Slides de présentation du Prof. Jean-Luc Beuchat au eGov Workshop sur la signature électronique. Il traite de la signature électronique sous l'angle de l'innovation en présentant des cas d'intégration de la signature dans la blockchain. Jean-Luc Beuchat est professeur à l'institut informatique de gestion à la HES-SO Valais-Wallis à Sierre.

1. Digital Signature in the Blockchain
Jean-Luc Beuchat
Institute of Information Systems,
Techno-Pˆole 3, 3960 Sierre, Switzerland
jean-luc.beuchat@hevs.ch

2. Outline of the Talk
Background on Blockchain
Digital Signature in Bitcoin
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3. Blockchain in Switzerland – A Few Examples
2016 · · · · · ·•
The city of Zug is the first public entity in the world to accept
as payment option
2018 · · · · · ·•
Canton of Schaffhausen officially launches Procivis electronic
ID solution (timestamping on the blockchain)
2018 · · · · · ·•
Blockimmo (real estate tokenization platform) receives FINMA
approval that real estate shares can be purchased via
blockchain
2018 · · · · · ·• CMTA – Blueprint for tokenization
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4. Blockchain in Switzerland – A Few Examples
2019 · · · · · ·•
ZHAW and Swisscom announce the first qualified electronic
signature for blockchain
2019 · · · · · ·•
Several Swiss private banks enter blockchain asset
management market (Von Tobel, Falcon, Arab Bank
Switzerland, etc.)
2019 · · · · · ·• Switzerland’s first crypto banks (Sygnum and SEBA) receive
FINMA licences
2019 · · · · · ·• First prototype of the SIX Digital Exchange
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5. Outline of the Talk
Background on Blockchain
Digital Signature in Bitcoin
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6. Where the Story Begins
1978 · · · · · ·•
Public-key cryptography (R.L. Rivest, A. Shamir, and L.
Adleman)
1982 · · · · · ·•
Byzantine generals problem (L. Lamport, R. Shostak, and M.
Pease)
1982 · · · · · ·• Blind signatures for untraceable payments (D. Chaum)
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7. Chaum’s Blind Signature
The message author and the signer are different parties
• e-voting: voter and election authority
• Chaum’s untraceable payment: payer and mint (central authority)
A message is disguised before it is signed
Paper analog: carbon paper lined envelope
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8. Where the Story Begins
1997 · · · · · ·• Smart contracts (N. Szabo)
1998 · · · · · ·• b-money (W. Dai)
2002 · · · · · ·• Proof of work (A. Back)
2008 · · · · · ·• (S. Nakamoto)
2013 · · · · · ·• Ethereum (Vitalik Buterin)
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9. Background on Blockchain
Distributed database
Growing list of records (called blocks)
Blocks are secured and bound to each other using cryptography
Shared and immutable ledger (i.e. your wealth can’t be tampered with)
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10. Background on Blockchain
Permissionless blockchain
• Open and decentralized
• Everyone is allowed to create new blocks
• Truly public and easily verifiable
• Examples: , Ethereum
Permissioned blockchain
• Central authority
• Peers receive read and/or write privileges
• Examples: Hyperledger, Corda
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11. Background on Blockchain
Ability to reach consensus despite malicious nodes
Desired properties of a consensus algorithm
• Responsiveness
(drive to consensus at the pace of actual vs. maximum network delay)
• Communication complexity linear in the number of peers
Algorithm Responsiveness Linearity
Proof of work
NEO Delegated Byzantine fault tolerance
Libra HotStuff
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12. Outline of the Talk
Background on Blockchain
Digital Signature in Bitcoin
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13. Bitcoin Address
Short, alphanumeric string
Used to send and receive digital assets
Derived from a user’s public key
Example: 17khFNgJ4yk55agx9vjZbwTfHMHDHvFn7A
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14. Wallet
Stores your private key(s)
Hot wallet
• Connected to the internet
• Risky (zero-day, unpatched OS vulnerability, etc.)
Cold wallet
• USB drive or paper wallet in a safe deposit box
• Offline hardware wallet
Trezor
Ledger Nano S
Hardware Security Module (HSM)
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15. Bitcoin Transaction
Interaction between parties
Public entry in the blockchain
Unspent Transaction Output (UTXO)
• Indivisible chunk of
• Locked to a specific owner
• Scattered in the blockchain
• Transaction input: UTXO consumed by a transaction
• Transaction output: UTXO produced by a transaction
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16. Transaction Scripts
Script: scripting system for transactions
• Forth-like
• Stacked-based
• Intentionally not Turing-complete, with no loops
scriptPubKey (locking script)
• Encumbrance placed on an output
• Specifies the conditions that must be met to spend the output
• Usually contains a public key
scriptSig (unlocking script)
• Allows an UTXO to be spent
• Usually contains a digital signature
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17. Transaction Scripts
<PubKeyHash> EQUALVERIFY CHECKSIGDUP
Locking script (scriptPubKey)
HASH160
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18. Transaction Scripts
<PubKeyHash> EQUALVERIFY CHECKSIGDUP
Locking script (scriptPubKey)
HASH160DUP HASH160 <PubKeyHash> EQUALVERIFY CHECKSIG<sig> <PubKey>
Unlocking script (scriptSig)
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19. Transaction Scripts
<PubKeyHash> EQUALVERIFY CHECKSIGDUP
Locking script (scriptPubKey)
HASH160DUP HASH160 <PubKeyHash> EQUALVERIFY CHECKSIG<sig> <PubKey>
Unlocking script (scriptSig)
Execution pointer
<sig>
Stack
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20. Transaction Scripts
<PubKeyHash> EQUALVERIFY CHECKSIGDUP
Locking script (scriptPubKey)
HASH160DUP HASH160 <PubKeyHash> EQUALVERIFY CHECKSIG<sig> <PubKey>
Unlocking script (scriptSig)
Execution pointer
<sig>
Stack
<sig>
<PubKey>
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21. Transaction Scripts
<PubKeyHash> EQUALVERIFY CHECKSIGDUP
Locking script (scriptPubKey)
HASH160DUP HASH160 <PubKeyHash> EQUALVERIFY CHECKSIG<sig> <PubKey>
Unlocking script (scriptSig)
Execution pointer
<sig>
Stack
<sig>
<PubKey><PubKey>
<PubKey>
<sig>
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22. Transaction Scripts
<PubKeyHash> EQUALVERIFY CHECKSIGDUP
Locking script (scriptPubKey)
HASH160DUP HASH160 <PubKeyHash> EQUALVERIFY CHECKSIG<sig> <PubKey>
Unlocking script (scriptSig)
Execution pointer
<sig>
Stack
<sig>
<PubKey><PubKey>
<PubKey>
<sig>
<PubKeyHash>
<sig>
<PubKey>
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23. Transaction Scripts
<PubKeyHash> EQUALVERIFY CHECKSIGDUP
Locking script (scriptPubKey)
HASH160DUP HASH160 <PubKeyHash> EQUALVERIFY CHECKSIG<sig> <PubKey>
Unlocking script (scriptSig)
Execution pointer
<sig>
Stack
<sig>
<PubKey><PubKey>
<PubKey>
<sig>
<PubKeyHash>
<sig>
<PubKey><PubKey>
<PubKeyHash>
<PubKeyHash>
<sig>
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24. Transaction Scripts
<PubKeyHash> EQUALVERIFY CHECKSIGDUP
Locking script (scriptPubKey)
HASH160DUP HASH160 <PubKeyHash> EQUALVERIFY CHECKSIG<sig> <PubKey>
Unlocking script (scriptSig)
Execution pointer
<sig>
Stack
<sig>
<PubKey><PubKey>
<PubKey>
<sig>
<PubKeyHash>
<sig>
<PubKey><PubKey>
<PubKeyHash>
<PubKeyHash>
<sig>
<PubKey>
<sig>
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25. Transaction Scripts
<PubKeyHash> EQUALVERIFY CHECKSIGDUP
Locking script (scriptPubKey)
HASH160DUP HASH160 <PubKeyHash> EQUALVERIFY CHECKSIG<sig> <PubKey>
Unlocking script (scriptSig)
Execution pointer
<sig>
Stack
<sig>
<PubKey><PubKey>
<PubKey>
<sig>
<PubKeyHash>
<sig>
<PubKey><PubKey>
<PubKeyHash>
<PubKeyHash>
<sig>
<PubKey>
<sig>TRUE
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26. Pay to Script Hash (P2SH) Transaction
Script hash instead of public key hash in the locking script
The Recipient must provide
• A script matching the script hash
• Data which makes the script evaluate to true
M-of-N multisignature transaction
Locking scriptUnlocking script
<script><C sig><B sig>OP 0 HASH160 <script hash> EQUAL
<A pubkey> <B pubkey> <C pubkey> OP 3OP 2 CHECKMULTSIG
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27. Summary
Bitcoin uses digital signatures to prove ownership of UTXOs
Proof that you own the private key without having to reveal it
Keep your private key(s) offline (cold storage)
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28. Questions?
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29. References
S. Nakamoto. Bitcoin: A Peer-to-Peer Electronic Cash System. 2008.
https://bitcoin.org/bitcoin.pdf
A.M. Antonopoulos. Mastering Bitcoin. O’Reilly, 2014.
R. Wattenhofer. The Science of the Blockchain. Inverted Forest Publishing, 2016.
K. W¨ust and A. Gervais. Do you need a Blockchain? Cryptology ePrint Archive,
Report 2017/375.
D. Yaga, N. Roby, K. Scarfone. Blockchain Technology Overview. NISTIR 8202,
October 2018.
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