Bitcoin, along with other cryptocurrencies, has been described as an economic bubble by at least eight Nobel Memorial Prize in Economic Sciences laureates, including Robert Shiller,[144] Joseph Stiglitz,[202] and Richard Thaler.[203][204] Noted Keynesian economist Paul Krugman has described bitcoin as "a bubble wrapped in techno-mysticism inside a cocoon of libertarian ideology",[135] professor Nouriel Roubini of New York University has called bitcoin the "mother of all bubbles",[205] and University of Chicago economist James Heckman has compared it to the 17th-century tulip mania.[204] Former Federal Reserve Chairman Alan Greenspan has also described bitcoin as a "bubble";[206] the investors Warren Buffett and George Soros have respectively characterized it as a "mirage"[207] and a "bubble";[208] while the business executives Jack Ma and Jamie Dimon have called it a "bubble"[209] and a "fraud",[210] respectively.
Using Ethereum’s “Turing complete” smart contract language, Solidity, developers are able to deploy a set of instructions to the blockchain that operate indefinitely with a high degree of finality and fraud-resistance. With the first block being mined in July 2015, Ethereum has since become the largest smart contract platform of its kind, and the second largest blockchain of all time as measured by market capitalization.
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Then, in early 2009, an anonymous programmer or a group of programmers under an alias Satoshi Nakamoto introduced Bitcoin. Satoshi described it as a ‘peer-to-peer electronic cash system.’ It is completely decentralized, meaning there are no servers involved and no central controlling authority. The concept closely resembles peer-to-peer networks for file sharing.
J. P. Morgan Chase is developing JPM Coin on a permissioned-variant of Ethereum blockchain dubbed "Quorum".[52] It's designed to toe the line between private and public in the realm of shuffling derivatives and payments. The idea is to satisfy regulators who need seamless access to financial goings-on, while protecting the privacy of parties that don't wish to reveal their identities nor the details of their transactions to the general public.[53]

Ethereum addresses are composed of the prefix "0x", a common identifier for hexadecimal, concatenated with the rightmost 20 bytes of the Keccak-256 hash (big endian) of the ECDSA public key (the curve used is the so called secp256k1, the same as Bitcoin). In hexadecimal, 2 digits represents a byte, meaning addresses contain 40 hexadecimal digits. An example of an Ethereum address is 0xb794F5eA0ba39494cE839613fffBA74279579268. Contract addresses are in the same format, however they are determined by sender and creation transaction nonce.[34] User accounts are indistinguishable from contract accounts given only an address for each and no blockchain data. Any valid Keccak-256 hash put into the described format is valid, even if it does not correspond to an account with a private key or a contract. This is unlike Bitcoin, which uses base58check to ensure that addresses are properly typed.
2) Pseudonymous: Neither transactions nor accounts are connected to real-world identities. You receive Bitcoins on so-called addresses, which are randomly seeming chains of around 30 characters. While it is usually possible to analyze the transaction flow, it is not necessarily possible to connect the real world identity of users with those addresses.
Then, in early 2009, an anonymous programmer or a group of programmers under an alias Satoshi Nakamoto introduced Bitcoin. Satoshi described it as a ‘peer-to-peer electronic cash system.’ It is completely decentralized, meaning there are no servers involved and no central controlling authority. The concept closely resembles peer-to-peer networks for file sharing.
Lightweight clients consult full clients to send and receive transactions without requiring a local copy of the entire blockchain (see simplified payment verification – SPV). This makes lightweight clients much faster to set up and allows them to be used on low-power, low-bandwidth devices such as smartphones. When using a lightweight wallet, however, the user must trust the server to a certain degree, as it can report faulty values back to the user. Lightweight clients follow the longest blockchain and do not ensure it is valid, requiring trust in miners.[101]
Network nodes can validate transactions, add them to their copy of the ledger, and then broadcast these ledger additions to other nodes. To achieve independent verification of the chain of ownership each network node stores its own copy of the blockchain.[80] About every 10 minutes, a new group of accepted transactions, called a block, is created, added to the blockchain, and quickly published to all nodes, without requiring central oversight. This allows bitcoin software to determine when a particular bitcoin was spent, which is needed to prevent double-spending. A conventional ledger records the transfers of actual bills or promissory notes that exist apart from it, but the blockchain is the only place that bitcoins can be said to exist in the form of unspent outputs of transactions.[7]:ch. 5
To understand the revolutionary impact of cryptocurrencies you need to consider both properties. Bitcoin as a permissionless, irreversible, and pseudonymous means of payment is an attack on the control of banks and governments over the monetary transactions of their citizens. You can‘t hinder someone to use Bitcoin, you can‘t prohibit someone to accept a payment, you can‘t undo a transaction.
It takes a (global) village to raise a blockchain. The live network and the community of open source developers contribute significantly to this effort. They continuously refine and harden the Ethereum platform, helping it get faster at responding to industry demands for the value propositions it offers. These investments of time and resources speak to their faith in Ethereum governance and the value that businesses and developers see in its capabilities. – Joseph Lubin, CEO of Consensys

While cryptocurrencies are digital currencies that are managed through advanced encryption techniques, many governments have taken a cautious approach toward them, fearing their lack of central control and the effects they could have on financial security.[81] Regulators in several countries have warned against cryptocurrency and some have taken concrete regulatory measures to dissuade users.[82] Additionally, many banks do not offer services for cryptocurrencies and can refuse to offer services to virtual-currency companies.[83] Gareth Murphy, a senior central banking officer has stated "widespread use [of cryptocurrency] would also make it more difficult for statistical agencies to gather data on economic activity, which are used by governments to steer the economy". He cautioned that virtual currencies pose a new challenge to central banks' control over the important functions of monetary and exchange rate policy.[84] While traditional financial products have strong consumer protections in place, there is no intermediary with the power to limit consumer losses if bitcoins are lost or stolen.[85] One of the features cryptocurrency lacks in comparison to credit cards, for example, is consumer protection against fraud, such as chargebacks.


In the end, the majority of the Ethereum community voted to perform a hard fork, and retrieve The DAO investors money. But not everyone agreed with this course of action. This resulted in a split where two parallel blockchains now exist. For those members who strongly disagree with any changes to the blockchain even when hacking occurs there is Ethereum classic. For the majority who agreed to rewrite a small part of the blockchain and return the stolen money to their owners, there is Ethereum.  
Izabella Kaminska, the editor of FT Alphaville, has pointed out that criminals are using Ethereum to run Ponzi schemes and other forms of investment fraud.[68] The article was based on a paper from the University of Cagliari, which placed the number of Ethereum smart contracts which facilitate Ponzi schemes at nearly 10% of 1384 smart contracts examined. However, it also estimated that only 0.05% of the transactions on the network were related to such contracts.[69]
Ethereum's smart contracts are based on different computer languages, which developers use to program their own functionalities. Smart contracts are high-level programming abstractions that are compiled down to EVM bytecode and deployed to the Ethereum blockchain for execution. They can be written in Solidity (a language library with similarities to C and JavaScript), Serpent (similar to Python, but deprecated), LLL (a low-level Lisp-like language), and Mutan (Go-based, but deprecated). There is also a research-oriented language under development called Vyper (a strongly-typed Python-derived decidable language).
Once you bought your cryptocurrency, you need a way to store it. All major exchanges offer wallet services. But, while it might seem convenient, it’s best if you store your assets in an offline wallet on your hard drive, or even invest in a hardware wallet. This is the most secure way of storing your coins and it gives you full control over your assets.
The unit of account of the bitcoin system is a bitcoin. Ticker symbols used to represent bitcoin are BTC[b] and XBT.[c][76]:2 Its Unicode character is ₿.[1] Small amounts of bitcoin used as alternative units are millibitcoin (mBTC), and satoshi (sat). Named in homage to bitcoin's creator, a satoshi is the smallest amount within bitcoin representing 0.00000001 bitcoins, one hundred millionth of a bitcoin.[2] A millibitcoin equals 0.001 bitcoins; one thousandth of a bitcoin or 100,000 satoshis.[77]
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