openlab cryptocurrencies 20171006 final - crocs...• copycats – take bitcoin’s source code and...
TRANSCRIPT
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Petr Švenda
[email protected] @rngsec
Faculty of Informatics, Masaryk University, Czech Republic
OpenLab
Cryptocurrencies
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The plan
• Motivation and basics of Bitcoin operations
• Alternative cryptocoins to Bitcoin and why
• Make your own transaction
2 OpenLab: Cryptocurrencies
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APOLOGY FOR CZECH LANGSLIDES – NOC VĚDCŮ ☺(SEE ADDITIONAL SLIDES)
3 OpenLab: Cryptocurrencies
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• Ochrana soukromí
• Zaplacenou minci nelze použít znovu
Hotovostní platby
4 OpenLab: Cryptocurrencies
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Elektronická platby prostřednictvím banky
5 OpenLab: Cryptocurrencies
• Lze bezhotovostně a na „dálku“
• Co když Alice nemá účet u stejné banky?
• Co když banka začne podvádět?
4x $ 1x $
- 1$ + 1$
3x $
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Ideální elektronický převod a konto
• Rychlý převod (ideálně sekundy)
• Malé nebo žádné poplatky
• Soukromí (aby ostatní nevěděli, kolik máme)
• Nezávislost na centrální bance (hyper)-inflace
• Nemožnost padělat mince
• Snadné cestování s majetkem (ne kilogramy zlata ☺)
• …
6 OpenLab: Cryptocurrencies
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Digitální kryptografické měny - idea
1. Veřejná adresa a platební klíč (veřejný/privátní klíč)– Typicky 256b ECC
2. Kdo vlastní podepisovací klíč k adrese, ten může platit (provést transakci)
3. Veřejný seznam všech transakcí aby nešlo platit dvakrát (blockchain)
4. Náročný výpočet pro nový blok– Aby nebylo nutné mít centrální autoritu
7 OpenLab: Cryptocurrencies
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8 OpenLab: Cryptocurrencies
712.1 BTC 1.3 BTC
710.7 BTC
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• Jak zamezit dodatečné změně bloku s transakcemi?
• Digitální podpis nelze použít – nemáme banku
• Digitální těžaři (miners) se snaží vyřešit kvíz!
9 OpenLab: Cryptocurrencies
Číslo předchozího bloku
SHA256(blok) == ‘0000xxxxx’ ?
Náhodné semínko
Hash bloku (SHA256 )
12345
SHA256(blok)
93204
0000485739
3948023840
94302 0439391254
66439 5485498573
93204
…
0000485739
Semínko
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• Kdo první vyřeší kvíz, dostane 12.5 bitcoinů (฿)
• Navíc poplatky za zařazené transakce (+1฿)
Proč investovat energii do těžení?
10 OpenLab: Cryptocurrencies
13.42839934 ฿ == 57742 $ == 1.27 milionu Kč
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Jak rychle počítat hash SHA256?
11 OpenLab: Cryptocurrencies
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A těžaři počítají opravdu hodně!
• Počet hash za sekundu: 10 000 000 000 000 000– Zcela náhodné 8 znakové heslo by uhodli za 1 sekundu
– Správný blok nalezen jen jednou za 10 minut (těžké!)
• Spotřeba elektrické energie 18.4 TWh / rok– Asi jako celé Chorvatsko nebo 25% České republiky
– Temelín na plný výkon
12 OpenLab: Cryptocurrencies
https://digiconomist.net/bitcoin-energy-consumption
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Všechny bloky jsou veřejné (blockchain)
• Jednotlivé bloky s transakcemi jsou provázané
• Tvoří veřejnou historii všech provedených transakci
• Každý si může zkontrolovat platnost transakce– Snadné, stačí ověřit hash na bloku a podpis na transakci
13 OpenLab: Cryptocurrencies
Blockchain
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Jak si udělat digitální peněženku?
• Papírová
• Aplikace na mobilním telefonu– Coinomi, JAXX
• Čipová karta (Ledger nano)
• Burzy (použití při obchodování)
• Jak získat digitální peníze?– Nákup bitcoinů v bankomatu (Omega, Vaňkovka)
• Následně směna za libovolnou kryptoměnu
– Převodem Kč na burzu, nákup vybrané kryptoměny14 OpenLab: Cryptocurrencies
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Má to cenu?
15 OpenLab: Cryptocurrencies
1฿ = 270Kč
1฿ = 20tis Kč
1฿ = 5tis Kč
1฿ = 100tis Kč
Bitcoiny za 1000 Kč v roce 2010 mají dnes hodnotu přes 800tis Kč
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Other cryptocurrencies (altcoins)
• Why something else than Bitcoin?
1. Cost of transaction– >$2 at the moment (for every transfer)
2. Time to confirm transaction (+ limited block size)– 4 blocks inside chain commonly required, ~10 minutes per block
3. Traceability (anonymity) of transactions– Source, destination and amount is public
4. Centralization of computation– China mining rigs with ASICs
5. Limited scripting language– For more complicated smart contracts
16 OpenLab: Cryptocurrencies
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• Copycats – Take Bitcoin’s source code and change the name and icon
– E.g., Litecoin (but LTC is now adding new features before Bitcoin)
• Bitcoin-style, but adding some distinct features – Ethereum: Turing-complete scripting for smart contracts, proof-of-ownership
– Zcash: zero-knowledge proof for sender/receiver/amount (shielded transactions), ASIC-resistant proof of work (large memory required)
– Monero: private transactions via mixing
• More traditional styles (Ripple, NEM), focused on banks – decentralized network of verification nodes (faster and cheaper txs)
– but less privacy and overall resilience against central control
• Initial Coin Offerings (ICO)– Basically crowdfunding campaign (often via Ethereum smart contracts)
– Frequently scam, recently banned by China
Other cryptocurrencies (altcoins)
17 OpenLab: Cryptocurrencies
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More than 700 altcoins now!
18 OpenLab: Cryptocurrencies
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Crypto trading
19 OpenLab: Cryptocurrencies
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Hands on - SysCoin
• Why Syscoin?– Probably a “shit” coin (but good for experiments)
– Cheap coin ($0.15/SYS), very low transaction fee
– New block every minute (so we don’t need wait long)
– Principles same as for the more expensive currencies
• Generate own wallet– Paper wallet: https://WalletGenerator.net
• Ideally download from GitHub, run offline via LiveCD…
– Mobile wallet (Coinomi Android)
• Generate new public key (Receive)
20 OpenLab: Cryptocurrencies
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21 OpenLab: Cryptocurrencies
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Hands on – SysCoin II.
1. I will send some SYS to your wallet
2. Resend some fraction to your friend(s)
3. Observe your transaction(s) at https://chainz.cryptoid.info/sys/
– Can you find your transaction?
– Can you figure out Dusan’s initial amount of SYS?
– Can you figure out my initial amount of SYS?
– Can you figure out how I obtained my SYS?
– Can you track other’s transactions?
– Can you decide if output transaction was already spend?
22 OpenLab: Cryptocurrencies
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What next?
1. Just enjoy the knowledge ☺
2. Possibly buy some (small) amount of Bitcoins (ATM) and investigate the options
3. Play with some virtual portfolio – e.g., https://www.worldcoinindex.com/portfolio
– Create virtual set of favourite coins and observe gain/loss
4. Possibly register on some exchange– Kraken, Coinbase…
23 OpenLab: Cryptocurrencies