In the blockchain, bitcoins are registered to bitcoin addresses. Creating a bitcoin address requires nothing more than picking a random valid private key and computing the corresponding bitcoin address. This computation can be done in a split second. But the reverse, computing the private key of a given bitcoin address, is mathematically unfeasible. Users can tell others or make public a bitcoin address without compromising its corresponding private key. Moreover, the number of valid private keys is so vast that it is extremely unlikely someone will compute a key-pair that is already in use and has funds. The vast number of valid private keys makes it unfeasible that brute force could be used to compromise a private key. To be able to spend their bitcoins, the owner must know the corresponding private key and digitally sign the transaction. The network verifies the signature using the public key.[3]:ch. 5
Bitcoin is a type of cryptocurrency: Balances are kept using public and private "keys," which are long strings of numbers and letters linked through the mathematical encryption algorithm that was used to create them. The public key (comparable to a bank account number) serves as the address which is published to the world and to which others may send bitcoins. The private key (comparable to an ATM PIN) is meant to be a guarded secret, and only used to authorize Bitcoin transmissions.
On 1 August 2017, a hard fork of bitcoin was created, known as Bitcoin Cash.[103] Bitcoin Cash has a larger block size limit and had an identical blockchain at the time of fork. On 24 October 2017 another hard fork, Bitcoin Gold, was created. Bitcoin Gold changes the proof-of-work algorithm used in mining, as the developers felt that mining had become too specialized.[104]

We will look at bitcoin as currency and bitcoin as a store of value.  In order to place a value on bitcoin we need to project what market penetration it will achieve in each sphere.  This article will not make a case for what the market penetration will be, but for the sake of the evaluation, we'll pick a rather arbitrary value of 15%, both for bitcoin as a currency and bitcoin as a store of value.  You are encouraged to form your own opinion for this projection and adjust the valuation accordingly.
Speculation drives numbers. Many Bitcoin users are holding onto their bitcoins in hopes of selling them off for an enormous profit one day. With news articles portraying Bitcoin millionaires as lucky kids who got in early, you can’t really blame them. For example, if you had spent your \$5 latte money on 2,000 bitcoins one morning in 2010, they would be worth about \$5.4 million today. Makes you really wish you’d managed your Starbucks budget better, doesn’t it?
The overwhelming majority of bitcoin transactions take place on a cryptocurrency exchange, rather than being used in transactions with merchants.[133] Delays processing payments through the blockchain of about ten minutes make bitcoin use very difficult in a retail setting. Prices are not usually quoted in units of bitcoin and many trades involve one, or sometimes two, conversions into conventional currencies.[30] Merchants that do accept bitcoin payments may use payment service providers to perform the conversions.[134]

The price of bitcoins has gone through cycles of appreciation and depreciation referred to by some as bubbles and busts.[155] In 2011, the value of one bitcoin rapidly rose from about US\$0.30 to US\$32 before returning to US\$2.[156] In the latter half of 2012 and during the 2012–13 Cypriot financial crisis, the bitcoin price began to rise,[157] reaching a high of US\$266 on 10 April 2013, before crashing to around US\$50.[158] On 29 November 2013, the cost of one bitcoin rose to a peak of US\$1,242.[159] In 2014, the price fell sharply, and as of April remained depressed at little more than half 2013 prices. As of August 2014 it was under US\$600.[160] During their time as bitcoin developers, Gavin Andresen[161] and Mike Hearn[162] warned that bubbles may occur.
###### Bitcoin has become more widely traded as of 2017, and both short term traders and long-term investors are looking to participate in this exciting market. The price of bitcoin fluctuates on a daily basis, and can see some significant price volatility. Prices can be affected by numerous influences. Some of the possible drivers of price include: further acceptance, more exchanges opening, regulations, weakening paper currency values, inflation and more.

Speculation drives numbers. Many Bitcoin users are holding onto their bitcoins in hopes of selling them off for an enormous profit one day. With news articles portraying Bitcoin millionaires as lucky kids who got in early, you can’t really blame them. For example, if you had spent your \$5 latte money on 2,000 bitcoins one morning in 2010, they would be worth about \$5.4 million today. Makes you really wish you’d managed your Starbucks budget better, doesn’t it?