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Artur Virgílio Alves Reis (Lisbon, 8 September 1896 – 9 June 1955) was a Portuguese criminal who perpetrated one of the largest frauds in history, against the Bank of Portugal in 1925, often called the Portuguese Bank Note Crisis.

Base58 is a group of binary-to-text encoding schemes used to represent large integers as alphanumeric text, introduced by Satoshi Nakamoto for use with Bitcoin. It has since been applied to other cryptocurrencies and applications. It is similar to Base64 but has been modified to avoid both non-alphanumeric characters and letters which might look ambiguous when printed. It is therefore designed for human users who manually enter the data, copying from some visual source, but also allows easy copy and paste because a double-click will usually select the whole string.

Compared with Base64, the following similar-looking letters are omitted: 0 (zero), O (capital o), I (capital i) and l (lower case L) as well as the non-alphanumeric characters + (plus) and / (slash). In contrast with Base64, the digits of the encoding do not line up well with byte boundaries of the original data. For this reason, the method is well-suited to encode large integers, but not designed to encode longer portions of binary data. The actual order of letters in the alphabet depends on the application, which is the reason why the term “Base58” alone is not enough to fully describe the format. A variant, Base56, excludes 1 (one) and o (lowercase o) compared with Base 58.

Base58Check is a Base58 encoding format that unambiguously encodes the type of data in the first few characters and includes an error detection code in the last few characters.

BerkShares is a local currency that circulates in The Berkshires region of Massachusetts. It was launched on September 29, 2006 by BerkShares Inc., with research and development assistance from the Schumacher Center for a New Economics. The BerkShares website lists around 400 businesses in Berkshire County that accept the currency. Since launch, over 10 million BerkShares have been issued from participating branch offices of local banks (as of February 2020, 9 branches of 3 different banks). The bills were designed by John Isaacs and were printed by Excelsior Printing on special paper with incorporated security features from Crane & Co.. BerkShares are pegged with an exchange rate to the US dollar, but the Schumacher Center has discussed the possibility of pegging its value to a basket of local goods in order to insulate the local economy against volatility in the US economy.

Bitcoin (₿) is a cryptocurrency. It is a decentralized digital currency without a central bank or single administrator that can be sent from user to user on the peer-to-peer bitcoin network without the need for intermediaries.

Transactions are verified by network nodes through cryptography and recorded in a public distributed ledger called a blockchain. Bitcoin was invented in 2008 by an unknown person or group of people using the name Satoshi Nakamoto and started in 2009 when its source code was released as open-source software. Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies, products, and services. Research produced by University of Cambridge estimates that in 2017, there were 2.9 to 5.8 million unique users using a cryptocurrency wallet, most of them using bitcoin.

Bitcoin has been criticized for its use in illegal transactions, its high electricity consumption, price volatility, and thefts from exchanges. Some economists, including several Nobel laureates, have characterized it as a speculative bubble. Bitcoin has also been used as an investment, although several regulatory agencies have issued investor alerts about bitcoin.

Dogecoin ( DOHJ-koyn, code: DOGE, symbol: Ð) is a cryptocurrency featuring a likeness of the Shiba Inu dog from the "Doge" Internet meme as its logo. Introduced as a "joke currency" on 6 December 2013, Dogecoin quickly developed its own online community and reached a capitalization of US$60 million in January 2014.

Compared with other cryptocurrencies, Dogecoin had a fast initial coin production schedule: 100 billion coins were in circulation by mid-2015, with an additional 5.256 billion coins every year thereafter. As of 30 June 2015, the 100 billionth Dogecoin had been mined. While there are few mainstream commercial applications, the currency has gained traction as an Internet tipping system, in which social media users grant Dogecoin tips to other users for providing interesting or noteworthy content. Dogecoin is referred to as an altcoin.

The EURion constellation (also known as Omron rings or doughnuts) is a pattern of symbols incorporated into a number of banknote designs worldwide since about 1996. It is added to help imaging software detect the presence of a banknote in a digital image. Such software can then block the user from reproducing banknotes to prevent counterfeiting using colour photocopiers. According to research from 2004, the EURion constellation is used for colour photocopiers but probably not used in computer software. It has been reported that Adobe Photoshop will not allow editing of an image of a banknote, but in some versions this is believed to be due to a different, unknown digital watermark rather than the EURion constellation.

In economics, Gresham's law is a monetary principle stating that "bad money drives out good". For example, if there are two forms of commodity money in circulation, which are accepted by law as having similar face value, the more valuable commodity will gradually disappear from circulation.

The law was named in 1860 by Henry Dunning Macleod, after Sir Thomas Gresham (1519–1579), who was an English financier during the Tudor dynasty. However, the concept itself had been previously expressed by others, including by Aristophanes in his play The Frogs, which dates from around the end of the 5th century BC, in the 14th century by Nicole Oresme c. 1350, in his treatise On the Origin, Nature, Law, and Alterations of Money, and by jurist and historian Al-Maqrizi (1364–1442) in the Mamluk Empire; and in 1519 by Nicolaus Copernicus in a treatise called Monetae cudendae ratio For this reason, it is occasionally known as the Gresham–Copernicus' law.

The Indian rupee sign (sign: ₹; code: INR) is the currency symbol for the Indian rupee, the official currency of India. Designed by Udaya Kumar, it was presented to the public by the Government of India on 15 July 2010, following its selection through an "open" competition among Indian residents. Before its adoption, the most commonly used symbols for the rupee were Rs, Re or, in texts in Indian languages, an appropriate abbreviation in the language used.

The design is based on the Devanagari letter "र" (ra) with a double horizontal line at the top. It also resembles the Latin capital letter "R", especially R rotunda (Ꝛ).

The Unicode character for the Indian rupee sign is U+20B9 ₹ INDIAN RUPEE SIGN. Other countries that use a rupee, such as Sri Lanka, Pakistan and Nepal, still use the generic U+20A8 ₨ RUPEE SIGN character.

Mt. Gox was a bitcoin exchange based in Shibuya, Tokyo, Japan. Launched in July 2010, by 2013 and into 2014 it was handling over 70% of all bitcoin (BTC) transactions worldwide, as the largest bitcoin intermediary and the world's leading bitcoin exchange.

In February 2014, Mt. Gox suspended trading, closed its website and exchange service, and filed for bankruptcy protection from creditors. In April 2014, the company began liquidation proceedings.

Mt. Gox announced that approximately 850,000 bitcoins belonging to customers and the company were missing and likely stolen, an amount valued at more than $450 million at the time. Although 200,000 bitcoins have since been "found", the reasons for the disappearance—theft, fraud, mismanagement, or a combination of these—were initially unclear. New evidence presented in April 2015 by Tokyo security company WizSec led them to conclude that "most or all of the missing bitcoins were stolen straight out of the Mt. Gox hot wallet over time, beginning in late 2011."

Namecoin (Symbol: ℕ or NMC) is a cryptocurrency originally forked from bitcoin software. It is based on the code of bitcoin and uses the same proof-of-work algorithm. Like bitcoin, it is limited to 21 million coins.

Namecoin can store data within its own blockchain transaction database. The original proposal for Namecoin called for Namecoin to insert data into bitcoin's blockchain directly. Anticipating scaling difficulties with this approach, a shared proof-of-work (POW) system was proposed to secure new cryptocurrencies with different use cases.

Namecoin's flagship use case is the censorship-resistant top level domain .bit, which is functionally similar to .com or .net domains but is independent of ICANN, the main governing body for domain names.