part 1 : 태훈
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Hi, this is Kim Tae-hoon who is responsible for the Wanna One team's first presentation.
We make presentations with the topic of a block chain. Have you heard a lot?

###### *교재 p.34 기반 추가문*
> First, I will give you some information about cryptography such as Bitcoin and Ethereum.
Next, 경태 will introduce basic characters of blockchain.
Then, 병찬 is supposed to explain how blockchain works, in more detail way.
After that, 광현 is going to present his research on its future extension possibility.
Finally, 성환 close our presentation with letting you know what's happening now around the world.


Blockchain is a ~~technique~~ **technology** that prevents hackers from taking a break when dealing with cryptography.
So before I introduce this technology, I'll figure out what the cryptography ~~’s~~ mean**s**, how to use cryptography, and ~~what~~ kinds of cryptography.

First, cryptography is a kind of digital currency that is used in electronic form unlike paper money.
So, without government or central bank, it is possible to do fast and safe transactions with P2P method. *Total amount of money is limited like gold and it is created by using hash function for security.*

Second, bitcoin is popular example of cryptography.
Users create wallets with bitcoin addresses in their personal software, exchanges, and websites.
And make deals through this wallet.
The address of Bitcoin is a random string of English characters and numbers, ranging from 26 to 35 digits.

*QR code as well as direct address can be used as a mean for transaction of bitcoin.*
When you create a wallet, you do not need any personal information such as your name, phone number, or email address.

Third, we introduce two kinds of cryptography.
First, let me introduce ~~the~~ bit coin.
It is ~~the~~ world's first cryptography developed by Satoshi Nagamoto. Unofficial code is XBT or BTX.
The second is Etherium.
It was developed by a person named Vitalic Buterin. In 2013, we established the Etherium Foundation in London and formulated the business.
In 2014, he was named the IT Software winner of the World Technology Awards, out of Mark Zuckerberg.
In 2014, we approved the first exchange in New York, USA.
Before I finish the presentation, I think that cryptography are really something ~~to~~ **that will** change the landscape of finance.

*There is a kind of legendary funny story that someone just bought a hundred thousand won worth cryptography without serious thinking, but it became tens of millions of dollars.
I think being into it would be good because there will be lots of relations between computer science and blockchain.*

part 2 : 경태
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This time, I will introduce BlockChain to you with three step. I will thank you if you focus on my presentation.

First. What is the BlockChain?
Simply BlockChain is data distribution processing technology. In other words, it is technology that all users participating in network distribute or save data ~~all~~ about transaction record. This technology consist of blocks. *There is a structure named 'chain' between two distinct blocks and it connects blocks sequentially by following flow of time.* This is why this technology is named ‘BlockChain’.

Second. What is the difference?
In ~~existing~~ **traditional** transaction system, banks have all transaction history for proving ~~fact~~ **records** about transaction.
BlockChain also save*s* and prove*s* transaction record. But the transaction history is ~~divided~~ *distributed* by the number of people, not the bank.

Third. Character of BlockChain
~~The~~ BlockChain is characterized by distributed storage. Because of this character, ~~for many people save data (?)~~, forgery and modulation is too difficult! For forgery and modulation, hacker must attack ~~all~~ **more than half of all** participants’ data. So, virtually hacking is almost impossible.

Also, BlockChain is characterized by the absence of a central manager. The reason ~~the~~ central manager**s were** needed was formal vertification and authentication. But in BlockChain many people save and prove their data **one another**. So there is no need for central manager.

part 3 : 병찬
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Hi, this is 병찬 and I'm gonna illustrate how blockchain works. Basically, it is an abstract concept for decentralized record management, so specific principle should be different depending on platforms. However, it is possible to say that blockchain generally consists of these 5 core technologies, Peer-to-Peer network, digital sinature, hash function, consensus algorithm, and smart contract.
attacks, the harder he or she forge blocks because the attacker
As you might guessed, P2P networks enable us being free from middle institution for credibility.

And on the network, digital signiture is used to identify each person. Digital signiture is based on public and private key combination. Literally, public key is shared to public. And nobody knows private key except owner. Encrypted message with public key can be decoded by private key, and the opposite is also possible. So, if we encrypt transaction with our private key, others can decode it with our public key, so that they know it is really done by us.

And Next, one of the most impressive characteristics of blockchain is immutablity. If I say in more detail, this makes it more difficult to forge older record. This is possible by adapting hash. Hash function converts input string to certain complex string with fixed length. Even if the string just slightly changed, the output of hash function would be totally irrelvant. And one more curious character of hash is this : hash function is n to 1 function, so reverse function does not exist. So generating hash is so easy, but the opposite way is truly time-consuming.

Blockchain uses this trait when making chains of blocks. If you wanna make a block, you have to solve this kind of  time-consuming problem. The hash result will be given, and you should find a valid input for it, logically the reverse way hash function does. If someone try to forge record, as data changed, hashes to solve completely changed simultaneously as well. So the attacker cannot avoid calculating these problems again. As each blocks are 'chained' by hashes and solutions, the attacker who try to forge certain block have to change every following blocks, which means there are tons of hash calculation to be done. This is one of the core principle that makes blockchain so strong to forgery. And this mechanism is called 'consensus algorithm'. Of course, there are several kinds of consensus algorithm, such as PoW(Power of Work) or PoS(Power of Stake). But, the basic concepts are simmilar.

Finally, I'd like to introduce interesting and prosperous feature, 'smart contract'. Application rather than transaction can be the object of blockchain, so people can make smart contracts automatically executed on certain condition. Of course, this programmable contract is managed without 3rd party institution, and garantee 100% of credibility by all of us.


part 4 : 광현
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Hello I’m Kim-kwang-hyun, I am going to explain
about future possibility of Block chain.

As global chains of blockchain grows, *application of it is not emerging trend in international level.* National system development using block chain is active all over the world. At future, theoretically you can apply block-chain
technology to the registration, storage and trading of all kinds of assets.

And it can be also combined with other innovations in the era of the 4th Industrial Revolution. Therefore we expect to create new future services.

Here **are some** example**s** of future’s use of blockchain. The Internet **of Things** (IoT) and ~~the~~ blockchain are connected to each other to collect data such as road status quickly in real time through sensors in Smart City.
The driver checks this with a smartphone and they
can pay for parking space by bitcoin.

As you can see above, ~~The~~ block chain technology is **going to be** associated with most ICT technologies and will be used in all industries including financial and public industries in the future. So we have to modify the legal and institutional aspects of domestic blockchain.

part 5 : 성환
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This time, I will talk about the present of blockchain.

Block chain is springing up on these days. Now, ~~the~~ blockchain is the key to preventing hacking that can occur when trading with ~~virtual money~~ **cryptography**.

And advances in these capabilities have led to increased research**es** on expanding blockchain to non-virtualization sectors as well as virtual money services.

This can be used in many digital fields, such as game hacking prevention and protection of digital identities and so on.

But, there are still some gaps in connections with the block chain.

First, laws and regulations related to block chain are still in limbo. Because, it doesn’t fit well with the legislation applicable to banks. So, liability subject will become unclear in case of accidents or legal disputes.

Second, the market for blockchain is immature. Most of companies have won business acceptance levels and have not actually become commercialized in practice.

Third, there is insufficient work force involved in the blockchain. But, I think it will be solved soon with blockchain companies coming up.

I hope that many companies have ~~a~~ blockchain businesses and ~~do~~ **utilize** it actively. So, it can make our lives more comfortable and safe~~ly~~.

Thank you for listening.