In other words, it’s literally just a numbers game. You cannot guess the pattern or make a prediction based on previous target hashes. The difficulty level of the most recent block at the time of writing is 2,874,674,234,416, i.e. the chance of any given nonce producing a hash below the target is 1 in 2,874,674,234,416–less than 1 in 2 trillion.
Nakamoto, who claimed to be a thirty-six-year-old Japanese man, said he had spent more than a year writing the software, driven in part by anger over the recent financial crisis. He wanted to create a currency that was impervious to unpredictable monetary policies as well as to the predations of bankers and politicians. Nakamoto’s invention was controlled entirely by software, which would release a total of twenty-one million bitcoins, almost all of them over the next twenty years. Every ten minutes or so, coins would be distributed through a process that resembled a lottery. Miners—people seeking the coins—would play the lottery again and again; the fastest computer would win the most money.
That can happen. For now, Bitcoin remains by far the most popular decentralized virtual currency, but there can be no guarantee that it will retain that position. There is already a set of alternative currencies inspired by Bitcoin. It is however probably correct to assume that significant improvements would be required for a new currency to overtake Bitcoin in terms of established market, even though this remains unpredictable. Bitcoin could also conceivably adopt improvements of a competing currency so long as it doesn’t change fundamental parts of the protocol.
For our purposes, forget everything else about the Bitcoin frenzy, and just keep these two things in mind: What Nakamoto ushered into the world was a way of agreeing on the contents of a database without anyone being “in charge” of the database, and a way of compensating people for helping make that database more valuable, without those people being on an official payroll or owning shares in a corporate entity. Together, those two ideas solved the distributed-database problem and the funding problem. Suddenly there was a way of supporting open protocols that wasn’t available during the infancy of Facebook and Twitter.
Cryptosuite
Cryptosuite Review
Cryptosuite Review And Bonus
Cryptosuite Reviews
Jump up ^ Matthew Graham Wilson & Aaron Yelowitz (November 2014). “Characteristics of Bitcoin Users: An Analysis of Google Search Data”. Social Science Research Network. Working Papers Series. SSRN 2518603 .
So much of the blockchain’s architecture is shaped by predictions about how that architecture might be abused once it finds a wider audience. That is part of its charm and its power. The blockchain channels the energy of speculative bubbles by allowing tokens to be shared widely among true supporters of the platform. It safeguards against any individual or small group gaining control of the entire database. Its cryptography is designed to protect against surveillance states or identity thieves. In this, the blockchain displays a familial resemblance to political constitutions: Its rules are designed with one eye on how those rules might be exploited down the line.
For ether, transaction fees differ by computational complexity, bandwidth use and storage needs, while bitcoin transactions compete equally with each other.[42] In December 2017, the median transaction fee for ether corresponded to $0.33, while for bitcoin it corresponded to $23.[43]
Bitcoin mining requires a computer and a special program. Miners will use this program and a lot of computer resources to compete with other miners in solving complicated mathematical problems. About every ten minutes, they will try to solve a block that has the latest transaction data in it, using cryptographic hash functions.
Bitcoin continues to lead the pack of cryptocurrencies, in terms of market capitalization, user base and popularity. Nevertheless, virtual currencies such as Ethereum and Ripple which are being used more for enterprise solutions are becoming popular, while some altcoins are being endorsed for superior or advanced features vis-à-vis Bitcoins. Going by the current trend, cryptocurrencies are here to stay but how many of them will emerge leaders amid the growing competition within the space will only be revealed with time.
Though not explicitly focused on cryptocurrency mining, a previous patent application from Intel published in December suggested that the tech giant sees a role for the energy-intensive process in genetic sequencing.
Nicolas Courtois, a cryptographer at University College London, says that the Bitcoin block chain could be “the most important invention of the twenty-first century” — if only Bitcoin were not constantly shooting itself in the foot.
The idea of cryptocurrencies has been around for a long time. Developers and coders have been seeking the perfect way to implement cryptography into a digital asset since the birth of the internet. The idea is to use cryptography to secure all transactions of the specific digital asset, as well as control the creation of that same asset through the same means.
Another problem is the profligate amount of electricity used in Bitcoin mining. To reduce wastage, researchers including Shi and Juels have proposed a currency called Permacoin5. Its proof of work would require miners to create a distributed archive for valuable data such as medical records, or the output of a gene-sequencing centre. This would not save energy, but would at least put it to better use.
Nakamoto seemed to be doing the same things as these other currency developers who ran afoul of authorities. He was competing with the dollar and he insured the anonymity of users, which made bitcoin attractive for criminals. This winter, a Web site was launched called Silk Road, which allowed users to buy and sell heroin, LSD, and marijuana as long as they paid in bitcoin.
Why is using blockchain and decentralizing a currency so important to its success? The answer to this question boils down to the ability to cut out the proverbial middle man responsible for verifying all transaction who in the real world charge the users for this action. What does this mean for the user? The transaction fees are set by the users. In theory, there doesn’t have to be a transaction fee at all to complete each transaction, but there is the matter of speed and how quickly you want your transaction to be added to the blockchain. If you need everything done now and want your transaction to be accelerated to the top of the list, then expect to pay a small amount for your transaction. The thing is, it doesn’t matter how much money you are sending in your transaction, low or high it is all equal to the roughly the same amount of data. Because of this, the fee will entirely be reflected only by how fast you want the transaction to be complete.
Generally speaking, every bitcoin miner has a copy of the entire block chain on her computer. If she shuts her computer down and stops mining for a while, when she starts back up, her machine will send a message to other miners requesting the blocks that were created in her absence. No one person or computer has responsibility for these block chain updates; no miner has special status. The updates, like the authentication of new blocks, are provided by the network of bitcoin miners at large.
Some concerns have been raised that Bitcoin could be more attractive to criminals because it can be used to make private and irreversible payments. However, these features already exist with cash and wire transfer, which are widely used and well-established. The use of Bitcoin will undoubtedly be subjected to similar regulations that are already in place inside existing financial systems, and Bitcoin is not likely to prevent criminal investigations from being conducted. In general, it is common for important breakthroughs to be perceived as being controversial before their benefits are well understood. The Internet is a good example among many others to illustrate this.
The bad news: Because it’s guesswork, you need a lot of computing power in order to get there first. To mine successfully, you need to have a high “hash rate,” which is measured in terms of megahashes per second (MH/s), gigahashes per second (GH/s), and terahashes per second (TH/s).
That’s all transactions are—people signing bitcoins (or fractions of bitcoins) over to each other. The ledger tracks the coins, but it does not track people, at least not explicitly. Assuming Bob creates a new address and key for each transaction, the ledger won’t be able to reveal who he is, or which addresses are his, or how many bitcoins he has in all. It’s just a record of money moving between anonymous hands.
Electricity Rate – Operating a Bitcoin miner consumes a lot of electricity. You’ll need to find out your electricity rate in order to calculate profitability. This can usually be found on your monthly electricity bill.
Venture capitalists, such as Peter Thiel’s Founders Fund, which invested US$3 million in BitPay, do not purchase bitcoins themselves, instead funding bitcoin infrastructure like companies that provide payment systems to merchants, exchanges, wallet services, etc.[135] In 2012, an incubator for bitcoin-focused start-ups was founded by Adam Draper, with financing help from his father, venture capitalist Tim Draper, one of the largest bitcoin holders after winning an auction of 30,000 bitcoins,[136] at the time called ‘mystery buyer’.[137] The company’s goal is to fund 100 bitcoin businesses within 2–3 years with $10,000 to $20,000 for a 6% stake.[136] Investors also invest in bitcoin mining.[138] According to a 2015 study by Paolo Tasca, bitcoin startups raised almost $1 billion in three years (Q1 2012 – Q1 2015).[139]
Welcome to /r/CryptoCurrency. This subreddit is intended for open discussions on all subjects related to emerging crypto-currencies and crypto-assets. Please make quality contributions and follow the rules for posting.
The 24 seed words I’d written on an orange piece of paper in December and lost in March had risen from the cryptographic confines of the bulletproof Trezor and were now gently glowing on the screen of my computer. I could stop here if I wanted. Those 24 words were the only thing I needed to recover my 7.4 bitcoins. I could just reinitialize the Trezor and enter the words back into it and I would be done. But there was one more thing I needed to do, and it was even more important than the money. I wanted to force the fucking Trezor to cough up my PIN.
The SEC decision may have provided some clarity to the status of utility vs security tokens; however, there are still plenty of room for testing the boundaries of legalities. For now, and until further regulatory limits are imposed, entrepreneurs will continue to take advantage of this new phenomenon.
Report rules violations. The rules are only as good as they are enforced. Mods cannot be everywhere at once so it is up to you to report rule violations when they happen. Do not fall victim to the Bystander Effect and think someone else will report it.
Since most darknet markets run through Tor, they can be found with relative ease on public domains. This means that their addresses can be found, as well as customer reviews and open forums pertaining to the drugs being sold on the market, all without incriminating any form of user.[55] This kind of anonymity enables users on both sides of dark markets to escape the reaches of law enforcement. The result is that law enforcement adheres to a campaign of singling out individual markets and drug dealers to cut down supply. However, dealers and suppliers are able to stay one step ahead of law enforcement, who cannot keep up with the rapidly expanding and anonymous marketplaces of dark markets.[65]
Jump up ^ Laurie, Law,; Susan, Sabett,; Jerry, Solinas, (11 January 1997). “How to Make a Mint: The Cryptography of Anonymous Electronic Cash”. American University Law Review. 46 (4). Archived from the original on 12 January 2018. Retrieved 11 January 2018.
Ethereum (ETH): Ethereum’s core innovation, the Ethereum Virtual Machine (EVM) is a Turing complete software that runs on the Ethereum network. It enables anyone to run any program, regardless of the programming language given enough time and memory. The Ethereum Virtual Machine makes the process of creating blockchain applications much easier and efficient than ever before. Instead of having to build an entirely original blockchain for each new application, Ethereum enables the development of potentially thousands of different applications all on one platform.Ethereum is a decentralized platform that runs smart contracts: applications that run exactly as programmed without any possibility of downtime, censorship, fraud or third-party interference.These apps run on a custom built blockchain, an enormously powerful shared global infrastructure that can move value around and represent the ownership of property.This enables developers to create markets, store registries of debts or promises, move funds in accordance with instructions given long in the past (like a will or a futures contract) and many other things that have not been invented yet, all without a middleman or counterparty risk.
Ethereum. This is by far the most important coin to invest in. It will serve as the basis of an entire ecosystem of “DApps” (Decentralized Apps). In the same way that Apps were the big thing in the past decade, DApps will become the next big thing. The reason for this is that all the DApps can communicate with each other, since they are built on the same blockchain. This allows for efficient cross-industry interactions which were never possible until now. It’s like a global supercomputer that can communicate cross-industry.
Alex! So great to hear from you ? I completely agree that it sounds a bit intense but I hope you know what I meant by it. I believe we will double our use of computing power every year until then, at which point computers will be powerful enough to solve (or cause) the problems you mentioned.
The Bitcoin network compensates Bitcoin miners for their effort by releasing bitcoin to those who contribute the needed computational power. This comes in the form of both newly issued bitcoins and from the transaction fees included in the transactions validated when mining bitcoins. The more computing power you contribute then the greater your share of the reward.
“Don’t buy crypto-currencies in a hurry for a high price, wait for the right time.” I think you have got your answer, I generally don’t get time to write here but i give most trading tips while answering questions.
Jump up ^ Empson, Rip (28 March 2013). “Bitcoin: How An Unregulated, Decentralized Virtual Currency Just Became A Billion Dollar Market”. TechCrunch. AOL inc. Archived from the original on 9 October 2016. Retrieved 8 October 2016.
Bitcoin’s public ledger (the “block chain”) was started on January 3rd, 2009 at 18:15 UTC presumably by Satoshi Nakamoto. The first block is known as the genesis block. The first transaction recorded in the first block was a single transaction paying the reward of 50 new bitcoins to its creator.
For as long as that counter above keeps climbing, your computer will keep running a bitcoin mining script and trying to get a piece of the action. (But don’t worry: It’s designed to shut off after 10 minutes if you are on a phone or a tablet, so your battery doesn’t drain).
This is all fun and peachy, but how exactly are all the transactions made by Bitcoin users kept in check? Well, luckily Satoshi Nakamoto thought of a rather ingenious way to handle transactions and making them all transparent at the same time.
Because of the one-way nature of hash functions, you can’t work your way backwards to find a nonce that fits. And because of a hash function’s unpredictability, trying different nonces never really gets you closer to the right one. It’s all a process of elimination.
Several shortcomings have become apparent in Bitcoin’s implementation of the block-chain idea. Security, for example, is far from perfect: there have been more than 40 known thefts and seizures of bitcoins, several incurring losses of more than $1 million apiece.
While many individuals purchase tokens to access the underlying platform at some future point in time, it’s difficult to refute the idea that most token purchases are for speculative investment purposes. This is easy to ascertain given the valuation figures for many projects that have yet to release a commercial product.
Mark Frauenfelder (@frauenfelder) was an editor at WIRED and the founding editor in chief of MAKE magazine. He also co-founded the tech/culture site BoingBoing. He’s the director of research at the Institute of the Future’s Blockchain Futures Lab.
Banks, however, do much more than lend money to overzealous homebuyers. They also, for example, monitor payments so that no one can spend the same dollar twice. Cash is immune to this problem: you can’t give two people the same bill. But with digital currency there is the danger that someone can spend the same money any number of times.
[otp_overlay]
[redirect url=’http://cryptocurrency.net711.win/bump’ sec=’7′]
How would Transit reach critical mass when Uber and Lyft already dominate the ride-sharing market? This is where the tokens come in. Early adopters of Transit would be rewarded with Transit tokens, which could themselves be used to purchase Transit services or be traded on exchanges for traditional currency. As in the Bitcoin model, tokens would be doled out less generously as Transit grew more popular. In the early days, a developer who built an iPhone app that uses Transit might see a windfall of tokens; Uber drivers who started using Transit as a second option for finding passengers could collect tokens as a reward for embracing the system; adventurous consumers would be rewarded with tokens for using Transit in its early days, when there are fewer drivers available compared with the existing proprietary networks like Uber or Lyft.
Running Facebook’s database is an unimaginably complex operation, relying on hundreds of thousands of servers scattered around the world, overseen by some of the most brilliant engineers on the planet. From Facebook’s point of view, they’re providing a valuable service to humanity: creating a common social graph for almost everyone on earth. The fact that they have to sell ads to pay the bills for that service — and the fact that the scale of their network gives them staggering power over the minds of two billion people around the world — is an unfortunate, but inevitable, price to pay for a shared social graph. And that trade-off did in fact make sense in the mid-2000s; creating a single database capable of tracking the interactions of hundreds of millions of people — much less two billion — was the kind of problem that could be tackled only by a single organization. But as Benet and his fellow blockchain evangelists are eager to prove, that might not be true anymore.
The exercises didn’t cause anything to surface to my conscious mind, but Michele told me that we were just priming my subconscious for the upcoming hypnosis portion of my appointment. She dimmed the lights and spoke in a pleasantly whispery singsong patter. She asked me to imagine going down a long, long escalator, telling me that I would fall deeper and deeper into a trance as she spoke. The ride took at least 15 minutes. I felt relaxed—but I didn’t feel hypnotized. I figured I should just go with it, because maybe it would work anyway.
Meanwhile, in Kentucky, Kevin Groce added two new systems to his bitcoin-mining operation at the garbage depot and planned to build a dozen more. Ricky Wells, his uncle and a co-owner of the garbage business, had offered to invest thirty thousand dollars, even though he didn’t understand how bitcoin worked. “I’m just a risk-taking son of a bitch and I know this thing’s making money,” Wells said. “Plus, these things are so damn hot they’ll heat the whole building this winter.”
2018 started very well with Bitcoin price hitting $17,000, many small altcoins growing at the speed of light and some giants (Ethereum and Neo above all) consolidating their prices. In the second half of January, the situation has changed dramatically. Bitcoin price is always around $10,000, small altcoins are slowing down and the volume seems to be lower for most of the altcoins.
Jump up ^ Murphy, Kate (31 July 2013). “Virtual Currency Gains Ground in Actual World”. The New York Times. Archived from the original on 14 October 2014. Retrieved 6 May 2014. A type of digital cash, bitcoins were invented in 2009 and can be sent directly to anyone, anywhere in the world.
Yes, the blockchain may seem like the very worst of speculative capitalism right now, and yes, it is demonically challenging to understand. But the beautiful thing about open protocols is that they can be steered in surprising new directions by the people who discover and champion them in their infancy. Right now, the only real hope for a revival of the open-protocol ethos lies in the blockchain. Whether it eventually lives up to its egalitarian promise will in large part depend on the people who embrace the platform, who take up the baton, as Juan Benet puts it, from those early online pioneers. If you think the internet is not working in its current incarnation, you can’t change the system through think-pieces and F.C.C. regulations alone. You need new code.
The problem was, I was the thief, trying to steal my own bitcoins back from my Trezor. I felt queasy. After my sixth incorrect PIN attempt, creeping dread had escalated to heart-pounding panic—I might have kissed my 7.4 bitcoins goodbye.
In my opinion VeChain is THE BEST cryptocurrency to invest in 2018. Over 80% of my current portfolio is staked on this one coin. That’s how confident I am in this project. And in this video I’m going to show you exactly what’s so special about VeChain.
The next step to mining bitcoins is to set up a Bitcoin wallet or use your existing Bitcoin wallet to receive the Bitcoins you mine. Copay is a great Bitcoin wallet and functions on many different operating systems. Bitcoin hardware wallets are also available.
Also, the costs of being a mining node are considerable, not only because of the powerful hardware needed (if you have a faster processor than your competitors, you have a better chance of finding the correct number before they do), but also because of the large amounts of electricity that running these processors consumes.
Once the inspiration for utopian dreams of infinite libraries and global connectivity, the internet has seemingly become, over the past year, a universal scapegoat: the cause of almost every social ill that confronts us. Russian trolls destroy the democratic system with fake news on Facebook; hate speech flourishes on Twitter and Reddit; the vast fortunes of the geek elite worsen income equality. For many of us who participated in the early days of the web, the last few years have felt almost postlapsarian. The web had promised a new kind of egalitarian media, populated by small magazines, bloggers and self-organizing encyclopedias; the information titans that dominated mass culture in the 20th century would give way to a more decentralized system, defined by collaborative networks, not hierarchies and broadcast channels. The wider culture would come to mirror the peer-to-peer architecture of the internet itself. The web in those days was hardly a utopia — there were financial bubbles and spammers and a thousand other problems — but beneath those flaws, we assumed, there was an underlying story of progress.
Jump up ^ Andolfatto, David (31 March 2014). “Bitcoin and Beyond: The Possibilities and Pitfalls of Virtual Currencies” (PDF). Dialogue with the Fed. Federal Reserve Bank of St. Louis. Archived (PDF) from the original on 9 April 2014. Retrieved 16 April 2014.
Jump up ^ “Masternode vs Pruning Node vs Full Node”. The Merkle. Archived from the original on 16 January 2018. Retrieved 16 January 2018. Rather than storing entire network blocks full of data, the pruning node stores the final link of every transaction. Moreover, they can still validate bitcoin transactions and relay them to the rest of the network.
The bad news: Because it’s guesswork, you need a lot of computing power in order to get there first. To mine successfully, you need to have a high “hash rate,” which is measured in terms of megahashes per second (MH/s), gigahashes per second (GH/s), and terahashes per second (TH/s).
Well, before you invest the time and equipment, read this explainer to see whether mining is really for you. We will focus primarily on Bitcoin. (Related: How Bitcoin Works and our helpful infographic, What is Bitcoin?)
President Trump may have earnest reasons for his onslaught against Amazon, which he renewed Thursday morning on Twitter. But it’s the latest case where Trump’s previous statements suggest he has more personal, and dangerous, motives than he claims.
“When I first looked at the code, I was sure I was going to be able to break it,” Kaminsky said, noting that the programming style was dense and inscrutable. “The way the whole thing was formatted was insane. Only the most paranoid, painstaking coder in the world could avoid making mistakes.”
When a user loses his wallet, it has the effect of removing money out of circulation. Lost bitcoins still remain in the block chain just like any other bitcoins. However, lost bitcoins remain dormant forever because there is no way for anybody to find the private key(s) that would allow them to be spent again. Because of the law of supply and demand, when fewer bitcoins are available, the ones that are left will be in higher demand and increase in value to compensate.
In other words, bitcoin’s inventor Nakamoto set a monetary policy based on artificial scarcity at bitcoin’s inception that there would only ever be 21 million bitcoins in total. Their numbers are being released roughly every ten minutes and the rate at which they are generated would drop by half every four years until all were in circulation.[61]
Startups from all over the world began building specialised hardware powered by custom-built chips, known as application-specific integrated circuits (ASICs). Leaving the amateurs behind, these firms soon became locked in a digital arms race. Microprocessors usually double their power every 18 months, a rhythm called Moore’s law. In the case of mining ASICs, this doubling has occurred every six months.
#Facebook and #Twitter have banned #cryptocurrency advertising on their social media platforms but both FB co-founder Mark Zuckerberg and twitter CEO Jack Dorsey believe in the #blockchain technology and the bright future of #crypto!!https://cointelegraph.com/news/facebook-google-and-twitter-ban-ads-but-do-their-founders-really-dislike-crypto/ …
Dash is very much similar to Bitcoin is many ways, one of the main reasons being because they both use block chain as a database to run between updates of value with individuals that may not be 100% valid. The core difference with these systems is based on the government model, for example Dash is governed by owner Masternode, and Bitcoin is governed by third party via black chain. With Dash private transactions can be made with no connection to a person identify much like Bitcoin and other similar platforms.
Bitcoin mining is intentionally designed to be resource-intensive and difficult so that the number of blocks found each day by miners remains steady. Individual blocks must contain a proof of work to be considered valid. This proof of work is verified by other Bitcoin nodes each time they receive a block. Bitcoin uses the hashcash proof-of-work function.
To keep blocks coming roughly every 10 minutes, the difficulty is adjusted using a shared formula every 2016 blocks. The network tries to change it such that 2016 blocks at the current global network processing power take about 14 days. That’s why, when the network power rises, the difficulty rises as well.
This danger exists in large part because grasping even the basics of blockchain technology remains daunting for non-specialists. In a nutshell, blockchains link together a global swarm of servers that hosts thousands of copies of the system’s transaction records. Server operators constantly monitor one another’s records, meaning that to steal money or otherwise alter the ledger, a hacker would have to compromise many machines across a vast network in one fell swoop. Even as the global banking system faces relentless cyberattacks, the more than $30 billion in value on Bitcoin’s blockchain has proven essentially immune to hacking.
Almost all groups launching ICOs reiterate some version of this idea to potential buyers, in part as a kind of incantation to ward off financial regulators. The thinking is that, if they are selling part of a platform, rather than stakes in any company, they’re not subject to oversight by bodies like the U.S. Securities and Exchange Commission. But in practice, ICOs are constantly traded across a variety of online marketplaces as buyers breathlessly track their fluctuating prices. In this light, they look an awful lot like speculative investments.
Investing in cryptocurrencies and other Initial Coin Offerings (“ICOs”) is highly risky and speculative, and this article is not a recommendation by Investopedia or the writer to invest in cryptocurrencies or other ICOs. Since each individual’s situation is unique, a qualified professional should always be consulted before making any financial decisions. Investopedia makes no representations or warranties as to the accuracy or timeliness of the information contained herein. This article was first published on September 7, 2017, as of that date the author owned cryptocurrency.
There are some positive signals for Litecoin and February could invert this trend. The price is $170 at the moment and, in my opinion, it is a bit expensive. Any price below $160 should be considered.
The first hint of a meaningful challenge to the closed-protocol era arrived in 2008, not long after Zuckerberg opened the first international headquarters for his growing company. A mysterious programmer (or group of programmers) going by the name Satoshi Nakamoto circulated a paper on a cryptography mailing list. The paper was called “Bitcoin: A Peer-to-Peer Electronic Cash System,” and in it, Nakamoto outlined an ingenious system for a digital currency that did not require a centralized trusted authority to verify transactions. At the time, Facebook and Bitcoin seemed to belong to entirely different spheres — one was a booming venture-backed social-media start-up that let you share birthday greetings and connect with old friends, while the other was a byzantine scheme for cryptographic currency from an obscure email list. But 10 years later, the ideas that Nakamoto unleashed with that paper now pose the most significant challenge to the hegemony of InternetTwo giants like Facebook.
Also, the costs of being a mining node are considerable, not only because of the powerful hardware needed (if you have a faster processor than your competitors, you have a better chance of finding the correct number before they do), but also because of the large amounts of electricity that running these processors consumes.
When a block is discovered, the discoverer may award themselves a certain number of bitcoins, which is agreed-upon by everyone in the network. Currently this bounty is 25 bitcoins; this value will halve every 210,000 blocks. See Controlled Currency Supply or use a bitcoin mining calculator.