Blockchains and co, with only 2 hours

Technical conference given to students of ENSSAT (enssat.fr) to introduce to them the universe of blockchains (in 2 hours).

Talk about history of cypherpunks, blockchains, cryptocurrencies, tokens, decentralized applications, use cases and laws.

Slidedeck under CC-BY.

You enjoyed reading these slides? Buy me a beer, thanks<3
(https://pylapersonne.info/buymeacoffee)

Transcript

1. Blockchains & co
   with only ~120’
   Release 4 - 11/23/2018 ✿✿✿✿ ʕ •ᴥ•ʔ/ ︻デ═一 Cette œuvre est mise à disposition selon les termes de la Licence Creative Commons Attribution 4.0 International.
   

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2. Pierre-Yves Lapersonne
   software developer
   pylapersonne.info
   

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3. several parts
   1. History
   2. Blockchains
   3. Cryptocurrencies
   4. ÐApps
   5. Use cases
   6. Laws
   

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4. history
   

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5. crypto-anarchism, cypherpunk and mathematics...
   ● 1992: cypherpunks
   ○ Timothy May
   ○ The Cypherpunks Mailing List
   ○ release of The Cyphernomicon (1994)
   ○ missions including protection of privacy using encryption
   ○ crypto-anarchism
   ● 1998: b-money
   ○ Wei Dai
   ○ b-money, an anonymous, distributed electronic cash system
   ○ base of future blockchains: proof of work, transactions, broadcast
   ● 2005: bit gold
   ○ Nick Szabo
   ○ Bit Gold: Towards Trust-Independent Digital Money
   5
   

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6. and shit happened.
   ● 2008: subprimes crisis !
   ○ too much speculation
   ○ massive loss of money for people
   ○ some banks were definitely closed
   ○ some banks were nationalized
   ○ loss of confidence to usual financial systems
   ● 2008: Bitcoin
   ○ Satoshi Nakamoto
   ○ Bitcoin: A Peer to Peer Electronic Cash System
   ○ birth of the 1st cryptocurrency!
   6
   

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7. the first block
   ● 3 January 2009
   ○ 1st mined block - block genesis
   ○ 1st blockchain started
   ○ 1st transaction including a troll
   7
   

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8. the first blockchain
   ● new paradigm, new hopes
   ○ decentralized architecture
   ○ without regulation
   ○ unfalsifiable content
   ○ not anonymous
   ○ holds only bitcoin transactions
   ○ based on a fair consensus: mathematical challenge
   ○ dedicated to micro-transactions
   8
   bitcoin BTC 1
   milli-bitcoin mBTC 0.001
   micro-bitcoin μBTC 0.000001
   satoshi sat 0.00000001
   millisatoshi msat 0.00000000001
   

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9. blockchains
   

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10. 1a - transaction
    ● sender
    ● receiver
    ● balance of tokens
    ● payload (depending to the
    blockchain in use)
    10
    

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11. inside a transaction (Bitcoin)
    11
    sender address
    139emjfbkBGkE..............KMRS
    blockchain.info
    receiver address
    19ZVvhHpnd3Tc..........NNCAmn
    

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12. inside a transaction (Ethereum)
    12
    smart contract
    code of smart contract
    etherscan.io
    

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13. 1b - transactions
    ● triggered once registered
    in the blockchain
    ● each transaction has a cost
    (Tx fees)
    ● transactions are stored
    inside a pool before being
    added
    ● Tx fees order the
    transactions
    13
    Number of BTC transactions in pool (10/30/2018)
    bitcointicker.co
    

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14. 2 - block
    ● gathers several
    transactions
    ● contains useful details for
    the blockchain, e.g. :
    ○ timestamp
    ○ transaction fees
    ○ relay
    ○ difficulty, nonce
    ○ hashtree root
    ○ ...
    ● must be added only 1 time
    14
    

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15. 15
    inside a block
    mining pool
    hash of block #493761
    root of the hash tree
    blockchain.info
    

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16. 3a - consensus
    ● miners may solve a hard
    mathematical problem to
    choose the one who will
    add the block and trigger
    the transactions stored
    inside
    ● challenge = consensus
    ○ Proof Of Work
    ○ Proof of Stake
    ○ Proof of Authority
    ○ Proof of Importance
    ○ ...
    16
    ? ?
    ?
    ?
    ?
    

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17. 3b - proof of work
    1. build of a local block with
    ○ hash of previous block
    ○ hashtree root for tx
    ○ difficulty
    ○ ...
    1. find the golden nonce, i.e. the
    random value with makes the
    block hash lower than the
    difficulty
    ➔ brute force!
    17
    Blockchain Bitcoin Ethereum Monero Dogecoin
    Difficulty 7 184 404
    942 702
    2 986 685
    821 724 284
    61 820 335
    411
    2 716 801
    Block time 10’50’’ 14.3’’ 2’2’’ 1’2’’
    ● 11/07/2018
    ● bitinfocharts.com
    hash n-1
    hash
    algorithm hash n
    nonce
    

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18. 3c - block mining
    ● with CPU or GPU
    ● with FPGA or ASIC
    ● with mining pools
    18
    Distribution of hashrates in Bitcoin blockchain (11/09/2018)
    blockchain.info/pools
    

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19. 3d - rewards
    ● blockchains are alive thanks to
    their transactions
    ● transactions use tokens
    ● tokens should be released
    regularly
    ➔ how can we make the system
    dynamic and attractive?
    Miners earn transaction fees and
    rewards
    19
    Blockchain Reward USD
    Bitcoin 12.5 BTC $ 81 846.75
    Bitcoin Cash 12.5 BCH $ 7 865.63
    Bitcoin Gold 12.5 BTG $ 392.38
    Litecoin 25 LTC $ 1 373.5
    ZCash 12.5 ZEC $ 1 626
    Ethereum 3 ETH $ 660.24
    Ethereum Classic 4 ETC $ 38.96
    Monero 3.6 XMR $ 400.176
    ● 11/07/2018
    ● bitinfocharts.com
    

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20. 4a - blockchain
    20
    ● each block has a
    fingerprint of the previous
    block (hash)
    ● each block
    has a
    fingerprint of
    the previous
    block (hash)
    hash n-1 hash n
    hash n-2
    bloc n - 1 bloc n bloc n + 1
    hash hash
    

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21. 4b - blockchain
    ● each block
    has a
    fingerprint of
    the previous
    block (hash)
    21
    hash n-1 hash n
    hash n-2
    bloc n - 1 bloc n bloc n + 1
    hash hash
    ● each block has a
    fingerprint of the previous
    block (hash)
    ● to corrupt a block, we must
    modify all the following
    blocks
    ● a strong protocol is applied
    to check the blockchain
    and ensure its integrity
    hash of corrupted block
    

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22. 5 - network
    ● the blockchain is replicated
    in each node of the
    network
    ● if we want to corrupt a
    blockchain, we have to
    corrupt all blockchains
    before the next update
    ● this kind of attack implies
    too much energy and
    computational power
    22
    full node
    lite node
    

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23. cryptocurrencies
    

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24. 2090
    ?
    24
    

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25. 2090
    cryptocurrencies in use at least
    (899 coins + 1191 tokens)
    ● 11/07/2018
    ● coinmarketcap.com
    25
    

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26. tokens or not tokens...
    “Simple” cryptocurrencies
    ● more for “1st generation blockchains”
    Tokens
    ● related to “2nd generation blockchains”
    ● implement ERC20 or ERC721 standards
    ● used with smart contracts
    26
    

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27. ERC {20 | 721}
    ERC 20
    ● fungible
    ● ~ implemented by a lot of
    cryptocurrencies
    ● looks like fiat currencies
    ● can be sliced into smaller fragments
    ERC 721
    ● not fungible (= unique)
    ● cannot be sliced
    ● “manufactured collectible”
    27
    

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28. types of tokens
    payment tokens
    ● dedicated blockchains
    ● inherent value
    ● for financial transactions
    ● real cryptocurrencies
    security/equity tokens
    ● represent assets
    ● can be seen like securities,
    derivatives, ...
    ● used in ICO
    28
    utility tokens
    ● provided access to services
    ● dedicated for use cases
    

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29. bubbling world
    29
    ETH vs ETC
    ● June 17, 2016
    ● hack of TheDAO
    ● ~ 3 600 000 stolen ETH (~ 70 000 000 USD at the time)
    ● → hard fork to cancel the theft (Ethereum)
    ● a part of the community refused
    ● = birth of Ethereum Classic (no fork)
    

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30. bubbling world
    30
    BTC vs BTG vs BCH...
    ● upgrade of BTC blockchains with SegWit to increase speed of transactions and blocks sizes
    ● → contentions in community
    ● = hardfork (07/2017) giving birth to Bitcoin Cash
    ● need to mine bitcoins without ASIC
    ● = hardfork (10/2017) giving birth to Bitcoin Gold
    

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31. really bubbling world
    31
    (ﾉಥ益ಥ）ﾉ ... vs BCHABC vs BCHSV
    ● November 2018
    ● a civil war between two camps...
    ● conflict between rich people about vision, control, influence (and also block sizes)
    ● Craig Wright vs Roger Ver (and the rest of the world)
    ● hashwar to get rid of the opponents
    ● = hardfork splitting Bitcoin Cash to Bitcoin ABC and Bitcoin SV
    

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32. not a fork story... but a spaghetti story (－‸ლ)
    

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33. Bitcoin
    ● January 3, 2009
    ● limited quantity to 21 millions
    of BTC
    ● 1 BTC = 6 544.28 USD
    ● 10’5’’ blocktime
    ● 12.50 BTC + Tx Fees rewarded
    ● hashrate of 47.46 Ehash/s
    ● proof of work (Hashcash)
    Grandpa cryptocurrency
    33
    BitInfoCharts (11/07/2018)
    

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34. Bitcoin
    ● no privacy
    ● not anonymous
    ● too few minable without mining
    pool
    ● massive speculation
    ● very bubbling
    ● network consumption ~ 1% of
    world energy consumption
    Grandpa cryptocurrency
    34
    

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35. Monero
    ● April 18, 2014
    ● unlimited quantity of XMR
    ● 1 XMR = 111.6 USD
    ● 2’2’’ blocktime
    ● 3.63 XMR + Tx Fees rewarded
    ● hashrate of 502 Mhash/s
    ● proof of work (CryptoNight)
    “secure, private, untraceable”
    (today)
    35
    BitInfoCharts (11/07/2018)
    

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36. Monero
    ● sender address is protected
    (Ring Signatures)
    ● receiver address is protected
    (Stealth Addresses)
    ● transaction balance is
    protected (Ring Confidential
    Transactions)
    ● broadcast of transactions is
    protected (Kovri)
    ● XMR balances not related to
    public addresses
    “secure, private, untraceable”
    (today)
    36
    

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37. ZCash
    ● October 28, 2016
    ● limited quantity to 21 millions
    of ZEC
    ● 1 ZEC = 130.88 USD
    ● 2’32’’ blocktime
    ● 12.50 ZEC + Tx Fees rewarded
    ● hashrate of 2.27 Ghash/s
    ● proof of work (Equihash)
    Snowden approved
    37
    BitInfoCharts (11/07/2018)
    

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38. ZCash
    ● sender and receiver addresses
    are shielded (z-addr) or not
    (t-addr)
    ● z-addr are protected with a Non
    Interactive Zero Knowledge
    Proof method (zk-SNARK)
    ● public blockchain but private
    project driven by the Zerocoin
    Electric Coin Company
    Snowden approved
    38
    

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39. Ether
    ● July 30, 2015
    ● unlimited quantity of ETH
    ● 1 ETH = 220.11 USD
    ● 14.3’’ blocktime
    ● 3 ETH + Tx Fees rewarded
    ● hashrate of 238 Thash/s
    ● proof of work (Ethash)
    Ethereum powered
    39
    BitInfoCharts (11/07/2018)
    

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40. Ether
    Ethereum powered
    40
    ● token for the 1st blockchain of
    2nd generation
    ● cryptocurrency in use for smart
    contracts
    

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41. Basic Attention
    Token
    Be brave
    41
    ● May 31, 2017
    ● hosted on Ethereum
    ● 1 BAT = 0.33 USD
    ● created by Brendan Eich
    ● integrated to Brave browser
    ● designed to value and price
    humain attention (for fair ads)
    ● 30’’ to raise 35 millions USD
    during the ICO
    

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42. 42
    ● ICO from 12/01/2017 to
    01/01/2018
    ● hosted on Ethereum
    ● 1 CO2 = 3.81 USD
    ● trade the carbon using tokens
    ● try to build a “blockchain green
    ecosystem” (not a joke)
    Climatecoin
    Save the planet, trade the
    carbon
    

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43. Ðecentralized apps
    

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44. the 2nd generation of blockchains
    ● 2013: Ethereum
    ○ Vitalik Buterin
    ○ was only 19 y.o.!
    ● blockchains are:
    ○ decentralized
    ○ replicated (distributed)
    ○ not regulated
    ○ use tokens
    ○ have blocks with financial transactions
    ● and what if we put programs in blockchains?
    ○ Ðecentralized applications
    The Ethereum Experience
    44
    

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45. programs in blockchain!
    45
    ● use of virtual machine
    ○ Ethereum Virtual Machine (EVM)
    ● transactions have bytecode in payload
    ● execution of programs are conditioned
    ○ tokens are used to process instructions
    ■ ETH, ETC, ...
    ○ each instruction has a cost
    ■ gas
    ● nodes of network check outputs of programs
    ● Ethereum can be seen as kind of “slow” database/register
    ● Ethereum Yellow Paper
    ● Gas Costs from Yellow Paper
    

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46. a gas story
    46
    ● gas is used so as to evaluate:
    ○ costs of instructions
    ○ fees of transactions (TxFees)
    ○ value of transactions earned by miners
    final cost of the transaction, earned by miner
    wei = unit for gas
    the amount of gas to burn to process the program of the smart contract,
    which depends to the amount of code to process
    ● the lower the price is, the less gainful the transaction is,
    the later the transaction will be mined
    ● allow to involve the cost of the transaction
    

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47. TxFees in Ether based on gas
    47
    Ether = Tx Fees = Gas Limit * Gas Price
    ETH Gas Station
    

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48. a new paradigm
    48
    ● “Old” paradigms
    ○ sequential ➞ 1 computer processing series of N instructions
    ○ parallel ➞ 1 computer processing K (in N) instructions at the same time (threads)
    ○ distributed ➞ X computers processing samples of the N instructions
    ● Decentralized paradigms
    ● X computers processing at the same time the N instructions
    ● programs are duplicated in computers
    ● no more unique server or backend which hosts the program
    →no authorities to trust
    →no centralisation to fail
    →but slower than centralized solutions
    

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49. layers of Ðapps
    49
    The Ethereum Experience
    

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50. architecture of web Ðapps
    Ethereum
    blockchain
    (dev)
    Ethereum
    network
    (prod)
    web server
    smart contract
    sources
    (.sol)
    smart contract
    ABI
    (.js, .json)
    web app
    (.html, .css, .js, ...)
    hosting
    compilation
    inclusion
    deployment
    web browser
    

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51. logic with smart contracts
    49
    ● have balance of tokens and unique address
    ● the code is law
    ● hosted in the blockchain
    ● once deployed, cannot be
    ○ removed
    ○ modified
    ● if bugs or flaws appear
    ○ write a new contract!
    51
    More about smart contracts
    ÐApps on Ethereum with Solidity
    

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52. need to optimize Ðapps on blockchains
    52
    ● Ðapps must be optimized
    ○ choose the best functions
    ○ be aware with storage of data
    ○ use the most suitable data types
    ○ decrease complexity of functions
    ● If the program is:
    ○ dirty
    ○ heavy
    ○ not enough well written
    ➔ may burn a lot of gas
    ➔ must be expensive in Ether
    

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53. use cases
    

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54. which use cases?
    54
    ● payment
    ○ e.g. Keplerk
    ● products tracking
    ○ e.g. IBM Food Trust
    ○ e.g. Connecting Food
    ● fight against censorship, fake news...
    ○ e.g. PUBLIQ
    ● citizenship
    ○ e.g. online vote using blockchains
    ● insurance
    ○ e.g Etherisc
    ● documents and securities transfer, ...
    

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55. laws
    

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56. governments and states may be scared
    56
    ● forbidden
    ○ e.g Algeria, Bolivia, China, Ecuador, Egypt, Iran, Morocco
    ● more or less regulated
    ○ e.g Canada, France, Singapore, USA
    ● supported
    ○ e.g Estonia, Japan
    ● used for national cryptocurrencies
    ○ e.g Estonia (Estcoin?), Venezuela (Petro)
    

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57. conclusion
    

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58. blockchains & cryptocurrencies
    58
    ● are not yet mature enough
    ● may be censored, controlled or regulated by governments
    ● are occulted by the hype around Bitcoin (-_-)”
    ● enhance and boost innovations and technical challenges
    (ﾉ^_^)ﾉ we can think using a new framework:
    decentralization
    

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59. thanks!
    

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60. links (⌐□_□)
    

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61. Tools
    ● BitInfoCharts
    ● Coinbase
    ● ETH Gas station
    ● Ethereum Natural Specification Format
    ● Ethereum Network Status
    ● Ethernodes
    ● Etherscan
    ● Etherscan ByteCode to Opcode Disassembler
    ● Etherscan gas price
    ● Ganache
    ● Geth
    ● Infura
    ● Loom
    

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62. Tools
    ● Metamask
    ● Mist
    ● Monero Blockchain Explorer
    ● Open Zeppelin
    ● Porosity
    ● Remix IDE
    ● State of the ÐApps
    ● Truffle
    ● Web3
    ● Zchain
    

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63. References
    ● 9 Types of Consensus Mechanisms That You Didn’t Know bout, Daly Bit
    ● A 101 Noob Intro to Programming Smart Contracts on Ethereum, ConsenSys
    ● Basic Attention Token, basicattentiontoken.org
    ● Basic Attention Token (BAT), Brave Software
    ● Bitcoin: A Peer-to-Peer Electronic Cash System, Satoshi Nakamoto
    ● Bitcoin: The Cryptoanarchists’ Answer to Cash, Morgen E. Peck
    ● Bitcoin Cash’s ‘Mining War’ Escalates as Blockchain Hard Fork Approaches, Nikhilesh De
    ● Bitcoin Is Terrible for the Environment, Emily Atkin
    ● Bit Gold and Bitcoin, In Search Of Satoshi
    ● Bloc Genesis, bitcoin.fr
    ● Blockchain Security Mechanisms, Shaan Ray
    ● Climatecoin, climatecoin.io
    ● Create Your Own Crypto-currency with Ethereum, ethereum.org
    ● Crossing Over to Web3 - An Introduction to Decentralised Development, Luke Hedger
    ● CryptoKitties, cryptokitties.co
    ● Cryptomonnaies - mode d’emploi en 20’, Pierre-Yves Lapersonne
    ● ÐApps on Ethereum with Solidity, Pierre-Yves Lapersonne
    ● Decentraland, decentraland.org
    ● Demystifying Hashgraph: Benefits and Challenges, Yaoqi Jia
    ● Ethash, github.com/ethereum
    Web sites visited on 11/23/2018
    

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64. References
    ● Ethereum ERC 721 vs ERC 20, Patrick Goh
    ● Ethereum: Ether, Ether Gas, Gas Limit, Gas Price & Fees [...], Sudhir Khatwani
    ● Ethereum “Gas” - How it works, steemit.com
    ● Everything You Need to Know About [...] Sapling Upgrade [...], John Westbrook
    ● Full-stack smart contract development, Júlio Santos
    ● Hashgraph wants to give you the benefits of blockchain without the limitations, Samantha Stein
    ● Hedera Hashgraph, hederahashgraph.com
    ● How to build your own Ethereum based ERC20 Token and launch an ICO in next 20 minutes, Sandeep Panda
    ● Hyperledger, hyperledger.org
    ● Introduction to Smart Contracts, solidity.readthedocs.io
    ● Kovri, getkovri.rg
    ● La Révolution des Blockchains, Pierre-Yves Lapersonne
    ● Ledger Legends, ledgerlegends.com
    ● Les bitcoins dans les bureaux de tabac, une information fumeuse, Maxime Vaudano & Pierre Breteau
    ● Les cryptomonnaies sont-elle halal ?, Gregory Raymond
    ● Multisignature, en.bitcoin.it
    ● Proof of Work vs Proof of Stake: Basic Mining Guide, blockgeeks.com
    ● Reversing EVM bytecode with radare2, Fedor Sakharov
    ● Ring Confidential Transactions, Shen noether, Adam Mackenzie and Monero Core Team
    ● Ring signature, wikipedia.org
    Web sites visited on 11/23/2018
    

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65. References
    ● Stealth Address and Key Management Techniques in Blockchain Systems, N. Courtois, R. Mercer
    ● Swarm, swarm-guide.readthedocs.io
    ● The Cyphernomicon, nakamotoinstitute.org
    ● The Ethereum Experience, Ethereum
    ● The Next Generation of Distributed Ledger Technology, iota.org
    ● The Story of the DAO - Its History and Consequences, Samuel Falkon
    ● The Tangle, Serguei Popov
    ● The Tangle: an Illustrated Introduction, Alon Gal
    ● Types of Consensus Protocols Used in Blockchains, Evan Tan
    ● Types of tokens. The four mistakes beginner crypto-investors make, ICOscoring
    ● Understanding Blockchain Fundamentals, Part 1: Byzantine Fault Tolerance, Georgios Konstantopoulos
    ● Understanding Segregated Witness, Jimmy Song
    ● Vie privée, telle est ma devise, Pierre-Yves Lapersonne
    ● W-ETH, weth.io
    ● Walking Through the ERC721 Full Implementation, Karen Scarbrough
    ● WBTC, www.wbtc.network
    ● What are Sidechains?, Shaan Ray
    ● When I say mine you say Coinhive, Pierre-Yves Lapersonne
    ● Whisper, github.com/ethereum
    Web sites visited on 11/23/2018
    

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66. Credits
    ● Logo of AudioCoin - ?, modified with GIMP
    ● Logo of Augur - AugurProject, CC BY-SA International 4.0, modified with GIMP
    ● Logo of Basic Attention Token - Bradley Richter, CC BY-SA International 4.0, modified with GIMP
    ● Logo of Brave - Copyright © Brave Software Inc.. All Rights Reserved, modified with GIMP
    ● Logo of Bitcoin - Bitboy, public domain, modified with GIMP
    ● Logo of Bitcoin ABC - ?, modified with GIMP
    ● Logo of Bitcoin Cash - Amaury Sechet, CC0 1.0 Universal Public Domain Dedication, modified with GIMP
    ● Logo of Bitcoin Gold - Bitcoin Gold, public domain, modified with GIMP
    ● Logo of Bitcoin SV - ?, modified with GIMP
    ● Logo of climatecoin - ?, modified with GIMP
    ● Logo of Code d’Armor - Copyright © Code d'Armor. All Rights Reserved.
    ● Logo of CSS3 - icones8.fr
    ● Logo of Dash - dash.org, CC BY-SA International 4.0
    ● Logo of Dogecoin - Copyright © The Ðogecoin Project. All Rights Reserved, modified with GIMP
    ● Logo of ENSSAT - Copyright © ENSSAT. All Rights Reserved.
    ● Logo of eosio - eosio, block.one, public domain, modified wih GIMP
    ● Logo of Ethereum - Ethereum Foundation, CC BY Unported 3.0, modified with GIMP
    ● Logo of Ethereum Classic - Ethereum Classic, CC0 1.0 Universal Public Domain Dedication, modified with GIMP
    ● Logo of Filecoin - Copyright © Protocol Labs. All Rights Reserved, modified with GIMP
    ● Logo of Ganache - Copyright © Consensys. All Rights Reserved, modified with GIMP
    ● Logo of Gnosis - Copyright © Gnosis Ltd. All Rights Reserved, modified with GIMP
    ● Logo of Golem - Copyright © Golem Factory GmbH. All Rights Reserved, modified with GIMP
    ● Logo of HTML5 - Copyright © W3C, CC BY 3.0
    ● Logo of IOTA - Copyright © IOTA Foundation. All Rights Reserved, modified with GIMP
    ● Logo of Kairos - Copyright © Kairos AR, Inc. All Rights Reserved.
    ● Logo of JavaScript - javatpoint.com, modified with Gimp
    ● Logo of Litecoin - Losh1212, CC BY-SA International 4.0, modified with GIMP
    ● Logo of MetaMask - metamask.io, modified with GIMP
    ● Logo of Monero - The Monero Project, CC BY 3.0, modified with GIMP
    ● Logo of Ripple - Ripple, public domain, modified with GIMP
    ● Logo of Solidity - Copyright © Ethereum Foundation, CC BY-SA 3.0, modified with GIMP
    ● Logo of Truffle - Copyright © Consensys. All Rights Reserved, modified with GIMP
    ● Logo of ZCash - Copyright © ZCash. All Rights Reserved, modified with GIMP
    ● Pictures - Freepik, Flaticon Basic License
    ● Bitcoin free icon - Pixel Buddha, Flaticon Basic License
    ● Exploding free icon - OCHA, CC 3.0 BY
    ● Invisible person of clothes free icon - Freepik, Flaticon Basic License
    ● Troll Face Png Available In Different Size - freeiconspng.com
    ● Runner silhouette running fast free icon - Freepik, Flaticon Basic License
    

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