Share Published on Jun 13, 2014 Engineering Technology Economy & Finance 2 Comments Statistics Notes Show More Views Actions 0 Embeds 0 1.Presented By: Wajid Ali Hamdani (232) Department Of Computer Science and Engineering 2.CONTENTS:  Abstract  Overview  History  Security  References 3.Abstract:  Bitcoin is a peer-to-peer payment system introduced as open- source software in 2009 by developer Satoshi Nakamoto. The payments in the system are recorded in a public ledger using its own unit of account, which is also called bitcoin. The bitcoin system has no central repository and no single administrator, which has led the US Treasury to call bitcoin a decentralized virtual currency. Although its status as a currency is disputed, media reports often refer to bitcoin as a crypto currency or digital currency. Bitcoins are created as a reward for payment processing work in which users offer their computing power to verify and record payments into the public ledger.

Called mining, individuals or companies engage in this activity in exchange for transaction fees and newly created bitcoins. Besides mining, bitcoins can be obtained in exchange for fiat money, products, and services.change litecoin to euro Users can send and receive bitcoins electronically for an optional transaction fee using wallet software on a personal computer, mobile device, or a web application.bitcoin australia atmOverview:  The most important part of the bitcoin system is a public ledger that records financial transactions in bitcoins.free bitcoin paga Recording transactions is accomplished without the intermediation of any single, central authority.boutique bitcoin paris

 Instead, multiple intermediaries exist in the form of computer servers running bitcoin software.By connecting over the Internet, these servers form a network that anyone can join.bitcoin nyse tickerTransactions of the form payer X wants to send Y bitcoins to payee Z, are broadcast to this network using readily available software applications.5 gh/s bitcoin miner kaufenBitcoin servers can validate these transactions, add them to their copy of the ledger, and then broadcast these ledger additions to other servers.bitcoin technology slideshareHistory:  Bitcoin was first mentioned in a 2008 research paper published under the name Satoshi Nakamoto.1 gh bitcoin miner

 Some mainstream websites began accepting bitcoins 2013.WordPress started in November 2012 followed by OKCupid in April 2013, Atomic Mall in November 2013, that same month.bitcoin replace by fee In October 2013, Chinese internet giant Baidu had allowed clients of website security services to pay with bitcoins.During November 2013, the China-based bitcoin exchange BTC China overtook the Japan-based Mt.Gox and the Europe-based Bitstamp to become the largest bitcoin trading exchange by trade volume. The first bitcoin ATM was installed in October 2013 in Vancouver, British Columbia, Canada.Security:  There are two main ways the block chain ledger can be corrupted to steal bitcoins: by fraudulently adding to or modifying it.The bitcoin system protects the blockchain against both using a combination of digital signatures and cryptographic hashes.

 The Addition Attack and Digital Signatures:  Payers and payees are identified in the blockchain by their public cryptographic keys: most bitcoin transfers are from one public key to a different public key. The Modification Attack And Mining:  The other principal way to steal bitcoins would be to modify blockchain ledger entries.Eve could buy something from Alice, like a sofa, by adding a signed entry to the blockchain ledger equivalent to Eve pays Alice 100 bitcoins.Later, after receiving the sofa, Eve could modify that blockchain ledger entry to read instead: Eve pays Alice 1 bitcoin, or even delete the entry.Digital signatures cannot prevent this attack: Eve can simply sign her entry again after modifying it.References:  Ron Dorit; Adi Shamir (2012)."Quantitative Analysis of the Full Bitcoin Transaction Graph".Retrieved 18 October 2012. "Cracking the Bitcoin: Digging Into a $131M USD Virtual Currency".Archived from the original on 20 January 2013.

Retrieved 30 September 2012. Jon Matonis (17 September 2013)."Bitcoin gaining market-based legitimacy as XBT".Retrieved 14 December 2013. "Bitcoin: A Peer-to-Peer Electronic Cash System".Retrieved 28 April 2014. "Regulation of Bitcoin in Selected Jurisdictions".The Law Library of Congress, Global Legal Research Center.Retrieved 9 April 2014. Bustillos, Maria (2 April 2013).Retrieved 22 December 2013."(Standards vary, but there seems to be a consensus forming around Bitcoin, capitalized, for the system, the software, and the network it runs on, and bitcoin, lowercase, for the currency itself.)" 9.Share Published on Nov 16, 2016 The blockchain and blockchain related topics are becoming increasingly discussed and studied nowadays.There is not one single day where I don't hear about it, that being on linkedin or elsewhere.I interested myself deeply in the blockchain topic recently and this is the first article of a coming whole serie around the blockchain.

This presentation is an introduction to the blockchain, presents what it is in the light of its initial deployment in the Bitcoin project as well as all technical details and architecture concerns behind it.We won't focus here on business applications aside from what is required to present the blockchain purpose, more concrete business applications and evolutions will be the topic of another presentation I'll post in a few weeks ... Technology 8 Comments Statistics Notes Show More Views Actions 0 Embeds 0 1.1 © Jerome Kehrli @ niceideas.ch http://www.niceideas.ch/roller2/badtrash/entry/blockchain-explained-beta The Blockchain The Technology behind Bitcoin 2.What is the blockchain ?3 INITIAL DEFINITION The blockchain is the technology running the bitcoin.Some Definitions WIKIPEDIA DEFINITION A blockchain is a distributed database that maintains a continuously- growing list of records called blocks secured from tampering and revision.

MY DEFINITION The blockchain is a secured protocol enabling peer-to-peer exchanges on a distributed network in a secured, public and non-repudiable way.4 A tiny little bit of history Architecture and principle first designed for Bitcoin A solution to make the database both secured and widely distributed Actually the main innovation of the Bitcoin Conceived in 2008 and implemented in 2009 Satoshi Nakamoto As of 2014 : “Blockchain 2.0” Evolution over the initial blockchain From simple transactions to actual Software Programs From simply a distributed transaction ledger to a globally decentralized, un- ownable, digital computer 5.5 Introduction Example Bob is an online web surfer and is looking for a suite.He wants to buy it online.Sally runs an online shop and sells clothes.Problem(s) solved by the blockchain 7.7 Usual Situation (1) Recall the introduction problem This is what happens in practice 8.

8 Usual Situation (2) 9.9 Usual Situation (3) 10.10 Usual Situation (4) 11.11 Usual Situation (5) 12.12 Usual Situation (6) 13.13 Usual Situation (7) 14.14 Usual Situation (8) 15.15 The financial system is opaque and lacks transparency and fairness.All these intermediates are no volunteers.They work for money and get paid for their services.The transaction costs money to both the buyer and the seller.There are interest rates, fees, surcharges, etc. EFTs in Europe can cost 25 euros.Credit transactions can cost several percent of the transaction.All these exchanges are error prone.Credit card informations are often stolen.An account holder is eventually not even the actual owner of his account.The bank really owns the account.Funds can be garnished, even frozen completely.Banks and other payment processors like PayPal, Visa, and Mastercard may refuse to process payments for certain legal entities.Financial exchanges are slow.

Checking and low cost wire services take days to complete.The problems with this model 16.16 A clearing house is a financial institution that provides clearing and settlement services for financial and commodities derivatives and securities transactions stands between two clearing participants / firms (banks) reduces the risk of one (or more) clearing firm failing to honor its trade settlement obligations.It nets offsetting transactions between multiple counterparties.17 Clearing House (1) Buyers and sellers use intermediaries because they may not trust the other party, but they trust that the intermediary will assure the transaction is completed faithfully.This is the fundamental role of a clearing house 18.18 Clearing House (2) 19.19 When one bank sends money to another, no physical currency changes hands.Banks and settlement systems use central electronic ledgers to track assets.But such central ledgers - or clearing houses - can be slow and inefficient, often relying on faxes or manual input.

That not only wastes time but racks up fees.The system is also open to hacking and fraud.These central institutions gets fees to cover such risks of course as well as many other services.The price is high It prevents, for instance, micro-payments services who are not able to support the charge asked by these central structures.The problems with Clearing Houses 20.20 Distributed Ledgers OTHER DEFINITION A blockchain is a type of distributed ledger, comprised of unchangeable, digitally recorded data in packages called blocks.A distributed ledger (also called shared ledger) is a consensus of replicated, shared, and synchronized digital data geographically spread across multiple sites, countries, and/or institutions.Every node in the decentralized system has a copy of the ledger.No centralized "official" copy exists and no user is "trusted" more than any other.21 Distributed Ledger instead of Central Ledger 22.Operation of the blockchain 23.

23 Blockchain overview (1) The blockchain itself is a list of blocks.These digitally recorded "blocks" of data are stored in a linear chain.Each block in the chain contains data (e.g.bitcoin transaction) and is cryptographically hashed.Each block includes the hash of the prior block in the blockchain, linking the two, ensuring all data in the overall "blockchain" has not been tampered with and remains unchanged.This has the effect of creating a chain of blocks from the genesis block to the current block.Each block is guaranteed to come after the previous block chronologically because the previous block's hash would otherwise not be known.24 Blockchain overview (2) The blockchain network is a peer-to-peer network of independent nodes communicating together by message broadcasting.A node is not necessarily connected to every other node, but at least some of them.25 Blockchain overview (3) 26.26 Blockchain principle (1) The operation principle of is pretty straightforward to understand.

We’ll illustrate it her on the Bitcoin blockchain.Principle is as follows : 1.A user wants to pay another user some bitcoins, he broadcasts a transaction to the network.Miners add the transaction as they receive it to their current block, the one they are currently working on 3.Randomly, one of the miner may win the lottery and "mine" the block (we'll get back to that) 4.At that moment, this new "definitive" block is broadcasted to the network and added to everyone's copy of the blockchain 27.27 Blockchain principle (2) 28.28 Blockchain principle (3) 29.29 Blockchain principle (2) 30.30 Blockchain principle (2) 31.31 Blockchain principle (2) 32.32 In order for a block to be accepted by network participants, miners must complete a proof of work which covers all of the data in the block.The proof of work is a piece of data which is difficult (costly, time-consuming) to produce but easy for others to verify and which satisfies certain requirements.

Producing a proof of work can be a random process with low probability so that a lot of trial and error is required on average before a valid proof of work is generated.Bitcoin uses the Hashcash proof of work system.For a block to be valid it must hash to a value less than the current target; this means that each block indicates that work has been done generating it.Each block contains the hash of the preceding block, thus each block has a chain of blocks that together contain a large amount of work.Changing a block (which can only be done by making a new block containing the same predecessor) requires regenerating all successors and redoing the work they contain.This protects the block chain from tampering.The amount of successors is relevant when qualifying the validity of a block : at least 6 successors are required to consider a block valid Proof of Work 33.33 Mining principle (1) 34.34 Mining principle (2) 35.35 Mining principle (3) 36.

36 Mining principle (4) 37.37 Mining principle (5) 38.39 Blockchain structure The blockchain data structure is an ordered, back-linked list of blocks of transactions.Every block contains a hash of the previous block.This has the effect of creating a chain of blocks from the genesis block to the current block.Each block is also computationally impractical to modify once it has been in the chain for a while because every block after it would also have to be regenerated.New transactions are constantly being processes by miners into new blocks which are added to the end of the chain and can never be changed or removed once accepted by the network.40 Block Structure Each block contains, among other things : a record of some or all recent transactions, and a reference to the block that came immediately before it.It also contains an answer to a difficult-to- solve mathematical puzzle, the hash or Proof of Work.

41 Mining In the Bitcoin world, transactions are broadcast to the network by the sender, and all peers trying to solve blocks collect the transaction records and add them to the block they are working to solve.This is called Mining.Mining is the process of adding transaction records to Bitcoin's public ledger of past transactions.This ledger of past transactions is called the block chain as it is a chain of blocks.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.The primary purpose of mining is to allow Bitcoin nodes to reach a secure, tamper-resistant consensus.42 Mining algorithm (1) 43.43 Mining algorithm (2) 44.44 Mining algorithm (3) 45.45 Mining algorithm (4) 46.46 Mining algorithm (5) 47.47 Mining algorithm (6) 48.48 Mining algorithm (7) 49.

49 Mining algorithm (8) 50.50 The difficulty is the measure of how difficult it is to find a new block compared to the easiest it can ever be.It is recalculated every 2016 blocks to a value such that the previous 2016 blocks would have been generated in exactly two weeks had everyone been mining at this difficulty.This will yield, on average, one block every ten minutes.51 Target Value (1) 52.52 Target Value (2) 53.53 Target Value (3) 54.54 Target Value (4) 55.55 Target Value (5) 56.56 Target Value (6) 57.57 Target Value (7) 58.58 Target Value (8) 59.59 Mining is also the mechanism used to introduce Bitcoins into the system: Miners are paid any transaction fees as well as a "subsidy" of newly created coins.These both serves the purpose of disseminating new coins in a decentralized manner as well as motivating people to provide security for the system.It gives miners incentive to put their computation power at the disposal of the blockchain network.

Because there is a reward of brand new bitcoins for solving each block, every block also contains a record of which Bitcoin addresses or scripts are entitled to receive the reward.This record is known as a generation transaction (or a coinbase transaction) and is always the first transaction appearing in every block.60 Miner’s reward (1) 61.61 Miner’s reward (2) 62.62 Miner’s reward (3) 63.63 Miner’s reward (4) 64.64 In the specific case of the bitcoin, Satoshi had very soon the idea of limiting the bitcoin supply.In a centralized economy, currency is issued by a central bank at a rate that is supposed to match the growth of the amount of goods that are exchanged so that these goods can be traded with stable prices.The monetary base is controlled by this central bank.In the United States, the Fed increases the monetary base by issuing currency, increasing the amount banks have on reserve, and more recently, printing money electronically in a process called Quantitative Easing.

In a fully decentralized monetary system, there is no central authority that regulates the monetary base.Instead, currency is created by the nodes of a peer-to-peer network.The Bitcoin generation algorithm defines, in advance, how currency will be created and at what rate.Any currency that is generated by a malicious user that does not follow the rules will be rejected by the network and thus is worthless.Bitcoins are created each time a user discovers a new block.The rate of block creation is adjusted every 2016 blocks to aim for a constant two week adjustment period (equivalent to 6 per hour.)The number of bitcoins generated per block is set to decrease geometrically, with a 50% reduction every 210,000 blocks, or approximately four years.The result is that the number of bitcoins in existence is not expected to exceed 21 million.Speculated justifications for the unintuitive value "21 million" are that it matches a 4-year reward halving schedule; or the ultimate total number of bitcoins that will be mined is close to the maximum capacity of a 64-bit floating point number.

Bitcoin limited supply 65.65 Bitcoin Monetary Inflation 66.66 A wallet is basically the Bitcoin equivalent of a bank account.It allows you to receive bitcoins, store them, and then send them to others.The name "Bitcoin wallet" is a bit of a misnomer.Bitcoin wallets don't hold actual Bitcoins, those are essentially stored on the blockchain.Instead, Bitcoin wallets hold the private keys that give users the right to use those coins.Each Bitcoin wallet comes with at least two keys : one public, and one private.A Bitcoin address, or simply address, is an identifier of 26-35 alphanumeric characters, beginning with the number 1 or 3, that represents a possible destination for a bitcoin payment.Addresses can be generated at no cost by any user of Bitcoin.Bitcoin Wallet Cryptography 67.67 Wallet cryptography (1) 68.68 Wallet cryptography (2) 69.69 Wallet cryptography (3) 70.70 Wallet cryptography (4) 71.71 A Merkle Tree is a tree constructed by hashing paired data (the leaves), then pairing and hashing the results until a single hash remains, the merkle root.

The construction of the Merke tree is such that if any single leaf transaction is changed, all hashes along the branch would be changed and ultimately the merkle root as well.This is a key property ensuring security of the blockchain.Merkle trees in bitcoin use a double SHA-256, the SHA-256 hash of the SHA- 256 hash of something.72 Merkle Tree This procedure repeats recursively until we reach a row consisting of just a single double-hash.This is the Merkle root of the tree.First from the top row of the tree with the ordered double-SHA- 256 hashes of the byte streams of the transactions in the block.Then the row below it consists of half that number of hashes.Each entry is the double-SHA- 256 of the 64-byte concatenation of the corresponding two hashes below it in the tree.73 Replication (1) Both new transactions and newly mined blocked are broadcasted to the peer-to- peer network using the Flood Protocol.

74 Replication (2) 75.75 Replication (3) 76.76 Replication (4) 77.77 Replication (5) 78.78 Replication (6) 79.79 It's possible for the blockchain to have temporary splits for instance, if two miners arrive at two different valid solutions for the same block at the same time, unbeknownst to one another.The peer-to-peer network is designed to resolve these splits within a short period of time, so that eventually only one branch of the chain survives.The client accepts the longest chain of blocks as valid.The "length" of the entire block chain refers to the chain with the most combined difficulty, not the one with the most blocks.This prevents someone from forking the chain and creating a large number of low- difficulty blocks, and having it accepted by the network as "longest".Orphaned, Extinct and Staled Blocks 80.80 Blockchain branches(1) 81.81 Blockchain branches(2) 82.82 Blockchain branches(3) 83.

83 Blockchain branches(4) 84.84 Blockchain branches(5) 85.86 The Blockchain 2.0 is an evolution of the blockchain protocol enabling not only to exchange transaction but rather code and programs in the form of Smart Contracts Now developers are allowed to build programs and API's on the Blockchain Protocol.This relatively new concept involves the development of programs that can be entrusted with money.Smart contracts are programs that encode certain conditions and outcomes.By developing ready to use programs that function on predetermined conditions between the supplier and the client, smart programs ensure a secure escrow service in real time at near zero marginal cost Apart from Financial transactions, smart contracts makes the blockchain technology entering a whole lot of different industry.For instance in the Legal System, companies like Empowered Law use the public distributed ledger of transactions that makes up the Block Chain to provide Multi- Signature account services for asset protection, estate planning, dispute resolution, leasing and corporate governance.