trading.

You can also use third-party payment processors to withdraw and receive fiat funds. The numbers of these services is dwindling, however. OKpay recently stopped engaging with bitcoin businesses.

Identity verification

Identity Verification for Bitcoin SellersWhile many of the bitcoin markets mentioned here require very little identification from buyers, they require a lot of proof of identity from sellers. There are few legal requirements from bitcoin markets to record who their users are, but most (if not all) are preemptively collecting identity data in anticipation of forthcoming regulations.

To make becoming a seller easier, it is worth at least considering completing the identity verification process when you first join the site. Getting this step out of the way can remove barriers to selling if and when you’re ready to make the move.

Expect markets to ask you to upload scans of two utility bills displaying your name and address, along with a photo ID (such as a passport or driving licence). Some (such as BitBargain UK) may even ask you to take a selfie including your photo ID and the name of the market on a piece of paper!

If you are not comfortable uploading such personal documents to an (effectively) untrusted business, then you will have a difficult time finding somewhere to sell bitcoin online.

2. Selling bitcoin in person

How to Sell Bitcoin in Person

Selling bitcoin in person can, in many ways, be the easiest way to pass on your digital currency. Simply scanning a QR code on another person’s phone and accepting cash-in-hand is about as easy as a bitcoin transaction can get.

If you have friends or family who want to buy bitcoin, the process is simple. Set them up with a bitcoin wallet, send them the bitcoins and collect your cash.

There are several things to be aware of when selling bitcoin in person.

Agree on a price: Decide on a rate works for you.

  • Many use a price from a prominent bitcoin exchange, or the CoinDesk Bitcoin Price Index.
  • Some sellers apply a percentage on top of these rates to cover costs and as a convenience/anonymity premium.
  • You could use a mobile app to calculate prices. Popular apps include Zeroblock and BTCreport.
  • It helps to be aware of local fluctuations in price. Price can vary from country to country, often due to difficulties in obtaining bitcoin with the local national currency.
  • There are many bitcoin meetups around the world where people are happy to trade bitcoin and other cryptocurrencies.

Stay safe 

  • It is always wise when carrying a large amount of cash to meet in a public place and/or go with a friend.

LocalBitcoins

  • Alternatively, you could advertise yourself as a bitcoin seller to a wider audience. The definitive site for this is LocalBitcoins. This website allows users to rate each other, so one may assess the trustworthiness of a potential trade partner. You may be able to sell with a premium attached once you have a reliable reputation.
  • You do not need to verify your identity as on other sites.
  • Again, if you are setting yourself up for an in-person meeting using LocalBitcoins, you must always think about the general safety rules for meeting a stranger from the Internet.
  • LocalBitcoins also supports escrow transactions, however, these are for online transactions, not face-to-face deals. Therefore, do not comply with requests for someone who asks for escrow for a face-to-face transaction.

How to Store Your Bitcoins

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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.

Bitcoin paper, coin and USB wallets
Bitcoin paper, coin and USB wallets

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 walletcomes 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, Xapoand 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 apppulled 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.

Aegis Wallet Wear Moto 360
The Aegis Bitcoin Wallet even supports android smartwatches

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

Trezor Bitcoin Wallet CoinDesk
The Trezor hardware wallet is available from $119 directly or from Amazon.

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

ledger-wallet-nano-review-vires-keyboard
The Ledger Wallet Nano is Available driect for €34.80 and also from Overstock

The compact Ledger USB Bitcoin Wallet uses smartcard security and is available for areasonable price. CoinDesk reviewed this wallet in December 2014.

Mycelium, Cryptolabs and BitStash currently have a hardware wallets in development, but, as of December 2014 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.

Product Review Price
coinbaseLedger Nano Ledger Review €34.80 BUY ONLINE
coinbaseSatoshiLabs Trezor Trezor Review $119 BUY ONLNE

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.

A bitcoin paper wallet
A bitcoin paper wallet

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.

To find out more about creating a paper wallet, read our tutorial.

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

Safe with cash insideIf 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