A fast paced review of blockchain technology, applications, architectural characteristics and programming, using Ethereum as the main example. Presented at the JAX London 2017 conference.

1. A Breathless Tour
of Blockchain
Eoin Woods
Endava
@eoinwoodz
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licensed under a Creative Commons Attribution-ShareAlike 4.0 International License

2. Agenda
• What is Blockchain?
• Applications for Blockchain
• Blockchain as an Architectural Element
• Programming the Blockchain
• Summary
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3. What is Blockchain?
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4. What is Blockchain?
• The enabling technology of Bitcoin
• A distributed database without a controlling authority
• An auditable database with provable lineage
• A way to collaborate with principals without trust
• Trust and storage mechanism for cryptocurrencies
• Architectural component for Internet-scale systems?
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5. What is Blockchain? Basic terms
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Crypto Currencies Ether
Distributed Ledger P2P distributed,
append-only, transaction list
Blockchain cryptographic validation,
distributed consensus mechanism
Smart Contracts code embedded in the blockchain,
manipulates the blockchain state

6. What is Blockchain? Bitcoin network example
Miners
Bob Alice
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7. What is Blockchain? Blockchain structure
Transaction 1
Transaction 2
Transaction 3
Block Hash
Prev Block Hash
Transaction 4
Transaction 5
Transaction 6
Block Hash
Prev Block Hash
Transaction 7
Transaction 8
Transaction 9
Block Hash
Prev Block Hash
Transaction 10
• Public keys identify participants
• Bitcoin addresses identify participants in a transaction (derived from PK)
• Cryptographic hashes used to ensure integrity 7

8. What is Blockchain? Consensus
Q. How do we know the information on the chain is correct?
A. Because everyone agrees – this is “consensus”
Blockchains use different types but “proof of work” is common
• To create (“mine”) a block you need to solve a hard problem
• If you don’t solve the problem then peers will reject your block
• Thus forging the blockchain would require a huge amount of work to get
your fraudulent blocks accepted (“impossible” without 51% of capacity)
Other models including “proof of stake” and “proof of membership”
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9. Applications for Blockchain
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10. What blockchains exist?
A lot of blockchain implementations exist. A small sample of them are:
Bitcoin 2009 Cryptocurrency
Litecoin 2011 Cryptocurrency
Ripple 2012 Blockchain payment and settlement system
Chain 2014 Enterprise blockchain
Ethereum 2015 Blockchain dapp platform
Hyperledger 2015 Linux Foundation open source blockchain projects
R3 Corda 2016 Distributed ledger for the financial industry
Multichain 2017 Enterprise blockchain
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11. Cryptocurrencies – August 2017
10 cryptocurrencies
market cap of > $1B
Bitcoin is $70B.
source: coinmarketcap.com
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12. Cryptocurrencies – September 2017
11 cryptocurrencies
market cap of > $1B
Bitcoin is $62B.
source: coinmarketcap.com
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13. Sidenote: Cryptocurrency Volatility
13source: coinmarketcap.com

14. What is Blockchain being Used For?
Trade Settlement
and FX Transactions
digital ledger that tracks and
protects valuable assets
verifiable supply chains
post-trade processing
Keybase
Identity management verified data
Georgia government
records
supply chain efficiency
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15. Properties of a Good Blockchain Application
• Multiple separate parties want to cooperate
• No central intermediary exists (or is wanted)
• Relatively slow moving processes (allow latency)
• Well-defined, bounded process
• Predictable, simple data access required
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16. Demo: Browse a blockchain
blockchain.info
Most public blockchains have a range of associated web based “explorers”
• For Bitcoin we’ll use blockchain.info
• For Ethereum we’ll use etherscan.io
etherscan.io 16

17. Demo: Explore a blockchain
• The WannaCry ransomware attackers have 3 bitcoin wallets:
• 13AM4VW2dhxYgXeQepoHkHSQuy6NgaEb94
• 115p7UMMngoj1pMvkpHijcRdfJNXj6LrLn
• 12t9YDPgwueZ9NyMgw519p7AA8isjr6SMw
• We can use blockchain.info to find out how much they have
collected in ransom so far and where they sent it
• Note: if using the API it returns values in satoshis: there are 10-8 satoshis in a
bitcoin, so multiply by 0.00000001 to get BTC
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18. Blockchain as an
Architectural Element
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19. Characteristics of a Blockchain Ledger
• Distributed, replicated “database”
• Distribution via a p2p model (no master)
• Consensus model used to ensure integrity
• Append only “immutable” store
• Highly fault tolerant
• Eventually consistent
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20. Adding Smart Contracts
• Code stored in a blockchain, executed by the
blockchain virtual machine
• Programming models vary by platform
• Bitcoin - primitive ”Forth” script
• IBM Hyperledger – GoLang
• Ethereum - Solidity
• Ethereum Solidity is our example in this session
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21. Example: Ethereum Solidity Smart Contract
contract Coin {
// The keyword "public" makes those variables readable from outside.
address public minter;
mapping (address => uint) public balances;
// Events allow light clients to react on changes efficiently.
event Sent(address from, address to, uint amount);
// This is the constructor whose code is run only when the contract is created.
function Coin() { minter = msg.sender; }
function mint(address receiver, uint amount) {
if (msg.sender != minter) return;
balances[receiver] += amount;
}
function send(address receiver, uint amount) {
if (balances[msg.sender] < amount) return;
balances[msg.sender] -= amount;
balances[receiver] += amount;
Sent(msg.sender, receiver, amount);
}
} 21
// More details later …

22. Quality Properties of a Distributed Ledger
Useful Qualities
• Append only
• Security (integrity, non-
repudiation, availability)
• High fault-tolerance
• No single point control or trust
• Embedded immutable logic
• Dynamic, evolving ecosystem
Problematic Qualities
• (very) eventual consistency
• computationally expensive
(generally)
• Limited query model
• Lack of privacy
• lack of throughput scalability
(generally – 10s txn/sec)
• Lacking maturity
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23. Aside: Storing Data
• Blockchains not designed for
large data items
• Some (Bitcoin) optimised for
many small transactions
• Large data stored “off chain”
• e.g. IPFS and Swarm
• Store pointer in blockchain
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24. Integrating Blockchain
Blockchain
Application
(Dapp)
Conventional
Application
Blockchain (e.g. Ethereum) Immutable Storage
(e.g. Swarm, IPFS)
object references
queries, transactions,
smart contract invocations
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25. Thinking Point: Applying Blockchain
• What could you use blockchain for?
• At work or to change the world!
• What problems would it solve or introduce?
Recap
• distributed, highly reliable, auditable, immutable database,
not requiring trust between participants
• smart contracts can embed computation in it
• but slow, eventually consistent, limited queries
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26. Programming Blockchain
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27. Smart Contracts
• The “programming” bit of blockchain technology
• Code in the blockchain executed by the runtime
• Any participant can add a smart contract (for a fee)
• Contract usually mutates the state of the blockchain
• add another transaction
• Transforms blockchain to a dynamic system
• A bit like triggers and stored procedures in RDBMS
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28. Bitcoin “Script”
• Very simple “FORTH-like” virtual machine
• Constrained programming model of “locking” and ”unlocking” scripts
• Locking script (“scriptPubKey”) defines constraints to execute the transaction
• Unlocking script (“scriptSig”) satisfies the constraints to allow execution
• Small number of “op codes” for use in scripts.
Example
Lock: OP_DUP OP_HASH160 <payee pub key hash> OP_EQUAL OP_CHECKSIG
Unlock: <payee signature> <payee pub key>
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29. Bitcoin “Script”
<payee signature> <payee pub key>
OP_DUP OP_HASH160 <payee pub key hash> OP_EQUAL OP_CHECKSIG
Stack based execution:
<payee pub key>
<payee signature>
<payee pub key>
<payee pub key>
<payee signature>
<payee pub key hash>
<payee pub key>
<payee signature>
<payee pub key hash>
<payee pub key hash>
<payee pub key>
<payee signature>
<payee pub key>
<payee signature>
(Push 2 arguments) OP_DUP OP_HASH160 (Push argument)
OP_EQUAL (= T)
OP_CHECKSIG (= T)
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30. Ethereum Solidity
• Most popular contract language for Ethereum
• Turing complete, object-oriented language
• Inheritance and user-defined types
• Compiles to bytecode that runs on the EVM
• Emerging eco-system of frameworks and tools
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31. Ethereum Solidity
contract Coin {
// The keyword "public" makes those variables readable from outside.
address public minter;
mapping (address => uint) public balances;
// Events allow light clients to react on changes efficiently.
event Sent(address from, address to, uint amount);
// This is the constructor whose code is run only when the contract is created.
function Coin() { minter = msg.sender; }
function mint(address receiver, uint amount) {
if (msg.sender != minter) return;
balances[receiver] += amount;
}
function send(address receiver, uint amount) {
if (balances[msg.sender] < amount) return;
balances[msg.sender] -= amount;
balances[receiver] += amount;
Sent(msg.sender, receiver, amount);
}
}
Contract
Typed state
Event for log
(and callback)
Functions to
operate on
state
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32. Solidity & Ethereum Development Ecosystem
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Geth Eth Pyethapp Clients for JS, .NET and Java
Development Tools
Mist Wallet MetaMaskether.camp

33. Summary
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34. Key Concepts
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Distributed Ledgers
• p2p append-only transaction stores
Blockchains
• cryptographically validated ledgers
Smart Contracts
• immutable code changing blockchain state

35. What is Blockchain?
• A novel type of distributed transaction store
• Append-only, auditable, fault tolerant, secure by design
• Can be slow and high-latency by accident
• Most host “smart contract” code to provide secure
computations
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36. Some Applications
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Value Transfers: securities clearing, payments
Verifiable Records: property registers, supply chain,
loyalty points
Identity: verifiable digital identity, passports
Verifiable Storage: immutable storage of digital assets
Decentralised Notary: proof of existence of digital asset
Currencies: Bitcoin, Ether, Litecoin, …

37. To Find Out more
• Bitcoin – bitcoin.org
• Ethereum – ethereum.org
• Solidity - solidity.readthedocs.io
• Truffle - truffleframework.com
• Embark - github.com/iurimatias/embark-framework
• Dapp - dapp.readthedocs.io
• IPFS – ipfs.io
• Swarm - swarm-gateways.net
• News – coindesk.com, cryptoinsider.com (and many others)
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38. Eoin Woods
Endava
eoin.woods@endava.com
@eoinwoodz
Thank You
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