is blockchain the savior of the media industry? · •blockchain does not need to have distributed...
TRANSCRIPT
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Is Blockchainthe Savior of the Media Industry?
ERIC DIEHL
VP, Security and Media Technologies
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REALLY?
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•Blockchain 101•Mythology•Consensus?•Smart contract?
Agenda
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Blockchain 101
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Hash Previous block
Proof
Body
Hash of this block
Hash Previous block
Proof
Body
Hash of this block
Basic Block Structure
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Pointer to the previous block
A Time‐Ordered Chain
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Modify body
Recalculate ProofRecalculate Hash
Recalculate ProofRecalculate Hash
Recalculate ProofRecalculate Hash
Too resource consuming
A Time‐Ordered Chain Immutable
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Genesis Block 2 Block n
Block n +1
Block n +2
Block m
Block m +1
Block m + 2
Block n +1Block n +1
Block n + 2Block n + 2
Block m + 1Block m + 1
HeaderVersion numberPrevious Block HashTransaction Merkle RootTimestampDifficulty TargetNonce
BodyTransaction 1Transaction 2….
InputPrevious Transaction HashSender’s Public KeySignature by sender
OutputValueRecipient's public key
Bitcoin Structure
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• Immutable• Cannot modify the stored blocks• Self protected
• Perfect ledger structure • Ledger of timestamped transactions• Ledger of sequential transactions
• Control point• Addition of a new block to the chain• Who is the authority?
• The public, i.e. permissionless• Set of trusted entities, i.e. permissioned
Characteristics of Blockchain Ledger
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• Integrity• Digital signature offers the same feature
• Non tampering• Linked chain• Distributed block chain
• Chronological registration• Distributed• Undeniability and transparency
Some Advantages
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• Size of the ledger• linear increase with size O(n)
• Latency in transaction validation• Especially if permissionlessdistributed block chain• Bitcoin has a 50 mn latency
• Transparency• When confidentiality is needed
Some Disadvantages
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Mythology
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• Block chain• Ledger of chronological transactions
• Verification by navigating the list• Difficult to fool
• Bitcoin introduces some complexity• ANY BODY should be allowed to write to the chain block
• No centralized power
• This complexity may not be needed in all cases
Some Remarks
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• Blockchain ≠ Bitcoin or cryptocurrency• Blockchain does not need to have distributed permissionless consensus
• Cryptocurrency uses public distributed consensus• Land registry does not use public validation
• Blockchain does not need to be public• Blockchain does not need mining
• Proof of Work is only needed for permissionless blockchain
• Blockchain is not necessary slow and with latency• Bitcoin handles 7 transactions per second• Permissioned blockchains can be faster.
Some Misconceptions
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Consensus?
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TWO PROBLEMS:• How is a transaction validated?• How to synchronize the distributed ledgers?
Genesis Block 2 Block n
Block n +1
Block n +2
Block n +1Block n +1
Problem
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• Proof of Work• Proof of Stack• Byzantine Fault Tolerance• Federated Byzantine Agreement
Four Different Models
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• Solve the equation• Target is defined by Authority• Hash = SHA‐256
• Difficult to solve• Brute force calculation only
• Easy to verify• Challenge adjusts the average time to solve the equation• Number of miners• Total calculation power
Proof of Work
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• Why does it work?• Computationally costly to validate• Reward the validators• The likelihood that an attacker controls large chunk of the validators is small• Mining pools?
• Pros• Permissionless system
• Cons• Lot of wasted resources
• Power consumption of Ireland!• Latency• 51% attack• Large network of miners needed
Nakamoto, Satoshi. “Bitcoin: A Peer‐to‐Peer Electronic Cash System,” 2008. http://www.cryptovest.co.uk/resources/Bitcoin%20paper%20Original.pdf.
Proof of Work
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• Next block generator is polled deterministically with a function of its wealth (i.e., stake)
• If you own n% of the coins, you may expect to mint n% of the blocks
• Examples; PPCoin, Ethereum…• Coin age = amount x holding period• Bid coin ages
Proof of Stake
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• Why does it work?• the more you own of the system, the more you are expected to defend it
• Pros• Permissionless system• Less consuming than PoW
• Cons• Weaker trust model• Nothing at Stake attack• No established formally proven protocol
• No strong theory• Latency
King, Sunny, and Scott Nadal. “PPCoin: Peer‐to‐Peer Crypto‐Currency with Proof‐of‐Stake,” August 19, 2012. https://peercoin.net/assets/paper/peercoin‐paper.pdf.
Proof of Stake
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• Byzantine Fault = any failure of the system• Involuntarily such as a crash• Voluntarily such as a malicious behavior
• Byzantine fault tolerant system survives in case of Byzantine fault• n nodes• f ill‐behaving nodes• n‐f well‐behaving nodes• Optimal n=3f+1
Byzantine Fault
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• Why does it work?• Built to be resilient up to a given level
• Pros• Simple and robust• Well adapted to known set of trusted entities
• Trust is not linked to resources• Cons
• Not flexible• Pre‐established list of participants
• Sybil attack• All entities have the same trust level
Castro, Miguel, and Barbara Liskov. “Practical Byzantine Fault Tolerance.” In Proceedings of the Third Symposium on Operating Systems Design and Implementation. New Orleans, USA: USENIX Association, 1999. https://www.usenix.org/conference/osdi‐99/practical‐byzantine‐fault‐tolerance
Practical Byzantine Fault Tolerance (PBFT)
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• A quorum slice for node v is a set of nodes sufficient for v to decide that v decides to agree
• A quorum is a set of nodes necessary to reach an agreement• In PBFT, any 2 1 nodes form a quorum
• A FBA system can guarantee agreement if and only if any of 2 quorums share a node
• A two‐step validation process• Commitment ballot• Confirmation phase
Federated Byzantine Agreement (FBA)
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• Why does it work?• Formally proved• Distributed Byzantine decision
• Pros• Open membership• Each node decides who it trusts• Low latency
• Cons• Need to reach quorum intersection• Complex negotiation protocol
MAZIERES, DAVID. “The Stellar Consensus Protocol: A Federated Model for Internet‐Level Consensus,” July 14, 2015. http://www.the‐blockchain.com/docs/The%20Stellar%20Consensus%20Protocol%20‐%20A%20Federated%20Model%20for%20Internet‐level%20Consensus.pdf
Federated Byzantine Agreement (FBA)
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Smart Contracts?
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• A piece of software that is executed once a transaction is validated
• Some characteristics• Protected in integrity by the blockchain• Interpreted language with rather rich expressivity
• Announced to be THE solution • It is not simple in real world scenario
Smart Contract
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Theoretical Use Case: Managing All Contracts by a Blockchain
Contract (pdf) OCR
Smart Contract
NLP: Natural Language processing
Text to smart contract
(semantic/NLP)
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Use Case: What Could Go Wrong?
Contract (pdf) OCR
Text to smart contract
(semantic/NLP)
SmartContract
ETHEREUM JUN 16http://hackingdistributed.com/2016/06/16/scanning‐live‐ethereum‐contracts‐for‐bugs/
ETHEREUM JUNE 17https://www.reddit.com/r/ethereum/comments/6ettq5/statement_on_quadrigacx_ether_contract_error/
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• Ethereum and DAO• Hard fork on 17th July 2016 to recover the $40M theft from DAO
• Undermines immutability• Who decides to fork?
Hard Fork as a Remediation?
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Conclusion
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• Blockchain is a promising technology• Blockchain is larger than Bitcoin or Ethereum• Practical Federated Byzantine Agreement may be a more suitable consensus system for the M&E industry• At least for many scenarios
• Smart contracts may need some maturity• Tools for formal proof and test• Security model
Conclusion
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• Better understand the technology• Identify M&E problems that blockchain may solve
• Immutability• Distributed
• Design some heuristics to decide when to use blockchain• Experiment
Conclusion: What Next?
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Thank you for your attention! Merci
Any questions?