A condition in which more than half the computing power on a cryptocurrency network is controlled by a single miner or group of miners. That amount of power theoretically makes them the authority on the network. This means that every client on the network believes the attacker’s hashed transaction block. This gives them control over the network, including the power to:
Issue a transaction that conflicts with someone else’s.
Stop someone else’s transaction from being confirmed.
Spend the same coins multiple times.
Prevent other miners from mining valid blocks.
A bitcoin address is used to receive and send transactions on the bitcoin network. It contains a string of alphanumeric characters, but can also be represented as a scannable QR code. A bitcoin address is also the public key in the pair of keys used by bitcoin holders to digitally sign transactions (see Public key).
The collective name for cryptocurrencies offered as alternatives to bitcoin. Litecoin, Feathercoin, W2Coin and PPcoin are all altcoins.
Anti-Money Laundering techniques are used to stop people converting illegally obtained funds, to appear as though they have been earned legally. AML mechanisms can be legal or technical in nature. Regulators frequently apply AML techniques to bitcoin exchanges.
An Application Specific Integrated Circuit is a silicon chip specifically designed to do a single task. In the case of bitcoin, they are designed to process SHA-256 hashing problems to mine new bitcoins.
A piece of equipment containing an ASIC chip, configured to mine for bitcoins. They can come in the form of boards that plug into a backplane, devices with a USB connector, or standalone devices including all of the necessary software, that connect to a network via a wireless link or ethernet cable.
Bitcoin Investment Trust
This private, open-ended trust invests exclusively in bitcoins and uses a state-of-the-art protocol to store them safely on behalf of its shareholders.
It provides a way for people to invest in bitcoin without having to purchase and safely store the digital currency themselves.
Bitcoin Price Index (BPI)
The CoinDesk Bitcoin Price Index represents an average of bitcoin prices across leading global exchanges that meet criteria specified by the BPI. There is also an API for developers to use.
The bitcoin whitepaper was written by ‘Satoshi Nakamoto’ and posted to a Cryptography Mailing list in 2008. The paper describes the bitcoin protocol in detail, and is well worth a read. Satoshi Nakamoto followed this by releasing the bitcoin code in 2009.
A payment processor for bitcoins, which works with merchants, enabling them to take bitcoins as payment.
An exchange for bitcoins that has been gaining in popularity. Read the latest Bitstamp news.
The full list of blocks that have been mined since the beginning of the bitcoin cryptocurrency. The block chain is designed so that each block contains a hash drawing on the blocks that came before it. This is designed to make it more tamperproof.
The reward given to a miner which has successfully hashed a transaction block. This can be a mixture of coins and transaction fees, depending on the policy used by the cryptocurrency in question, and whether all of the coins have already been successfully mined. Bitcoin currently awards 25 bitcoins for each block. The block reward halves when a certain number of blocks have been mined. In bitcoin’s case, the threshold is every 210,000 blocks.
The short currency abbreviation for bitcoins.
A project founded by bitcoin enthusiast Josh Rossi, to form a public outcry bitcoin exchange in New York’s Union Square. Named after the Buttonwood agreement, which formed the basis for the New York Stock Exchange in 1792.
A software program running on a desktop or laptop computer, or mobile device. It connects to the bitcoin network and forwards transactions. It may also include a bitcoin wallet (see node).
The act of hashing a bitcoin transaction successfully into a transaction block, and cementing its validity. A single confirmation will take around 10 minutes, which is the average length of time for a transaction block to be hashed. However, some more sensitive or larger transactions may require multiple confirmations, meaning that more blocks must be hashed and added to the block chain after the transaction’s block has been hashed. Each time another block is added to the block chain after the transaction’s block, the transaction is confirmed again.
A proposed add-on function for bitcoin that would enable bitcoin users to give them additional attributes. These attributes could be user-defined, enabling you to mark a bitcoin as a share of stock, or a physical asset. This would enable bitcoins to be traded as tokens for other property.
Central Processing Unit – the ‘brain’ of a computer. In the early days, these were used to hash bitcoin transactions, but are now no longer powerful enough. They are still sometimes used to hash transactions for altcoins.
Another name for the input used in a bitcoin’s generation transaction. When a bitcoin is mined, it doesn’t come from another bitcoin user, but is generated as a reward for the miner. That reward is recorded as a transaction, but instead of another user’s bitcoin address, some arbitrary data is used as the input.
Coinbase is also the name of a bitcoin wallet service that also offers payment processing services for merchants and acts as an intermediary for purchasing bitcoins from exchanges.
The age of a coin, defined as the currency amount multiplied by the holding period.
A form of currency based on mathematics alone. Instead of fiat currency, which is printed, cryptocurrency is produced by solving mathematical problems based on cryptography.
The use of mathematics to create codes and ciphers that can be used to conceal information. Used as the basis for the mathematical problems used to verify and secure bitcoin transactions.
A distributed denial of service attack uses large numbers of computers under an attacker’s control to drain the resources of a central target. They often send small amounts of network traffic across the Internet to tie up computing and bandwidth resources at the target, which prevents it from providing services to legitimate users. Bitcoin exchanges have sometimes been hit with DDoS attacks.
The reduction of prices in an economy over time. It happens when the supply of a good or service increases faster than the supply of money, or when the supply of money is finite, and decreases. This leads to more goods or services per unit of currency, meaning that less currency is needed to purchase them. This carries some downsides. When people expect prices to fall, it causes them to stop spending and hoard money, in the hope that their money will go further later. This can depress an economy.
This number determines how difficult it is to hash a new block. It is related to the maximum allowed number in a given numerical portion of a transaction block’s hash. The lower the number, the more difficult it is to produce a hash value that fits it. Difficulty varies based on the amount of computing power used by miners on the bitcoin network. If large numbers of miners leave a network, the difficulty would decrease. Thus far, however, bitcoin’s growing popularity has attracted more computing power to the network, meaning that the difficulty has increased.
The act of spending bitcoins twice. It happens when someone makes a transaction using bitcoins, and then makes a second purchase from someone else, using the same bitcoins. They then convince the rest of the network to confirm only one of the transactions by hashing it in a block. Double spending is not easy to do, thanks to the way that the bitcoin network operates, but it is nevertheless a risk run by those accepting zero-confirmation transactions.
A transaction for an extremely small amount of bitcoins, which offers little financial value, but takes up space in the block chain. The bitcoin developer team has taken efforts to eliminate dust transactions by increasing the minimum transaction amount that will be relayed by the network.
The Elliptic Curve Digital Signature Algorithm is the lightweight cryptographic algorithm used to sign transactions in the Bitcoin protocol.
The act of holding funds or assets in a third-party account to protect them during an asynchronous transaction. If Bob wants to send money to Alice in exchange for a file, but they cannot conduct the exchange in person, then how can they trust each other to send the money and file to each other at the same time? Instead, Bob sends the money to Eve, a trusted party who holds the funds until Bob confirms that he has received the file from Alice. She then sends Alice the money.
A central resource for exchanging different forms of money and other assets. Bitcoin exchanges are typically used to exchange the cryptocurrency for other, typically fiat, currencies.
A technique used when first launching an altcoin. A set number of coins are pre-mined, and given away for free, to encourage people to take interest in the coin and begin mining it themselves.
An altcoin based on the Scrypt proof of work algorithm.
A currency, conjured out of thin air, which only has value because people say it does. Constantly under close scrutiny by regulators due to its known application in money laundering and terrorist activities. Not to be confused with bitcoin.
The Financial Crimes Enforcement Network, an agency within the US Treasury Department. FinCEN has thus far been the main organization to impose regulations on exchanges trading in bitcoin.
The creation of an alternative ongoing version of the block chain, typically because one set of miners begins hashing a different set of transaction blocks from another. It can be caused maliciously, by a group of miners gaining too much control over the network (see 51% attack), accidentally, thanks to a bug in the system, or intentionally, when a core development team decides to introduce substantial new features into a new version of a client. A fork is successful if it becomes the longest version of the block chain, as defined by difficulty.
A Field Programmable Gate Array is a processing chip that can be configured with custom functions after it has been fabricated. Think of it as a blank silicon slate on which instructions can be written. Because FPGAs can be produced en masse and configured after fabrication, manufacturers benefit from economies of scale, making them cheaper than ASIC chips. However, they are usually far slower.
A cryptocurrency based on the inflation-free principles outlined by the economist Silvio Gessell.
The very first block in the block chain.
The number of hashing attempts possible in a given second, measured in billions of hashes (thousands of Megahashes).
Graphical Processing Unit. A silicon chip specifically designed for the complex mathematical calculations needed to render millions of polygons in modern computer game graphics. They are also well suited to the cryptographic calculations needed in cryptocurrency mining.
A mathematical process that takes a variable amount of data and produces a shorter, fixed-length output. A hashing function has two important characteristics. Firstly, it is mathematically difficult to work out what the original input was by looking at the output. Secondly, changing even the tiniest part of the input will produce an entirely different output.
The number of hashes that can be performed by a bitcoin miner in a given period of time (usually a second).
When the value of money drops over time, causing prices for goods to increase. The result is a drop in purchasing power. Effects include less motivation to hoard money, and more motivation to spend it quickly while the prices of goods are still low.
The part of a bitcoin transaction denoting where the bitcoin payment has come from. Typically, this will be a bitcoin address, unless the transaction is a generation transaction, meaning that the bitcoin has been freshly mined (see Coinbase).
The number of hashing attempts possible in a given second, measured in thousands of hashes.
Know Your Client rules force financial institutions to vet the people they are doing business with, ensuring that they are legitimate.
In foreign currency trading, leverage multiplies the real funds in your account by a given factor, enabling you to make trades that result in significant profit. By giving leverage to a trader, the trading exchange is effectively lending them money, in the hope that it will earn back more than it loaned in commission. Leverage is also known as a margin requirement.
A centralized digital currency payment processor based in Costa Rica. It was shut down by the US government, after it was found guilty of money laundering.
An altcoin based on the Scrypt proof of work. Read Litecoin news to find out more.
The ability to buy and sell an asset easily, with pricing that stays roughly similar between trades. A suitably large community of buyers and sellers is important for liquidity. The result of an illiquid market is price volatility, and the inability to easily determine the value of an asset.
The act of calling in a margin requirement. An exchange will issue a margin call when it feels that a trader does not have sufficient funds to cover a leveraged trading position.
The number of hashing attempts possible in a given second, measured in millions of hashes (thousands of Kilohashes).
An instruction given to an exchange, asking it to buy or sell an asset at the going market rate. In a bitcoin exchange, you would place a market order if you simply wanted to buy or sell bitcoins immediately, rather than holding them until a set market condition is triggered to try and make a profit.
1 thousandth of a bitcoin (0.001 BTC).
Paying a tiny amount for an asset or service, primarily online. Micro-transactions are difficult to perform under conventional payment systems, because of the heavy commissions involved. It is difficult to pay two cents to read an online article using your credit card, for example.
The act of generating new bitcoins by solving cryptographic problems using computing hardware.
A service that mixes your bitcoins with someone else’s, sending you back bitcoins with different inputs and outputs from the ones that you sent to it. A mixing service (also known as a tumbler) preserves your privacy because it stops people tracing a particular bitcoin to you. It also has the potential to be used for money laundering.
One of the first bitcoin exchanges, and at one time the most popular. Mt. Gox has since gone into administration. Based in Japan, the exchange was started by Jed McCaleb in 2010. Read the latest Mt. Gox news.
An altcoin designed to provide an alternative to the traditional domain name system (DNS). Users can register .bit domains, accessible via proxy servers, by paying with namecoins.
A computer connected to the bitcoin network using a client that relays transactions to others (see client).
A random string of data used as an input when hashing a transaction block. A nonce is used to try and produce a digest that fits the numerical parameters set by the bitcoin difficulty. A different nonce will be used with each hashing attempt, meaning that billions of nonces are generated when attempting to hash each transaction block.
A block which is not a part of the valid block chain, but which was instead part of a fork that was discarded.
An exchange in which traders make deals with each other directly, rather than relying on a central exchange to mediate between them.
The destination address for a bitcoin transaction. There can be multiple outputs for a single transaction.
Peer-to-peer. Decentralized interactions that happen between at least two parties in a highly interconnected network. An alternative system to a ‘hub-and-spoke’ arrangement, in which all participants in a transaction deal with each other through a single mediation point.
A printed sheet containing one or more public bitcoin addresses and their corresponding private keys. Often used to store bitcoins securely, instead of using software wallets, which can be corrupted, or web wallets, which can be hacked or simply disappear. A useful form of cold bitcoin storage.
A collection of mining clients which collectively mine a block, and then split the reward between them. Mining pools are a useful way to increase your probability of successfully mining a block as the difficulty rises.
AKA Peercoin or P2P coin. An altcoin using the proof of stake mechanism in conjunction with proof of work. Based on a paper produced by Sunny King and Scott Nadal.
The mining of coins by a cryptocurrency’s founder before that coin has been announced and details released to others who may wish to mine the coin. Pre-mining is a common technique used with scamcoins, although not all pre-mined coins are scamcoins (see Scamcoins).
Developed by Sunny King, Primecoin uses a proof of work system to calculate prime numbers.
An alphanumeric string kept secret by the user, and designed to sign a digital communication when hashed with a public key. In the case of bitcoin, this string is a private key designed to work with a public key. The public key is a bitcoin address (see Bitcoin address).
Payment Service Provider. The PSP offers payment processing services for merchants who wish to accept payments online.
Pump and dump
Inflating the value of a financial asset that has been produced or acquired cheaply, using aggressive publicity and often misleading statements. The publicity causes others to acquire the asset, forcing up its value. When the value is high enough, the perpetrator sells their assets, cashing in and flooding the market, which causes the value to crash.
The size of a transistor in nanometers, produced during a chip fabrication process. Smaller process nodes are more efficient.
Proof of stake
An alternative to proof of work, in which your existing stake in a currency (the amount of that currency that you hold) is used to calculate the amount of that currency that you can mine.
Proof of work
A system that ties mining capability to computational power. Blocks must be hashed, which is in itself an easy computational process, but an additional variable is added to the hashing process to make it more difficult. When a block is successfully hashed, the hashing must have taken some time and computational effort. Thus, a hashed block is considered proof of work.
An alphanumeric string which is publicly known, and which is hashed with another, privately held string to sign a digital communication. In the case of bitcoin, the public key is a bitcoin address.
A two-dimensional graphical block containing a monochromatic pattern representing a sequence of data. QR codes are designed to be scanned by cameras, including those found in mobile phones, and are frequently used to encode bitcoin addresses.
A payment network that can be used to transfer any currency (including ad hoc currencies that have been created by users). The network consists of payment nodes and gateways operated by authorities. Payments are made using a series of IOUs, and the network is based on trust relationships.
The smallest subdivision of a bitcoin currently available (0.00000001 BTC).
The name used by the original inventor of the Bitcoin protocol, who withdrew from the project at the end of 2010.
An altcoin produced with the sole purpose of making money for the originator. Scamcoins frequently use pump and dump techniques and pre-mining together.
An alternative proof of work system to SHA-256, designed to be particularly friendly to CPU and GPU miners, while offering little advantage to ASIC miners.
A digital digest produced by hashing private and public keys together to prove that a bitcoin transaction came from a particular address.
An underground online marketplace, generally used for illicit purchases, often with cryptocurrencies such as bitcoin. Silk Road was shut down in early October 2013 by the FBI after owner Ross Ulbricht was arrested.
The Single European Payments Area. A payment integration agreement within the European Union, designed to make it easier to transfer funds between different banks and nations in euros.
The cryptographic function used as the basis for bitcoin’s proof of work system.
Simplified Payment Verification. A feature of the Bitcoin protocol that enables nodes to verify payments without downloading the full block chain. Instead, they need only download block headers.
When a bitcoin block is successfully hashed, any others attempting to hash it may as well stop, because it is now ‘stale’. They would simply be repeating work that someone else has already done, for no reward. The term is also used in mining pools to describe a share of a hashing job that has already been completed.
An analysis of how closely related two addresses are when they have both held a particular bitcoin. A taint analysis could be used to determine how many steps it took for bitcoins to move from an address known for stolen coins, to the current address.
The number of hashing attempts possible in a given second, measured in trillions of hashes (thousands of Gigahashes).
An alternative bitcoin block chain, used purely for testing purposes.
An anonymous routing protocol, used by people wanting to hide their identity online.
A collection of transactions on the bitcoin network, gathered into a block that can then be hashed and added to the block chain.
A small fee imposed on some transactions sent across the bitcoin network. The transaction fee is awarded to the miner that successfully hashes the block containing the relevant transaction.
One microbitcoin (0.000001 BTC)
A bitcoin address with a desirable pattern, such as a name.
Bitcoins purchased as a reward for mining a block. These have not yet been spent anywhere.
The measurement of price movements over time for a traded financial asset (including bitcoin).
Another altcoin, www.w2coin.org
A method of storing bitcoins for later use. A wallet holds the private keys associated with bitcoin addresses. The block chain is the record of the bitcoin amounts associated with those addresses.
Electronically transferring money from one person to another. Commonly used to send and retrieve fiat currency from bitcoin exchanges.
A protocol designed to make cryptocurrency transactions truly anonymous.
A transaction in which the merchant is happy to provide a product or service before the bitcoin’s transmission has been confirmed by a miner and added to the block chain. It can carry a risk of double spending.