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      "memo": "Free Upvotes Await!!!, Vote @se-witness for one of your 30 witness votes. Once you do so, you will start accumulating free upvotes every 6 hours automatically.  Please check my latests posts for more info.  Thanks!"
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      "permlink": "steemitboard-notify-alphydan-20191110t032606000z",
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      "body": "Congratulations @alphydan! You received a personal award!\n\n<table><tr><td>https://steemitimages.com/70x70/http://steemitboard.com/@alphydan/birthday2.png</td><td>Happy Birthday! - You are on the Steem blockchain for 2 years!</td></tr></table>\n\n<sub>_You can view [your badges on your Steem Board](https://steemitboard.com/@alphydan) and compare to others on the [Steem Ranking](https://steemitboard.com/ranking/index.php?name=alphydan)_</sub>\n\n\n**Do not miss the last post from @steemitboard:**\n<table><tr><td><a href=\"https://steemit.com/steemfest/@steemitboard/steemfest-meet-the-stemians-contest-the-mysterious-rule-revealed\"><img src=\"https://steemitimages.com/64x128/https://cdn.steemitimages.com/DQmasWw4jQHwxng82DKxY6Q6tVg9mWcto4xcDURs8knFgCa/image.png\"></a></td><td><a href=\"https://steemit.com/steemfest/@steemitboard/steemfest-meet-the-stemians-contest-the-mysterious-rule-revealed\">SteemFest Meet The Stemians Contest - The mysterious rule revealed</a></td></tr><tr><td><a href=\"https://steemit.com/steemfest/@steemitboard/steemfest-meet-the-steemians-contest\"><img src=\"https://steemitimages.com/64x128/https://cdn.steemitimages.com/DQmasWw4jQHwxng82DKxY6Q6tVg9mWcto4xcDURs8knFgCa/image.png\"></a></td><td><a href=\"https://steemit.com/steemfest/@steemitboard/steemfest-meet-the-steemians-contest\">SteemFest⁴  - Meet the Steemians Contest</a></td></tr></table>\n\n###### [Vote for @Steemitboard as a witness](https://v2.steemconnect.com/sign/account-witness-vote?witness=steemitboard&approve=1) to get one more award and increased upvotes!",
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      "body": "Hello @alphydan! This is a friendly reminder that you have 3000 Partiko Points unclaimed in your Partiko account!\n\nPartiko is a fast and beautiful mobile app for Steem, and it’s the most popular Steem mobile app out there! Download Partiko using the link below and login using SteemConnect to claim your 3000 Partiko points! You can easily convert them into Steem token!\n\nhttps://partiko.app/referral/partiko\n\n![](https://d1vof77qrk4l5q.cloudfront.net/statics/partiko-poster-best-steem-app-for-your-phone.jpg)",
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      "author": "alphydan",
      "permlink": "what-in-the-world-is-bitcoin",
      "title": "What in the world is Bitcoin?",
      "body": "This post is a basic introduction to the technology behind Bitcoin. It is based on a talk I gave a few months ago.  The audience was assumed to know very little about the technology.\n\n![output-0.jpg](https://cdn.steemitimages.com/DQmY7WLL12QA58ptLXqzGdXZz29mdeMDzBiiv3REdhjpk5m/output-0.jpg)\n\nProfessionally, I juggle several hats. I am a physicist, a teacher, a coder and I understood [the potential of Bitcoin early on](https://alphydan.svbtle.com/the-big-book-of-bitcoin). As a physicist and programmer, I am fascinated by complex systems and have been studying cryptocurrencies since 2011.\n\n![output-1.jpg](https://cdn.steemitimages.com/DQmZLFqyBEXcD9uBmDmL7JGwZZCGYEGggHnh8g33xHxs1Pn/output-1.jpg)\n\nI was asked to give a talk on cryptocurrencies. I was meant to answer the question What in the world is Bitcoin?. But that's easy, I said!\n\n![output-3.jpg](https://cdn.steemitimages.com/DQmVf411r9xc83VCsb2C9iZAkSfUiRJuQc2fzYkbqo1jvDA/output-3.jpg)\n\nWell, yes. Sure. But, how does it work?, and What is it exactly?. To which I replied, That's easy too! `It’s an electronic, pseudonymous, decentralized, proof-of-work blockchain based crypto-currency`.\n\nAnd my audience kinda raised their eyebrows ...\n\n![output-11.jpg](https://cdn.steemitimages.com/DQmRpGPnCtzJWSn498mHCJnb12UmB94cDF998Dnqu2r4xis/output-11.jpg)\n\nOK. Let us start from the beginning.\n\n## 1. It is an Electronic Currency\n\n ![output-13.jpg](https://cdn.steemitimages.com/DQmQVtQ6RAmQDEyhGcetUdn6qKyJzW3hHs1BKZKnDCqAgGk/output-13.jpg)\n\n\nSo you can pay for stuff, send it, store it. But it only exists as ones and zeroes on computers. It’s digital money. Now some people might say: “Well, if you can’t touch it or store it like *real money*, how can you trust it?”. Well, I have news for you.\nThe vast majority of dollars or euros are already digital. Last night I made this graph, where the area is proportional to the trillions of dollars in circulation in the world.\n\n\n![output-15.jpg](https://cdn.steemitimages.com/DQmRj4HZbZu2L3JzfLitcrDu3ogWTZM2ksZ2vX5sBbyFq3v/output-15.jpg)\n\n\n The yellow square is cash (banknotes, coins, checking deposits). The next one is stocks, and then debt, followed by hundreds of trillions in derivatives. Everything which is not yellow is already digital. So your bank does not have the cash you may think it does. 90% of money today is digital [1,2,3].\n\n As a reference, I have added gold (the tiny rectangle on top of cash), and Bitcoin … the even smaller dot left of cash (As of Summer 2018). It is very small but, surprisingly, you can see it. All right, so I said that Bitcoin is an electronic currency. But that’s not very special. Most currency is electronic currency. So what’s the big deal then?\nWell, the important bit is all the mumbo jumbo in the middle, … blockchain, decentralized, etc, etc. We could, in fact, rephrase it and say that Bitcoin is an:       \n\n![output-17.jpg](https://cdn.steemitimages.com/DQmeWnwf2zcTjhvRYDcJPLW8QoGsrzvXAis3of3VSHyxKEo/output-17.jpg)\n\nBitcoin is an electronic currency on a magic ledger. Ok it’s not magic, magic … but we can say that Bitcoin is an electronic currency on a very special ledger. Actually, I am going to go a little further and say …\n\n\n![output-19.jpg](https://cdn.steemitimages.com/DQmbKCaue8g3yBrXs5BEsQYGMawTzN6qEwh1F9ib2Q13DV2/output-19.jpg)\n\nIf you don’t know what a ledger is, you can imagine an account book to keep track of transactions (debits & credits).  One page might look like this:\n\n![output-20.jpg](https://cdn.steemitimages.com/DQmTGHAS9subGWpdGw39mwQhbpH7t7umstatJTJbg6Xv7M5/output-20.jpg)\n\nIt might say:\nJoe has 2.2 BTC\nAlice has 1 BTC\nRuna has 0.0042 BTC\nAnd let’s say Joe wants to pay Alice one bitcoin. \n\n![output-21.jpg](https://cdn.steemitimages.com/DQmP1Yg5zRDzor1JcTaVZKdQ8rF4Uoorkfk1mmac8czvyPG/output-21.jpg)\n\nAll that needs to be done is update the ledger with the new balances. \n\n![output-22.jpg](https://cdn.steemitimages.com/DQmUwMmqSuVhAtW4MR4vKFY8r8H8THdB8u9AuzJNutAn2zo/output-22.jpg)\n\nAt this stage ... newcomers to Bitcoin usually think:\n\n![output-23.jpg](https://cdn.steemitimages.com/DQmfE4ijNK7dvdgtErmMob8VSo6da3CBRMbKtPxfAtHQbW4/output-23.jpg)\n\nWell, Those are exactly the right questions. That's precisely **where the Bitcoin magic happens**. Let's start with the first question.\n\n### Who updates the ledger?\nLet's think about the traditional banking system. Your accounts, payments or mortgages are also kept in an electronic ledger. \n\n![output-26.jpg](https://cdn.steemitimages.com/DQmR9gswkvN8TDCG2VRZA2kiPyPonA8LkRyxxxSxo5cSbTz/output-26.jpg)\n\nTraditionally when you make a payment, your bank shifts a number in a register. Or the central bank issues credit to banks. They are the ones updating the ledgers. Or perhaps an intermediary like MasterCard sends a request to update the ledger. In any case, you are certainly not allowed to update the balance in your bank account. For that, you need to trust your bank. The update of the ledger is done by:\n\n\n![output-27.jpg](https://cdn.steemitimages.com/DQmWbTSp2tTfXKsVudmbFVaUH6nK2J5dq6xmrhSboF262mz/output-27.jpg)\n\nA trusted, central authority (or an intermediary who charges for doing so).  The Bitcoin ledger, however, is very different.\n\nThe bookkeepers are **those who chose to participate**. A good slogan at the beginning could have been:\n\n![output-30.jpg](https://cdn.steemitimages.com/DQmcEB5BG4YQHCMHMzMD3ZL34qSXSfJJ8k8r3EDaUPepbKs/output-30.jpg)\n\nSo let's recap. We have a number of bookkeepers, all online, and there is a ledger.\n\n![output-32.jpg](https://cdn.steemitimages.com/DQmeexPpHQuE7TdrHgUuHeWWnt86nf5ZmxwxRpqxx1KY7ud/output-32.jpg)\n\n## 2. It is an Electronic Pseudo-Anonymous Decentralized Currency\n\nNow, our sentence had two interesting adjectives: Bitcoin is **pseudo-anonymous** and **decentralized**. Pseudo-anonymous means that the ledger looks more like a Swiss bank account than a list of names. If you look at the ledger you will see something like this.\n\n![output-34.jpg](https://cdn.steemitimages.com/DQmUU3Q2mu5KoY9n48h5UrC1Z62uAs3JXtUPLHjt9rGj424/output-34.jpg)\n\n- Bitcoin account *1VayNert3x1KzbpzMGt2qdqrAThiRovi8* has 2 BTC,\n- Bitcoin account *15JhBLtCWaDqrMrgcyDhu7m62TVZxgrtj8* has 0.018 BTC,\n- etc\n\nbut you don’t know who owns what. It's just an account identifier and a balance. The second aspect is that the ledger is **public** and **distributed**. This means that anyone in the world can go and read the books. Anyone! For example, want to see all the donations received this year by Wikileaks? [Go ahead](https://www.blockchain.com/btc/address/1HB5XMLmzFVj8ALj6mfBsbifRoD4miY36v). Anyone can read any and all bitcoin addresses, and all transactions from the creation in 2009. In fact, a better picture of the network would look like this:\n\n![output-37.jpg](https://cdn.steemitimages.com/DQmSGew1DbNtcaDDEUnpg5RKYKDgbx2qTjdYwBBzcKQtEWZ/output-37.jpg)\n\nWhere all accountants have a copy of the ledger. That's what is meant by distributed. But then ...\n\n![output-38.jpg](https://cdn.steemitimages.com/DQmY1YJp47KdYC4WHT7bebWJTShEk1Szk8oHN11xPugAVVw/output-38.jpg)\n\nAnd this is the very heart of the question. The very reason Bitcoin matters, and why it has been so successful. Let's follow an example to see how it happens. Imagine Peter wants to buy a smoothie and needs to pay Allie. To do so, **0.001 BTC** from his account needs to find its way to Allie's account.\n\n![output-40.jpg](https://cdn.steemitimages.com/DQmcXWAM2iuokmYzLNo9Zk3s4xWPDyNRheANExrE4TWbcrh/output-40.jpg)\n\n (By the way, 0.001 Bitcoin is sometimes called a miliBitcoin or **mBTC** for short). To do so, Peter's phone sends a message on the internet saying:\n> Please remove 0.001 BTC from `1EiwDW9VjTUbLJtuPYUkbj5fJDnc36WKdz` \nand deposit it in the account `1AxZb1Nqh7TPWURjLbDUQsSpUQZnF5cqLe`.\n\nThe actual process is: *Scan a QR code, type password, send*. But the concept is the same:\n\n![output-42.jpg](https://cdn.steemitimages.com/DQmVqqtvv6CWDpm8RjYVSgAYTL7UYqPZfDQrUrdqHeP1qCw/output-42.jpg)\n\nPeter's message will be relayed to all the accountants on the network who now have to update the books. To give you a sense of scale, every 10 minutes, transactions worth $11 million were being added to the ledger (in Jan 2019). But what incentive would they have to do that job? Well, to compensate them for their effort, their knowledge, and their computers ... one bookkeeper will be awarded 12.5 BTC at random. You might wonder: **Who are these people?** Who are these hard-working, ledger-updating bookkeepers? Well, let me introduce you to a real-life Bitcoin bookkeeper:\n\n![output-45.jpg](https://cdn.steemitimages.com/DQmUhBndTGfsbSbUWJyrqyCzp4vBeCkwFdgKX2dQqwsLjs6/output-45.jpg)\n\nYes. They are machines. Machines constantly running the Bitcoin bookkeeping software. So an even more accurate picture of the Bitcoin network would look like this:\n\n![output-46.jpg](https://cdn.steemitimages.com/DQmcmvpUPUsS5K8Giv1KujECE3Z5NxXbwGa7Te4D2zXoTr7/output-46.jpg)\n\nYou might be asking yourself ... couldn't people easily cheat? Let's go back to our friend Peter.\n\n![output-48.jpg](https://cdn.steemitimages.com/DQmQ5WMgDdt3jMXouDhFpLv5KKREn9JZmWZNgWFhCxQWu3x/output-48.jpg)\n\nLet's say he has a total of 1 bitcoin in his account. What if he sends 1 bitcoin to Bob … And then, immediately, tries to send one bitcoin to Allie as well. Maybe the bookkeepers in Hong Kong have not processed his transaction yet! Maybe he sends both almost simultaneously trying to get both in the ledger. This is the now famous *Double Spending Problem*.\n\n![output-51.jpg](https://cdn.steemitimages.com/DQmRwA2fvporKPX1NcWhG6Yt4Ecyc1UnEVvKdCM8r8sCgL6/output-51.jpg)\n\nHow can bookkeepers prevent that? Perhaps even more concerning is the following. When Peter paid Allie, he sent a message to the bookkeepers saying:\n\n> Please remove 0.001 BTC from `1EiwDW9VjTUbLJtuPYUkbj5fJDnc36WKdz` and \ndeposit it in the account `1AxZb1Nqh7TPWURjLbDUQsSpUQZnF5cqLe`.\n\nBut at least that was his account. What if he sent a message to pay from an account that wasn't his?\n\n![output-53.jpg](https://cdn.steemitimages.com/DQmaf3hxXgrUVuqrLB3nK2PaqPEEEKzcPPjbjMHYzF1vHzM/output-53.jpg)\n\nIn other words: how do we know Peter is who he says he is? And how do we know who sent what?\n\nAnd come to think of it, is there any warranty of not having rogue bookkeepers? They could also add incorrect balances. In fact, we should not trust them at all!\n\n## 2. The heart of Bitcoin\n\n![output-57.jpg](https://cdn.steemitimages.com/DQmTPo5cFVMKRYsA8PVKwug6DnxZtvtF5XyLoDRi8EFEf7x/output-57.jpg)\n\nWe are now ready to venture into the heart of Bitcoin's innovation, but to do so we will need some mathematics. If you are not familiar with cryptography, do not fret! We will need to consider something called a **Hash Function**. But I usually call them:\n\n![output-61.jpg](https://cdn.steemitimages.com/DQmYox1ALMDiVaXDjioqg4dN1kNGF1eKfd2T9cTT3tAGKhe/output-61.jpg)\n\nAs I think this describes them better. So what do they do? Simply put: they create summaries. Think of it this way. Imagine I have a summary box and I feed it the whole text from *Romeo and Juliet*. It might output something like this:         \n\n> Romeo & Juliet in love. Parents don't approve. Drama ensues.\n\nAnd we could ask ourselves: What if we change the name of a main character in the text? Well, a summary box would change the summary accordingly:\n\n\n![output-63.gif](https://cdn.steemitimages.com/DQmUCoGqNfnBsHwtW6tc44Y3rRY7uAJU5b5UPVRoMe1ZvJd/output-63.gif)\n\n\nBut this is not the type of summary box we need for Bitcoin. The ones used for Bitcoin (and secure banking) make different summaries. They look closer to this:\n\n![output-65.jpg](https://cdn.steemitimages.com/DQmYHtamJ5EswxnRbBwp47q3QXQK6SXv22x87aDaUefyoc9/output-65.jpg)\n\nIn other words. You input text and you get gibberish out. However, this summary box does something surprising. If you change anything in the input (even a single letter), the output becomes utterly different. Completely unrelated.\n\n\n![output-66.gif](https://cdn.steemitimages.com/DQmbNHj85pkJeDA8hdv8Bz8ASaf8QYbbytrzP4bEJvg8tjy/output-66.gif)\n\n\nTo give you a more dramatic example. You could feed the entierety of wikipedia to the box and get the tiny gibberish summary. Change a comma, and the summary will become unpredictable and seemingly unrelated.\n\n![output-68.gif](https://cdn.steemitimages.com/DQmTffqu4iDaMZBeyoV2nC7BoApaekmhAiotTzGaGYSi2FU/output-68.gif)\n\nNow, I hear you. It sounds like a pretty sad summary machine. What good is an unpredictable summary which looks like gibberish? Well, it is useful for security. The key concept is that by looking at a summary we can't know what created it. Was it the word `dog`? Was it your neighbour's `social security number`? Was it the complete works of Shakespeare with one letter altered? We can't know *a priori*. A good Hash function has two properties:\n\n- The same input creates the same output (Always!)\n- The output is impossible to reverse.\n\nThe only way to find the input would be to try every single option.\n\n![output-72.jpg](https://cdn.steemitimages.com/DQmdCAd2iH2zvT5GtifUWVVRu9z8XxKTHpF13b6SjJGrqMF/output-72.jpg)\n\nAs you can imagine, that could take a very, very, very long time. Imagine trying Wikipedia. Then Wikipedia with one word changed, two words changed, etc, etc. Essentially impossible.\n\nOk, so we have these funny boxes. How does the Bitcoin network use them? Let's get back to Peter. Peter was trying to trick the bookkeepers by sending the message `send money from Julia's account to this other account`. How can Julia, _and only Julia_, request such a transaction? To do so, she needs to sign her transaction. We can picture it like this:\n\n![output-73.jpg](https://cdn.steemitimages.com/DQmcwaT7peWPKRhGjZUjZWuj4pjPRYuCHiqv76V4TEjK3g6/output-73.jpg)\n\nBut of course, if she sends a picture of her signature, anybody can copy it and pretend to be her. Instead, she uses a digital signature (a bunch of ones and zeroes).\n\n![output-74.jpg](https://cdn.steemitimages.com/DQmPxF3BWyF4vDqTsk3D2nnreX6kY4YD9mEqX1DZk1vDwej/output-74.jpg)\n\nThe digital signature is, effectively, the password to her account. This may sound like an even worse idea! It's even easier to copy-paste a password than pictures. And you are right. \n\nThe solution to this problem is to take the signature and the requested transaction and pass it through a _magic summary box_. And of course, out comes unpredictable gibberish. And more importantly, it's impossible to know what the signature was (Since it is impossible to reconstruct the message that created the gibberish).\n\n![output-75.jpg](https://cdn.steemitimages.com/DQmf6wmLcTqHvwR19mSVJ27MSUj2wjJqYi41B97bbeHHWXk/output-75.jpg)\n\nThe message she will upload will now look like this:\n> please transfer 100 BTC from account `6Yr4nT0ppJVSXYPq0PQzSDEfJDnc36SAxm` to account `1AxZb1Nqh7TPWURjLbDUQsSpUQZnF5cqLe`. To prove that I am the owner of the account, here is my transaction added to my signature/password and passed through a magic summary box: `b2fa3d8e577402cf5654dbf559d89702c33db73667fa38fba4bdebdb924c1fb9`\n\nMathematicians have been able to find a second type of summary box. I call it the **Magic Verify Box**. This is a box that the bookkeepers have. Their question is: _is it true that Julia is the owner of the sending account?_ Banks will ask you for your password, or parts of your password to ascertain this. But Bitcoin uses clever math to get around it. The Verify Box can read the transaction request, the gibberish summary, and say:\n\n![output-79.jpg](https://cdn.steemitimages.com/DQmcVCBT2xWF3y2iVopgZJgVoNumddCtSi3bzuejJCifW3n/output-79.jpg)\n\nAnd it can do so without ever knowing the password (what we called the digital signature, earlier). Remember that Julia sends the _signature or password_  + _transaction_ through her summary box which scrambles everything beyond recognition. And yet, the accountants can be sure that she signed it with her password. Such is power of cryptographic hashing algorithms (also known as public key cryptography).\n\nMore importantly, if Peter tries to send a transaction pretending to be Julia, it is immediately blocked, as he does not have the secret signature (or password).\n\n![output-81.jpg](https://cdn.steemitimages.com/DQmNSXBxUhND7R6wU1a5fXujjWyj98eLjzZ9juc46B5GyUm/output-81.jpg)\n\nYou might have heard of a Bitcoin wallet. You are now ready to know what it means. It is just two numbers: A \"bank account number\" and a \"password\".  \n\n![output-82.jpg](https://cdn.steemitimages.com/DQmUexC4SMUVZdy5XieGcszpRUdaj1ub4KPrum4pXnPEz72/output-82.jpg)\n\nThat's all a wallet is.  In other words: the address with the Bitcoin, and the signature (or secret password) that allows you to spend. In the Bitcoin lingo, we call them:\n\n- The public address (the account number on the ledger)\n- The private key (the secret signature)\n\nThis is what two such numbers look like:\n\n![output-85.jpg](https://cdn.steemitimages.com/DQmWcnNcmXKxyxjnqvEZBnp2KaEjJN7ccgLhPEyokHjQ9gT/output-85.jpg)\n\nIf you combine those two numbers, your transaction details and send them through a summary box, you have spent Bitcoin on the Internet. Of course this all happens behind the scenes. Users just click a button.\n\n## 3. The Blockchain\n\nWe have now covered most words inside\n\n> **Electronic pseudo-anonymous**, **decentralised**, proof-of-work blockchain based **crypto-currency**.\n\nOur last word was **crypto**, which refers to the use of these mathematical _boxes_ that enable to spend securely without revealing passwords.\n\nNow, as I explained, when you input something new into a _summary box_ it is impossible to predict what will come out the other end. Then somebody had a brilliant idea. \n\nWhy don't we pass the full ledger through the box?!\n\n![output-89.gif](https://cdn.steemitimages.com/DQmVerqFPueTFkvXdhSxUtdXfXA6rPNcSzQgFmPjCNhLAhb/output-89.gif)\n\nThe gibberish summary which it spits out would be an **impossible to forge** summary.\n\nWhy? Because if you were to change a single digit, a single comma, a sign, a cent of a Bitcoin in someones' account, the whole summary would change. And this is indeed what happens. Every 10 minutes a new summary of the entire accounting since 2009 is made.\n\n![output-91.gif](https://cdn.steemitimages.com/DQmd6r8P7AsLz3mtwvQsGxF62YRUVDSqbZdBJmGkZvyP8tQ/output-91.gif)\n\nIf anybody was ever to change any character, it would be instantly obvious.\nIf you have heard the term Blockchain before, you should understand it now. Every 10 minutes a new block is added to the ledger. Bookkeepers take the previous summary (now set in stone), and append the transactions from the last 10 minutes. This new ledger itself is passed through the summary box and set in stone as the last valid version.\n\n![output-92.jpg](https://cdn.steemitimages.com/DQmWuuPtMF3ZizWrhyPbvSKKz2V24ve4g77eDpAcoF9u3nE/output-92.jpg)\n\nThis chain of verified summaries is called **the Blockchain**. You will also see it called an **immutable ledger**, since nothing can be changed without altering each summary.  Now, you might be thinking. Ok, so you can't change the past.\n\n![output-95.jpg](https://cdn.steemitimages.com/DQmTYJnErvurhHkRFFsSRE4XqnqXFqQpbBuHYGMT5KoRy98/output-95.jpg)\n\nBut what about those crucial 10 minutes before it's stamped into the block summary? Could bookkeepers cheat in those critical 10 minutes.\n\nAnd that, my dear reader, is the final piece in our puzzle. [Bitcoin's creator](https://en.wikipedia.org/wiki/Satoshi_Nakamoto) married several existing technologies and ideas to solve this difficult conundrum. The last piece of the puzzle is the last word in our description of Bitcoin:\n\n## 4. The proof in the pudding\n\n> Electronic pseudo-anonymous, decentralised, **proof-of-work** blockchain based crypto-currency.\n\nTo solve the problem of cheating while the current block is being agreed upon, Bitcoin has an incessant bookkeeper competition. The challenge that bookkeepers need to solve is the following:\n\n- Pick a number or letter,\n- append it to the current accounting ledger\n- and pass the result through the magic summary box\n\n> `> If the output starts with 18 zeros, you win 12.5 Bitcoin. `\n\nNow, remember that it's impossible to guess which input creates a certain summary. The only way to do it is to try all possible options and hope that one works. So each bookkeeper is trying:\n\n- 1 + the last summary\n- 2 + the last summary\n- 3 + the last summary\n- ...\n- 23af + the last summary\n\nUntil one lucky bookkeeper hits the jackpot!\n\nCurrently (Jan 2019), finding the lucky number gets you the equivalent of $48,000 USD. And this happens every 10 minutes! So guess what people started doing? They started buying multiple computers and having them running day and night trying to find that number!\n\n![output-103.jpg](https://cdn.steemitimages.com/DQmPnWAAqEzHMQhQLwUYPA8DBw6PZSbF4L1N4XQ8Mn6sxvt/output-103.jpg)\n\nToday, entire server farms are dedicated to finding the number which is appended to the next block. As you can imagine, if you find a few, it can be very profitable. **But how does this protect the network from cheating?**\n\nThe [details](https://blockchainatberkeley.blog/understanding-crypto-economic-security-through-game-theory-526e810c7736) are [complex](https://www.coindesk.com/bitcoins-security-model-deep-dive/), but the essence is that, as a bookkeeper, it does not pay to cheat. In other words, if you spend your computer resources trying to alter your balance on the blockchain, somebody else will find the number which validates the correct transactions. So if you try to cheat, the rest will get ahead of you and you are unlikely to get the 12.5BTC prize!\n\n![output-106.gif](https://cdn.steemitimages.com/DQmdUkF8xJpJkz5g8tHeBUNmxtVYv3giXG77YVsGq3zkBUs/output-106.gif)\nThe reward in summer 2018 was $94,000\n\nThere is a lot more to this process. But this article will stick to the essentials.  One essential observation is that this is how the currency is created.  All coins ever issued were a reward to those bookkeepers on the Bitcoin network. The coin is issued as a reward for the bookkeeping process. In the Bitcoin lingo, the bookkeepers are actually called **Bitcoin Miners**. Since they are searching for those elusive coins, their job is also called **mining**. But the objective of their job is to keep the network secure. The rules on Bitcoins creation are more involved, but the above captures the gist.\n\nThe actual Bitcoin protocol adjusts the reward (it will be less than 12.5 BTC in the future), adjusts the difficulty of finding the next block, and prioritises transactions depending on the fees paid.  Finally, only 21 million bitcoins will ever be issued, and transfer fees will fund the “bookkeeping” thereafter. \n\nIf you think about it longer, you will find out that there is a risk if too many (more than half) of the bookkeepers conspire. This is indeed the case and much study and energy has gone towards preventing this.\n\nBy now, you should understand our first description of Bitcoin. It is an:\n\n> Electronic pseudo-anonymous, decentralised, proof-of-work blockchain based crypto-currency.\n\nBut more than that, it is the first time in history that anyone in the world can participate in a decentralized global economy without asking for permission, without a bank, at the click of a button.\n\n![output-108.jpg](https://cdn.steemitimages.com/DQmeNDZEM1emwCaPnx5S2hGBvi4H3UGHNmnFhtrhkBZPgiL/output-108.jpg)\n\nThe IMF director had this to say about it:\n\n![output-109.jpg](https://cdn.steemitimages.com/DQmXZbQ9xmxH3SAmSgosbho5ojWr1zvcNWseuKf5wx5xKRd/output-109.jpg)\n\nPersonally, I find it a fascinating social and technological experiment. I [said as much in 2013](https://alphydan.svbtle.com/the-big-book-of-bitcoin) and it hasn't disappointed. The future of cryptocurrencies is an open question that we will answer as a society but the possibilities are fascinating.\nTo keep this article accessible to the general public, several simplifications were made and some subtleties were omitted. If you want a more technical details I can recommend [3Blue1Brown's video](https://youtu.be/bBC-nXj3Ng4), Michael Nielsen's [Bitcoin protocol explanation](http://www.michaelnielsen.org/ddi/how-the-bitcoin-protocol-actually-works/), or Ander's Brownworth's [blockchain demo](https://anders.com/blockchain/).\n\nThis article is published with License [`CC-BY`](https://creativecommons.org/licenses/by/4.0/)\n\n## References\n\n[1] https://www.federalreserve.gov/releases/h6/current/default.htm \n[2] http://www.investopedia.com/tech/how-much-worlds-money-bitcoin/ \n[3] http://www.marketwatch.com/story/this-is-how-much-money-exists-in-the-entire-world-in-one-chart-2015-12-18 \n[4] [The Math behind Bitcoin](https://www.coindesk.com/math-behind-bitcoin)\n[5] [The slides from the original talk](https://speakerdeck.com/alphydan/what-in-the-world-is-bitcoin-2017/)",
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"https://www.coindesk.com/bitcoins-security-model-deep-dive/\",\"https://youtu.be/bBC-nXj3Ng4\",\"http://www.michaelnielsen.org/ddi/how-the-bitcoin-protocol-actually-works/\",\"https://anders.com/blockchain/\",\"https://creativecommons.org/licenses/by/4.0/\",\"https://www.federalreserve.gov/releases/h6/current/default.htm\",\"http://www.investopedia.com/tech/how-much-worlds-money-bitcoin/\",\"http://www.marketwatch.com/story/this-is-how-much-money-exists-in-the-entire-world-in-one-chart-2015-12-18\",\"https://www.coindesk.com/math-behind-bitcoin\",\"https://speakerdeck.com/alphydan/what-in-the-world-is-bitcoin-2017/\"],\"app\":\"steemit/0.1\",\"format\":\"markdown\"}"
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      "body": "Congratulations @alphydan! You have received a personal award!\n\n[![](https://steemitimages.com/70x70/http://steemitboard.com/@alphydan/birthday1.png)](http://steemitboard.com/@alphydan)  1 Year on Steemit\n<sub>_Click on the badge to view your Board of Honor._</sub>\n\n\n**Do not miss the last post from @steemitboard:**\n<table><tr><td><a href=\"https://steemit.com/steemfest/@steemitboard/steemfest3-and-steemitboard-meet-the-steemians-contest\"><img src=\"https://steemitimages.com/64x128/https://cdn.steemitimages.com/DQmeLukvNFRsa7RURqsFpiLGEZZD49MiU52JtWmjS5S2wtW/image.png\"></a></td><td><a href=\"https://steemit.com/steemfest/@steemitboard/steemfest3-and-steemitboard-meet-the-steemians-contest\">SteemFest3 and SteemitBoard - Meet the Steemians Contest</a></td></tr></table>\n\n> Support [SteemitBoard's project](https://steemit.com/@steemitboard)! **[Vote for its witness](https://v2.steemconnect.com/sign/account-witness-vote?witness=steemitboard&approve=1)** and **get one more award**!",
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      "body": "*\"What should we call each other?\"*,  said Isobel. *\"Well, we could always start with Mrs Crawley and Lady Grantham\"*, replied Violet.  With that dialogue we are ushered into [Downtown Abbey\n](http://en.wikipedia.org/wiki/Downton_Abbey), a British country house where a TV drama unfolds at the beginning of the XXth century.  \n\n![Downton Abbey Castle](http://upload.wikimedia.org/wikipedia/commons/thumb/b/b7/Highclere_Castle.jpg/638px-Highclere_Castle.jpg)\nHearing the servants talk to each is a striking reminder of how much language has evolved: *\"Might I remind you we are preparing dinner?\"* sounds too convoluted today.   Watching the show from a XXIst century perspective you can't help but ask: \n\n**Why all the formal language?**\n\nAnd why all the formal demeanour and manners? The Edwardian period shows more restraint and control.   Physical contact is rare, communication is less explicit and sentences are generally longer (sometimes because the message carries additional information like class, deference or sarcasm).\n\nToday, even in the upper strata of society, we are less formal, more explicit, more relaxed with our posture and less strict in our use of the language.  Will this trend continue? And if so, where could it take us?\n\nWill we use shorter, informal utterances?  Will our posture be even more relaxed (feet on the table, crouching and slouching) and will our sentences become even simpler?  \n\nAn obvious example is *[TXT-speak](http://en.wikipedia.org/wiki/SMS_language)*, where abbreviations, slang and pictograms enable rapid written communication.  Many adults are horrified, but wouldn't a XIXth century aristocrat and scholar be horrified by our casual conversations?\n\nThis travel through the evolution of language led me to make a bolder extrapolation:  Could we dispense with the written word in the future?  It may seem completely unrealistic, but current technology trends suggest it's not so far-fetched. Consider the following:\n\n* Young people are reading less [1], [2], [3]\n* People are consuming more images and video [4]\n* Computers are getting better at simulating reality [5], [6]\n\nWe are certainly not there yet, but according to [certain estimates](http://www.newscientist.com/article/dn13585-matrixstyle-virtual-worlds-a-few-years-away.html) supercomputers are reaching the speed necessary to create realistic simulations of reality.  This means that you could be in a room, look around you, and not know if the walls and windows are real or simulated.  Light would behave the way physics dictates and no flickering would be perceived. \n\nNow imagine if this computing power became portable some time in the future.  Would you write your story or would you let people live the story in a virtual world.  Wouldn't that chapter on the Han Dynasty be more engaging if you could travel to 200 BC Chang'an and meet the emperor Gaozu.  All set in a 3d setting indistinguishable from reality (ignoring smell, taste, and the sensory experience).  The simulation could also include peasants, artisans ... or whatever details the artists and creators chose to include in their 'description'.  You would be able to explore both space (move) and time (pause, rewind, or fast forward).\n\n---\n\nThe hypothetical programming language for this world would give various primitives from which to build worlds:  3D landscapes, characters, animals, shapes, rules of physics, etc.  And of course other stories would be possible:  Like a lecture in mathematics where the concepts would come alive.\n\nCould these communication channel take over the written word?  Experiences would be shared as visual immersive experiences.  Fantasies or essays could be equally built using this format.\n\nSome will argue that this 3d-video experience (to give it a name) will never replace books or articles.  Wouldn't it hinder our imagination and creativity?  I don't think it would.\n\nThe written word was created to transmit thoughts and experiences, not because symbols on a flat surface are particularly human.  The written word certainly killed the minstrels (who also captivated the imagination of the audience with their masterful communication).  I think a 3D realistic and programmable environment which can be easily stored and retrieved could eventually substitute books, magazines and articles.  Creativity, imagination and the possibilities of content creation would simply be redefined.\n\nThe details of such a transition are of course difficult to predict.  Obvious unknowns are the timing, the hardware or even whether our civilization will continue to successfully develop technology given the energy and resource constraints. \n\nLanguages have evolved over millennia.  However, 600 years ago,  [the movable type printing](http://en.wikipedia.org/wiki/Johannes_Gutenberg) impacted literature, culture and religion which in turn influenced technology and language. Over the last 15 years, technology  has modified our communication again (examples are txt-speak, twitter, hyper-links, semantic web, or the dominance of English).   The next 20 years may see new and unexpected forms of communication arise.  Although I have mixed feelings about it ... I think I may live to see the decline of the written language.\n\n---\n\n[1]: [Young People Reading a lot less, 2007](http://www.boston.com/news/nation/articles/2007/11/19/young_people_reading_a_lot_less/?page=full)\n\n[2]: [OECD insights, Children reading less but enjoying it as much](http://oecdinsights.org/2012/09/17/children-and-young-people-reading-less-but-enjoying-it-as-much/)\n\n[3]:  [Statistics Brain on Reading](http://www.statisticbrain.com/reading-statistics/)\n\n[4]: [The Colossal Growth of Online Video](http://www.themediabriefing.com/article/video-ad-spend)\n\n[5]:  [Toward the Graphics Turing Scale on a Blue Gene Supercomputer - ArXiv](http://arxiv.org/PS_cache/arxiv/pdf/0801/0801.1500v1.pdf)\n\n[6]: [Practical Implementation of a Graphics Turing Test](http://vbn.aau.dk/en/publications/practical-implementation-of-a-graphics-turing-test%2893496a51-1e1d-40a5-afe3-8ab661a34636%29.html)\n\n[7]: [Virtual Reality Can Leave You With an Existential Hangover](https://www.theatlantic.com/technology/archive/2016/12/post-vr-sadness/511232/?single_page=true)",
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      "title": "Teaching Cyber Security (Part 17)",
      "body": "@@ -1057,16 +1057,129 @@\n word_.%0A%0A\n+!%5BATTENT03-60px.png%5D(https://steemitimages.com/DQmabPoqyfhTMGdspo7kkAk1UdwRJG8TsXdk2AJtwbtzZmn/ATTENT03-60px.png)\n **Rememb\n@@ -1250,17 +1250,17 @@\n ion, it \n-w\n+c\n ould be \n@@ -2612,71 +2612,10 @@\n from\n- and use them instead of trying to remember thousands of words\n .\n+ \n  So,\n@@ -2846,25 +2846,12 @@\n ern%0A\n-Then, usually the\n+Good\n  pas\n@@ -2861,60 +2861,156 @@\n rds \n-h\n av\n-e a %E2%80%9Cpattern%E2%80%9D to try to prevent or minimize \n+oid any type of pattern.  For example %60xna;weri21935y7213%60 is a good password, but %60horse%60 is not. The attack you are planning is called a _\n brute\n+ \n forc\n@@ -3021,105 +3021,79 @@\n tack\n-s (the ones that can be programmed by using %E2%80%9Cdictionary%E2%80%9D words, exactly what we are about to do\n+_.  That is because it tries all possible words (without any insight\n ).\n+ \n  In \n@@ -3103,17 +3103,42 @@\n s case, \n-t\n+I will give you a hint.  T\n he patte\n@@ -3234,11 +3234,13 @@\n be %E2%80%9C\n-foo\n+horse\n 5%E2%80%9D o\n@@ -3268,19 +3268,42 @@\n e do to \n-get\n+produce words which follow\n  such a \n@@ -4377,19 +4377,98 @@\n or (\n+%5B\n nano\n+%5D(https://en.wikipedia.org/wiki/GNU_nano)\n , \n+%5B\n gedit\n+%5D(https://wiki.gnome.org/Apps/Gedit)\n , et\n@@ -5238,86 +5238,37 @@\n er. \n-If we need that every single word is added every digit before reading the next\n+To have a number next to each\n  wor\n@@ -5273,23 +5273,24 @@\n ord, we \n-need to\n+will use\n  use a t\n@@ -5355,16 +5355,17 @@\n  of anot\n+h\n er loop.\n@@ -5584,40 +5584,98 @@\n ts? \n-OK, let%E2%80%99s go to the final part.%0A\n+Do you understand how it works?  But how can you use these passwords on the secret server?\n %0A%0A%0A#\n@@ -6039,169 +6039,9 @@\n lem%0A\n-Mostly because of security, the door can%E2%80%99t be %E2%80%9Ctoo open%E2%80%9D for attackers when you have a secure server which you try to prevent from being attacked. This is why, i\n+I\n f yo\n@@ -6118,19 +6118,19 @@\n t (with \n-its\n+the\n  right p\n@@ -6190,55 +6190,19 @@\n work\n- as expected.%0A%0A%0AWhy doesn%E2%80%99t it work as expected\n+.%0A%0A%0AWhy not\n ? Th\n@@ -6271,20 +6271,19 @@\n assword \n-that\n+for\n  the ser\n@@ -6286,19 +6286,18 @@\n  server \n-can\n+to\n  read. F\n@@ -6932,17 +6932,413 @@\n erver)%0A%0A\n-%0A\n+-------------%0A%0AI hope you enjoyed this course.  It should give you a good idea of all the tools that are used behind the scenes to manage servers, networks and to secure the Internet.  Keep learning to become an awesome %5BWhite Hat%5D(http://www.itpro.co.uk/hacking/30282/what-is-ethical-hacking-white-hat-hackers-explained) %5BHacker%5D(https://en.wikipedia.org/wiki/White_hat_(computer_security)).%0A%0A## \n Good luc\n",
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      "body": "@@ -77,17 +77,17 @@\n ub. Read\n-%0A\n+ \n %5B%5Bpart 1\n@@ -195,38 +195,8 @@\n ll%0A%0A\n-Welcome to Module 2, Unit 2.  \n By n\n@@ -293,28 +293,32 @@\n t using the \n+__\n Bash\n+__\n  language).%0A\n@@ -1272,16 +1272,22 @@\n  secret \n+server\n .  To do\n@@ -1371,16 +1371,17 @@\n is point\n+,\n  you sho\n@@ -1963,16 +1963,221 @@\n by hand.\n-\n \n+  %0A%0AIn fact, if the password has 8 characters (letters and numbers) there are 2,821,109,907,456 possible combinations.  If you try one every second, it will take you 800 centuries to try them all!!   (%E2%98%89_%E2%98%89)\n %0A%0A%3ESo wh\n@@ -2601,16 +2601,38 @@\n  → \n-\n \n+all the way to → \n 10,000. \n@@ -3715,33 +3715,33 @@\n  1, so do %60echo \n-x\n+1\n %60%0A- then x is 2,\n@@ -3749,25 +3749,25 @@\n so do %60echo \n-x\n+2\n %60%0A- then x i\n@@ -3783,17 +3783,17 @@\n o %60echo \n-x\n+3\n %60%0A- etc%0A\n@@ -4026,8 +4026,160 @@\n e shell?\n-\n \n+%0A%0ABut how then, do hackers use those loops to hack servers? Find out in %5B%5BPart 17%5D(https://steemit.com/linux/@alphydan/teaching-cyber-security-part-17)%5D\n",
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      "body": "This is the 17th post of a series for teaching cyber-security in a coding-club. Read [[part 16](https://steemit.com/linux/@alphydan/teaching-cyber-security-part-16)]\n\n# Putting it all together\n\n## Combining it all\nIn this unit we'll use what we have learnt in the previous units of this module. You will finally have all the tools to complete your original mission!\n\n## Finding the server\nDo you remember the tool we used to check if a server is up and running on the Internet? It's a part of the name of a game similar to tennis, but smaller.\n\nYes, it's `ping`.\n\nSo, if you `ping` our server, you should get `0% packet loss`.\n\n```\nping -c 5 example.org\n```\n \n\nGood! You found the server.\n\n![happy_face.jpeg](https://steemitimages.com/DQmS7EtWw9wzkVW49FSy7tZjvzbrxdMRBSyjz7dqTJZci4G/happy_face.jpeg)\n\n# Entering the server\nNext, for fixing the security, you have to get inside the server. Typically a _sysadmin_ (The server administrator) will let you into the server by giving you a set of credentials. Usually the credentials are a _username_ and a _password_.\n\n**Remember that if you try to log into a server without explicit permission, it would be considered a crime!**\n\nSo, to log into the server you would use the `ssh` command, indicating the username with the server:\n\n```\nssh username@server\n```\n\nYou should first get the prompt. Then, you have to type the password, and finally, press the **Enter** key. If you can’t see the letters or stars as you type your password, don't worry. It is the default behavior when you have to login into an ssh server, so you have to make sure you use the right keystrokes and press enter when finished.\n\n\n\n# Authorization basics\n\nUsually, without knowing the right password, whatever you type will be incorrect, so you have three chances to enter the right user and password, or you will be rejected. You can try again another combination, fail, and so on.\n\n![sad_face.jpeg](https://steemitimages.com/DQmYgPfy6pRZkgFY3Naza9efQhAMcHJaXn8qHxjhToke8tv/sad_face.jpeg)\n\nYou can be sure that this won’t get you into the server. It would take too much time, you would get frustrated, so you have to try something different. Ok, let’s forget this strategy and think of another.\n\n![relief_face.jpeg](https://steemitimages.com/DQmajZBhXvdpLsLqfDeaNU4kGYcUvdH4A39y7Jd3TRsHuc3/relief_face.jpeg)\n\n# The new strategy\nWe have agreed that we can’t be thinking and typing, trying, over and over until we get exhausted. So, as a first step, we need a source to get words from and use them instead of trying to remember thousands of words. So, where could you find lots and lots of words? Yes, in a dictionary.\n\nIf you remember, we had a text file with english words, _/usr/share/dict/american-english_. We can use the words in this file for our purpose.\n\n\n# The pattern\nThen, usually the passwords have a “pattern” to try to prevent or minimize bruteforce attacks (the ones that can be programmed by using “dictionary” words, exactly what we are about to do). In this case, the pattern for the password is a dictionary word followed by a digit between 0 and 9. So, it can be “foo5” or “bar3”.\n\nWhat can we do to get such a pattern? Well, first, we have to read the words, and then, we have to add a number to the word. What can we use to accomplish this? Did you guess loops?\n\n\n# Reading the text file\n\n## Reading a text file line by line\nWe know how to view the contents of a text file, but we need to do something else for each line before reading the next one, but let’s go step by step. Let’s just read the content of the file:\n\n `cat /usr/share/dict/american-english`\n\n### Do something inside a loop\nWell, that was the easiest part. Now, let’s do something beyond printing every line. For this, we have to create a loop and do something. You might remember that we used the `echo` command which means _print_ or _show in the shell_.\n\n\nInstead of typing all the commands in the shell, we can save them to a file and run them later.  The files containing shell programs should end with .sh, so let's create a file for your program.\n\n```touch mycode.sh```\n\nyou should now see your file on your file manager, with all the other files in your main folder. You can edit it with any text editor (nano, gedit, etc). \n\n\nWrite the following inside your file:\n\n ```\n for word in $(cat /usr/share/dict/american-english);do\n     echo “printing: $word”\n done\n ```\n\nWhen you are finished with editing, you can run the script from a terminal window by using ```“bash mycode.sh”```, and you should see every line of the text file with the text “printing: “ right in front of each line.\n\n### Something else in the text\nWe have just seen how to perform an action on each item inside a loop. Now, we need the action to be to add a single digit instead of echoing the same text every time. Now, let’s remember how to create a loop for numbers:\n\n ```\n   for number in {0..9};do\n       echo $number\n   done\n ```   \n\nNow that we have learned both separate actions, we have to put them together. If we need that every single word is added every digit before reading the next word, we need to use a technique called nesting. It is about nesting a loop inside of anoter loop. Let’s see how it works:\n\n ```\n   for word in $(cat /usr/share/dict/american-english);do\n      for number in {0..9};do\n         echo “is the password $word$number?”\n      done\n   done\n ```\n \nCan you see the results? OK, let’s go to the final part.\n\n\n\n# Trying combinations for the server\n\nThe script we have just written, loops through the dictionary and numbers and echoes what both loops have at the time. Our mission is to log into the server trying every single combination, until one works. Does it sound easy? Sadly, we need to face another problem before going further.\n\n\n# The automatic ssh login problem\nMostly because of security, the door can’t be “too open” for attackers when you have a secure server which you try to prevent from being attacked. This is why, if you just replace the `echo` command with the `ssh` command in your script (with its right parameters, of course), you will find that it doesn't work as expected.\n\n\nWhy doesn’t it work as expected? The `ssh` command doesn’t have a way to automatically supply a password that the server can read. For our mission, we need to install a tool that provides such capability. There’s more than one tool, but the easiest one is `sshpass`, so let’s proceed and install it.\n\n\n   `sudo apt install sshpass`\n\nIf you run the command `sshpass` in the shell, but add the option \"-h\" you will find a lot of information about how to use that program. If you read carefully, you should find:\n - That the -p option, followed by the password, can be very helpful.\n - That after the options, you have to type the command (`ssh` itself)\n - And that after the command, you have to type the arguments (i.e., the parameters for ssh to log into the server)\n\n\nGood luck in your mission!",
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      "body": "@@ -77,17 +77,17 @@\n ub. Read\n-%0A\n+ \n %5B%5Bpart 1\n@@ -158,16 +158,17 @@\n art-14)%5D\n+.\n %0A%0A%0A# Hos\n@@ -1198,36 +1198,31 @@\n %0A%0A%60%60%60%0Awhois \n-royalgazette\n+nytimes\n .com%0A%60%60%60%0A%0AWa\n@@ -1433,20 +1433,15 @@\n ois \n-royalgazette\n+nytimes\n .com\n@@ -2391,25 +2391,26 @@\n eroute w\n-ww.gov.bm\n+eb.mit.edu\n %0A%60%60%60%0A%0ATh\n@@ -2489,18 +2489,18 @@\n our \n-codio serv\n+own comput\n er a\n@@ -2510,26 +2510,19 @@\n the \n+MIT \n website\n- in Bermuda\n .  L\n@@ -2584,17 +2584,18 @@\n -n w\n-ww.gov.bm\n+eb.mit.edu\n  %7C a\n@@ -2980,24 +2980,103 @@\n iplookup%60.  \n-\n \n+First let's install the necessary tools:%0A%0A%60%60%60%0Asudo apt install geoip-bin%0A%60%60%60%0A%0A%0A\n Let's pipe t\n@@ -3203,16 +3203,17 @@\n %7B %7D%0A%60%60%60%0A\n+%0A\n This is \n@@ -3504,52 +3504,290 @@\n %60.%0A%0A\n-%0A# Secure shell%0A%0A## Connecting to a server%0A%0A\n+Try websites in different countries and find out what other countries your %60pings%60 jump through before you get the website.%0A%0A%0A# Secure shell%0A%0A## Connecting to a server%0A%0A!%5BATTENT03-60px.png%5D(https://steemitimages.com/DQmabPoqyfhTMGdspo7kkAk1UdwRJG8TsXdk2AJtwbtzZmn/ATTENT03-60px.png)\n **WA\n@@ -5102,66 +5102,65 @@\n %60%60%0A%0A\n-When you are done exploring, move on to the next page\n+Did it work? You can ask in the comments if it didn't\n .%0A%0A%0A\n-%0A\n # Co\n@@ -5303,11 +5303,11 @@\n the \n-BHS\n+XYZ\n  sec\n@@ -5740,16 +5740,50 @@\n ack \n-packages\n+information traveling through the internet\n )%0A%0AA\n@@ -5962,16 +5962,18 @@\n However \n+**\n it can o\n@@ -5979,24 +5979,26 @@\n only be used\n+**\n  if we are a\n@@ -6029,16 +6029,22 @@\n .%0A%0A!%5Bssh\n+_small\n .png%5D(ht\n@@ -6074,57 +6074,201 @@\n /DQm\n-XSqPfo4gspcqViiTjUybhT1MDRjRSEPH9ADT91AeXMiw/ssh.png)\n+VfpSP81MY6X1LZcurCAo5rC6g3gE6qQgWxkg977Jcq4m/ssh_small.png)  To learn more about ssh and small shell programs, visit %5B%5BPart 16%5D(https://steemit.com/linux/@alphydan/teaching-cyber-security-part-16)%5D\n",
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      "body": "@@ -5488,16 +5488,19 @@\n of Death\n+ %F0%9F%92%A5\n  (**PoD*\n",
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      "body": "@@ -77,17 +77,17 @@\n ub. Read\n-%0A\n+ \n %5B%5Bpart 1\n@@ -158,16 +158,17 @@\n art-13)%5D\n+.\n %0A%0A%0A# Pin\n@@ -519,16 +519,17 @@\n For that\n+,\n  we need\n@@ -541,16 +541,21 @@\n ry very \n+very \n brief in\n@@ -855,16 +855,71 @@\n all.jpg)\n+%0Asource: %5Bwww.opte.org/maps%5D(http://www.opte.org/maps/)\n %0A%0ASome o\n@@ -1205,42 +1205,43 @@\n  %6034\n- Bermudiana Road, Hamilton, Bermud\n+4 Kublai Road, Ulaanbaatar, Mongoli\n a%60. \n@@ -1465,37 +1465,38 @@\n  %6034\n-.BermudianaRd.Hamilton.Bermud\n+4.KublaiRd.Ulaanbaatar.Mongoli\n a%60, \n@@ -1595,11 +1595,14 @@\n The \n-BHS\n+School\n  com\n@@ -1847,22 +1847,22 @@\n  7e:\n-8\n+6\n 2:f0:\n-47:69:e4\n+17:39:e6\n %0A   \n@@ -1883,15 +1883,15 @@\n dr:1\n-00\n+21\n .15.\n-2\n+1\n 8.4 \n@@ -1957,27 +1957,27 @@\n  fe2\n-0::7c72:f0f\n+1::7d74:f0d\n f:fe17:\n-6\n+4\n 4e4/\n@@ -2442,17 +2442,17 @@\n   MTU:65\n-5\n+2\n 36  Metr\n@@ -3087,16 +3087,17 @@\n addr: 10\n-\n+1\n .5.7.40%60\n@@ -4820,25 +4820,26 @@\n %60%60%0Aping \n-votatu.es\n+lemonde.fr\n  -c 5%0A%60%60\n@@ -4891,17 +4891,11 @@\n now \n-votatu.es\n+.fr\n  is \n@@ -5536,9 +5536,148 @@\n **Dos**)\n-\n+.%0A%0AWhat else can we find about a server? Let's find out in %5B%5BPart 15%5D(https://steemit.com/linux/@alphydan/teaching-cyber-security-part-15)%5D\n .\n",
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      "parent_permlink": "linux",
      "author": "alphydan",
      "permlink": "teaching-cyber-security-part-13",
      "title": "Teaching Cyber Security (Part 13)",
      "body": "@@ -77,17 +77,17 @@\n ub. Read\n-%0A\n+ \n %5B%5Bpart 1\n@@ -304,16 +304,17 @@\n opefully\n+,\n  it work\n@@ -315,17 +315,17 @@\n t worked\n-,\n+.\n  Let's t\n@@ -794,17 +794,18 @@\n we learn\n-t\n+ed\n %0A%0AWe hav\n@@ -811,17 +811,18 @@\n ve learn\n-t\n+ed\n  lots of\n@@ -2038,12 +2038,106 @@\n vers online.\n+ Let's go to %5B%5BPart 14%5D(https://steemit.com/linux/@alphydan/teaching-cyber-security-part-14)%5D.\n",
      "json_metadata": "{\"tags\":[\"linux\",\"bash\",\"security\",\"teaching\",\"coding-club\"],\"links\":[\"https://steemit.com/linux/@alphydan/teaching-cyber-security-part-12\",\"https://steemit.com/linux/@alphydan/teaching-cyber-security-part-14\"],\"app\":\"steemit/0.1\",\"format\":\"markdown\"}"
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      "permlink": "teaching-cyber-security-part-12",
      "title": "Teaching Cyber Security (Part 12)",
      "body": "@@ -77,17 +77,17 @@\n ub. Read\n-%0A\n+ \n %5B%5Bpart 1\n@@ -268,53 +268,24 @@\n nds \n-decreases the time we expend removing,\n+allow us to\n  mov\n-ing\n+e\n  and\n@@ -290,19 +290,17 @@\n nd renam\n-ing\n+e\n  files a\n@@ -371,18 +371,18 @@\n  them?__\n-%0A%0A\n+  \n Yes it i\n@@ -383,16 +383,19 @@\n s it is!\n+ %F0%9F%98%84\n %0A%0A### In\n@@ -403,17 +403,16 @@\n roducing\n-:\n  the %60cp\n@@ -1457,24 +1457,114 @@\n s well.%0A%0A###\n+ !%5B%5D(https://steemitimages.com/DQmPu53qcjmKZa7SVjKFgN6kuHxuipUq4CoCx56kYBt4Gvm/image.png) \n  Command:%0A%60%60\n@@ -1560,21 +1560,18 @@\n Command:\n-%0A%60%60%60%0A\n+ %60\n cp %3Copti\n@@ -1596,21 +1596,21 @@\n ination%3E\n-%0A%60%60%60%0A\n+%60%0A%0A%3E \n __Defini\n@@ -1612,25 +1612,25 @@\n efinition:__\n-%0A\n+ \n The %60cp%60 com\n@@ -2498,29 +2498,131 @@\n ### \n-Command: %0A%60%60%60%0Arm%0A%60%60%60%0A\n+!%5Bbrain to remember%5D(https://steemitimages.com/DQmPu53qcjmKZa7SVjKFgN6kuHxuipUq4CoCx56kYBt4Gvm/image.png) Command:  %60rm%60%0A%3E \n __De\n@@ -2632,17 +2632,17 @@\n ition:__\n-%0A\n+ \n The %60rm%60\n@@ -3314,18 +3314,85 @@\n  in \n-the next part\n+%5B%5BPart 13%5D(https://steemit.com/linux/@alphydan/teaching-cyber-security-part-13)%5D\n .\n",
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      "parent_permlink": "linux",
      "author": "alphydan",
      "permlink": "teaching-cyber-security-part-11",
      "title": "Teaching Cyber Security (Part 11)",
      "body": "@@ -77,17 +77,17 @@\n ub. Read\n-%0A\n+ \n %5B%5Bpart 1\n@@ -158,16 +158,17 @@\n art-10)%5D\n+.\n %0A%0A%0A# Pip\n@@ -1278,28 +1278,651 @@\n %0A%0A# \n-Dictionary challenge\n+!%5BChallenge Question%5D(https://steemitimages.com/DQmfPjYtZNchP2w2jwNT9x8YbTrFACDWxUBRVGXVjz1oXnv/question-45px.png) Dictionary challenge%0A%0A**Can you find out how many words are in the American English dictionary?**%0AAnother way to phrase it is: Can you use a pipe %60%7C%60 to count the words inside the file %60american-english%60?%0A%0ARemember that you may need to move to %60/usr/share/dict/%60 to find the file.  Also remember that %60cat%60 prints out the content of the file, one line per word. Feel free to go back to %5B%5Bpart 10%5D(https://steemit.com/linux/@alphydan/teaching-cyber-security-part-10)%5D to review the syntax of the pipe operator.%0A%0A%3E Did you manage?\n %0A%0A# \n@@ -2625,16 +2625,19 @@\n means:  \n+%0A%3E \n print al\n@@ -2938,18 +2938,16 @@\n onary?  \n-%0A%0A\n Can you \n@@ -3079,8 +3079,132 @@\n kers do!\n+ %0ALet's learn a few more useful commands in %5B%5BPart 12%5D(https://steemit.com/linux/@alphydan/teaching-cyber-security-part-12)%5D\n",
      "json_metadata": "{\"tags\":[\"linux\",\"bash\",\"security\",\"teaching\",\"coding-club\"],\"links\":[\"https://steemit.com/linux/@alphydan/teaching-cyber-security-part-10\",\"https://steemit.com/linux/@alphydan/teaching-cyber-security-part-12\"],\"app\":\"steemit/0.1\",\"format\":\"markdown\",\"image\":[\"https://steemitimages.com/DQmfPjYtZNchP2w2jwNT9x8YbTrFACDWxUBRVGXVjz1oXnv/question-45px.png\"]}"
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      "permlink": "teaching-cyber-security-part-10",
      "title": "Teaching Cyber Security (Part 10)",
      "body": "@@ -5297,14 +5297,9 @@\n s?  \n-Read m\n+M\n ore \n",
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      "parent_permlink": "linux",
      "author": "alphydan",
      "permlink": "teaching-cyber-security-part-10",
      "title": "Teaching Cyber Security (Part 10)",
      "body": "@@ -77,17 +77,17 @@\n ub. Read\n-%0A\n+ \n %5B%5Bpart 9\n@@ -156,17 +156,17 @@\n part-9)%5D\n-%0A\n+.\n %0A%0A# Pipe\n@@ -2882,29 +2882,135 @@\n ### \n-Command: %0A%60%60%60%0Awc%0A%60%60%60%0A\n+!%5Bbrain to remember%5D(https://steemitimages.com/DQmYzciN7JfVYD7XwHrKWAtUNgjVeXbsQACDB5YSxhVMb1i/Brain-60px.png) Command: %60wc%60%0A%3E \n __De\n@@ -3717,16 +3717,129 @@\n .  %0A%0A###\n+  !%5Bbrain to remember%5D(https://steemitimages.com/DQmYzciN7JfVYD7XwHrKWAtUNgjVeXbsQACDB5YSxhVMb1i/Brain-60px.png) \n  Command\n@@ -3840,21 +3840,18 @@\n ommand: \n-%0A%60%60%60%0A\n+ %60\n %3Cinput%3E \n@@ -3860,21 +3860,21 @@\n %3Coutput%3E\n-%0A%60%60%60%0A\n+%60%0A%0A%3E \n __Defini\n@@ -5222,13 +5222,173 @@\n through sshd\n-%60\n+ right now%60%0A%0ABut how can we use pipes for security and passwords?  Read more in %5B%5BPart 11%5D(https://steemit.com/linux/@alphydan/teaching-cyber-security-part-11)%5D.\n",
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      "permlink": "teaching-cyber-security-part-9",
      "title": "Teaching Cyber Security (Part 9)",
      "body": "@@ -76,17 +76,17 @@\n ub. Read\n-%0A\n+ \n %5B%5Bpart 8\n@@ -314,24 +314,134 @@\n idying.%0A%0A###\n+ !%5Bbrain definition%5D(https://steemitimages.com/DQmYzciN7JfVYD7XwHrKWAtUNgjVeXbsQACDB5YSxhVMb1i/Brain-60px.png)\n  Command: %0A%60\n@@ -438,21 +438,18 @@\n ommand: \n-%0A%60%60%60%0A\n+ %60\n mkdir NA\n@@ -461,21 +461,21 @@\n _NEW_DIR\n-%0A%60%60%60%0A\n+%60%0A%0A%3E \n __Defini\n@@ -477,25 +477,25 @@\n efinition:__\n-%0A\n+ \n The %60mkdir%60 \n@@ -736,16 +736,27 @@\n mystuff%60\n+ by typing:\n %0A%0A    mk\n@@ -871,90 +871,141 @@\n ay. \n-Let's take that there's an %60untidy%60 file to be moved.%0A%0A### Command: %0A%60%60%60%0Amv untidy\n+%0A%0A### !%5Bbrain definition%5D(https://steemitimages.com/DQmYzciN7JfVYD7XwHrKWAtUNgjVeXbsQACDB5YSxhVMb1i/Brain-60px.png) Command: %60mv file\n  dir\n@@ -1010,21 +1010,21 @@\n irectory\n-%0A%60%60%60%0A\n+%60%0A%0A%3E \n __Defini\n@@ -1030,17 +1030,17 @@\n ition:__\n-%0A\n+ \n The %60mv%60\n@@ -1220,29 +1220,22 @@\n ut. \n-Figure out now\n+Assume\n  there\n-'\n+ i\n s a \n@@ -2166,8 +2166,133 @@\n bsite/%60.\n-\n \n+%0A%0ALet's move on to more advanced commands in %5B%5BPart 10%5D(https://steemit.com/linux/@alphydan/teaching-cyber-security-part-10)%5D\n",
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  "op": [
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      "permlink": "teaching-cyber-security-part-8",
      "title": "Teaching Cyber Security (Part 8)",
      "body": "@@ -76,17 +76,17 @@\n ub. Read\n-%0A\n+ \n %5B%5Bpart 7\n@@ -1044,16 +1044,147 @@\n s.%0A%0A### \n-\n \n+!%5Binfo%5D(https://steemitimages.com/0x0/https://steemitimages.com/DQmfPjYtZNchP2w2jwNT9x8YbTrFACDWxUBRVGXVjz1oXnv/question-45px.png) \n Using th\n@@ -2134,78 +2134,206 @@\n . %0A%0A\n-Press the __up/down arrow keys__ for going through the command history\n+!%5Binfo%5D(https://steemitimages.com/0x0/https://steemitimages.com/DQmfPjYtZNchP2w2jwNT9x8YbTrFACDWxUBRVGXVjz1oXnv/question-45px.png) Press the __up/down arrow keys__ to get the last commands you typed\n :%0A%0A!\n@@ -2454,12 +2454,122 @@\n history.gif)\n+%0A%0ATo continue this course, Read %5B%5BPart 9%5D(https://steemit.com/linux/@alphydan/teaching-cyber-security-part-9)%5D\n",
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      "permlink": "teaching-cyber-security-part-7",
      "title": "Teaching Cyber Security (Part 7)",
      "body": "@@ -3601,31 +3601,162 @@\n ### \n-Command: %0A%60%60%60%0A\n+!%5Bcommand icon%5D(https://steemitimages.com/0x0/https://steemitimages.com/DQmYzciN7JfVYD7XwHrKWAtUNgjVeXbsQACDB5YSxhVMb1i/Brain-60px.png) Command %60\n clear\n-%0A%60%60%60\n+%60: %0A\n %0A__D\n",
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      "body": "Continue reading [Part 7](https://steemit.com/linux/@alphydan/teaching-cyber-security-part-7) of this course here: https://steemit.com/linux/@alphydan/teaching-cyber-security-part-7",
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  "timestamp": "2018-02-13T00:27:03",
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      "parent_permlink": "linux",
      "author": "alphydan",
      "permlink": "teaching-cyber-security-part-7",
      "title": "Teaching Cyber Security (Part 7)",
      "body": "@@ -76,17 +76,17 @@\n ub. Read\n-%0A\n+ \n %5B%5Bpart 6\n@@ -163,16 +163,17 @@\n part-6)%5D\n+.\n %0A%0A# Hack\n@@ -283,26 +283,33 @@\n ty**:%0A!%5B\n-datacenter\n+server_in_holland\n .jpg%5D(ht\n@@ -339,63 +339,70 @@\n /DQm\n-e3vtMxbteZFRS9kpyUTY5RF9oYfgNCQbauw7X5p8aNnR/datacenter\n+SWGn3JLhQwWK45hLeLd7YRfGCU4eAfSM6duMFiwCbCeG/server_in_holland\n .jpg\n@@ -1480,16 +1480,19 @@\n  usually\n+:%0A%3E\n  go on t\n@@ -3558,16 +3558,48 @@\n top.png)\n+%0ASource: https://hisham.hm/htop/\n %0A%0ABefore\n",
      "json_metadata": "{\"tags\":[\"linux\",\"bash\",\"security\",\"teaching\",\"coding-club\"],\"image\":[\"https://steemitimages.com/DQmSWGn3JLhQwWK45hLeLd7YRfGCU4eAfSM6duMFiwCbCeG/server_in_holland.jpg\",\"https://steemitimages.com/DQmYfQS5PqKo626CkwcwmvyhZbBz9qggSNjLWkEQHMvjz5s/shell_htop.png\"],\"links\":[\"https://steemit.com/cybersecurity/@alphydan/teaching-cyber-security-part-6\",\"https://hisham.hm/htop/\",\"https://steemit.com/linux/@alphydan/teaching-cyber-security-part-8\"],\"app\":\"steemit/0.1\",\"format\":\"markdown\"}"
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      "author": "security101",
      "permlink": "re-alphydan-re-security101-re-alphydan-teaching-cyber-security-part-7-20180212t005323886z",
      "title": "",
      "body": "Oh i have not. Sorry about that. \nKeep up your great work ! :)",
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      "author": "steemitboard",
      "permlink": "steemitboard-notify-alphydan-20180211t222620000z",
      "title": "",
      "body": "Congratulations @alphydan! You have completed some achievement on Steemit and have been rewarded with new badge(s) :\n\n[![](https://steemitimages.com/70x80/http://steemitboard.com/notifications/posts.png)](http://steemitboard.com/@alphydan) Award for the number of posts published\n\nClick on any badge to view your own Board of Honor on SteemitBoard.\nFor more information about SteemitBoard, click [here](https://steemit.com/@steemitboard)\n\nIf you no longer want to receive notifications, reply to this comment with the word `STOP`\n\n> By upvoting this notification, you can help all Steemit users. Learn how [here](https://steemit.com/steemitboard/@steemitboard/http-i-cubeupload-com-7ciqeo-png)!",
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      "parent_permlink": "cibersecurity",
      "author": "alphydan",
      "permlink": "teaching-cyber-security-unit2-part3",
      "title": "Teaching Cyber Security (Part17)",
      "body": "@@ -77,17 +77,17 @@\n ub. Read\n-%0A\n+ \n %5B%5Bpart 1\n",
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      "permlink": "teaching-cyber-security-unit2-part3",
      "title": "Teaching Cyber Security (Part17)",
      "body": "@@ -1,8 +1,175 @@\n+This is the 17th post of a series for teaching cyber-security in a coding-club. Read%0A%5B%5Bpart 16%5D(https://steemit.com/linux/@alphydan/teaching-cyber-security-part-16)%5D%0A%0A\n # Puttin\n@@ -187,16 +187,17 @@\n gether%0A%0A\n+#\n # Combin\n@@ -207,16 +207,16 @@\n  it all%0A\n-\n In this \n@@ -360,16 +360,17 @@\n ssion!%0A%0A\n+#\n # Findin\n",
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      "title": "Teaching Cyber Security (Part 16)",
      "body": "This is the 16th post of a series for teaching cyber-security in a coding-club. Read\n[[part 15](https://steemit.com/linux/@alphydan/teaching-cyber-security-part-15)]\n\n\n\n# Bash scripts\n\n# The Shell\n\nWelcome to Module 2, Unit 2.  By now you should be familiar with the operation of the shell (and the programs which run on it using the Bash language).\n\nYou can thank Brian Fox for creating the `shell` and sharing it freely with the world. \n ![brian-fox.png](https://steemitimages.com/DQmZRnJbmXWAjvTtTAfAjaTQbePJv4CiNEykVbXmB1GX8so/brian-fox.png) Brian Fox\nTogether with other computer scientists they started a movement called Free Software where anybody in the world could copy, modify and use their creations.  Today, most computers in the world (the ones called servers which make websites possible) are powered by their tools.  Free software is different from Microsoft Windows in that you can look \"under the hood\" and find out what it is doing. Here's another amazing coder who also creates and promotes free software:\n![allison_randal_coder_small.png](https://steemitimages.com/DQmeHVjx7RSBmguaKb1iUjgvFcNDyn8oXmMrBX9vEnCHfi3/allison_randal_coder_small.png)\n[Allison Randal](https://allisonrandal.com/)\n\n## Combining shell commands\n\nNow let's get back to business. You need to go inside our secret .  To do that you need to find the IP address of the server, and `ssh` into it. At this point you should understand what the previous sentence means.\n\nTo do this you need to know the user and password.  Now, `admin` is a very common user, so that would be a good thing to try.\n\n```\nssh [email protected]\n```\nWhere `X.X.X.X` would be the numbers for the IP address. Once you try that it would ask:\n```\[email protected]'s password: ________________\n```\nAnd you could try \"hello1\".  If it doesn't work you would have to `ssh` again and try something new like \"rabbits33\" or \"asdf;lkj\".  However there are hundreds of thousands of combinations!  It would take forever to try all of them by hand.\n\n>So what can we do?\n\nWe need to write a short shell program to do things for us.\n\n\n# Loops\n\n## Doing something 10,000 times!\n\nLet's think about how we could try different combinations. Let's start with a simpler problem:  Can we get the shell to print the numbers 1 to 10? In other words, can we get:\n```\n$ 1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n```\n\nWell, you could type each and every number, but that would not be fun if we had to print 1 → 10,000. \n\n## for loops\n\nTo tackle this problem the Bash language (and many other programming languages) has something called loops.  It's a procedure which gets repeated over and over with a little change each time.\n\nOur procedure looks something like this:\n\n`x = 1`\n`print x`\n\nnow change `x = 1` to `x = 2`\n`print x`\n\nnow change `x = 2` to `x = 3`\n`print x`\n\nand so on.\n\nBash has a special way to write this.  The syntax is the following:\n\n```\nfor x in {1..10}\n```\n\nwhich means:\n- consider that x is the first element of the list {**1**,2,3,4,5,6,7,8,9,10}. \nThen \n- consider that x is the second element of the list {1,**2**,3,4,5,6,7,8,9,10}\nThen\n- consider that x is the third element of the list {1,2,**3**,4,5,6,7,8,9,10}\n\n- ... And so on until:\n- consider that x is the last element of the list {1,2,3,4,5,6,7,8,9,**10**}\n\nNow, for each value of x you can make the computer **do something**.  Let's start with something very easy called `echo` which means `print it to the shell`.  Our loop is going to be:\n\n```\nfor x in {1..10}\ndo\n  echo $x\ndone\n```\n\nWhich means:\n- first x is 1, so do `echo x`\n- then x is 2, so do `echo x`\n- then x is 3, so do `echo x`\n- etc\n\nGo ahead and type those lines in the shell. You can type one line after another, or you can separate them with semicolons:\n\n```\nfor x in {1..10}; do echo $x; done\n```\n\nDid it work? Can you print the first 10,000 numbers to the shell?",
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