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Blockchain Fundamentals

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Talk at Bank Van Lanschot about Blockchain (Kortrijk, September 25, 2018).

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Blockchain Fundamentals

  1. 1. Blockchain Fundamentals by Bruno Lowagie Van Lanschot Kortrijk 25 September 18:30 iText booth, JavaOne, San Francisco
  2. 2. Warning! This is the “Understanding Blockchain” talk!
  3. 3. Table of Contents Concepts Bits & Bytes, Hashing, Encryption, Signatures, DLT,... Blockchain use cases Cryptocurrency  Bitcoin, Smart Contracts  Ethereum Your own blockchain When to use and when not to use, recipes for the future
  4. 4. Lots of theory, sorry… 1. Bits & Bytes 2. Transformations • Compression • Hashing • Encryption • Digital Signing 3. Distributed Ledger Technology • Blockchain • Consensus Part 1: Concepts
  5. 5. Before we start, I want to say: 01000111 01101111 01101111 01100100 00100000 01100101 01110110 01100101 01101110 01101001 01101110 01100111 00100001 Bay Bridge, San Francisco Bay Area
  6. 6. In hexadecimals: 47 6F 6F 64 20 65 76 65 6E 69 6E 67 21 San Francisco Bay
  7. 7. In hexadecimals: 47 6F 6F 64 20 65 76 65 6E 69 6E 67 21 Or, in a more human version: G o o d e v e n i n g ! San Francisco Bay
  8. 8. All information is transmitted, received, and stored as a sequence of zeros and ones 8 bits = 1 byte (today!) Initially: 1 byte = 6 bits ASCII: 7 bits needed IBM System/360: 8 bits Computers use binary code 0 1 1 0 0 0 0 1 Bits: Byte (Octet)
  9. 9. Encoding examples ASCII: American Standard Code for Information Interchange UTF-16: 16-bit Unicode Transformation Format B 66 0100 0010 42 r 114 0111 0010 72 u 117 0111 0101 75 n 110 0110 1110 6E o 111 0110 1111 6F ASCII: 브 10111110 00001100 BE 0C 루 10111000 11101000 B8 E8 노 10110001 01111000 B1 78 UTF-16:
  10. 10. Transformations Chihuly Garden and Glass, Seattle
  11. 11. Compression San Francisco
  12. 12. Compression Reduce the size in bytes without loss of information ▪ Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Facilisi morbi tempus iaculis urna id volutpat. Cras tincidunt lobortis feugiat vivamus at augue eget arcu dictum. Ac feugiat sed lectus vestibulum mattis. Hac habitasse platea dictumst quisque. - 318 bytes ▪ eNo9kFtOxUAMQ7fiBaDuASEhPthEOhOKpXm0k6TrJ/eC+IsS +1jO51zawdOio842F4wO6eovKHOYFlePBak8aYXjgDbm0bS mAcqwPitc+5lmjsLKGsMRjiZ74qH+i1Z0OYZAGq+QDe9S2G hEn2vnExEGSoncIlZKWXHPFn6Kb3hbYvBnxCOgzaR7Kr80D orj5i09CTlKHJHBR0bLKoHK4tE3vJZ/9aNAy3ppuNWce7T8Q RdP5IYPKfiWnS5mirOJq/xRzHEF7QrdfgBikHXp - 276 bytes, using LZW compression - Other compression algorithms: gzip, bzip2,…
  13. 13. Hashing Presidio, San Francisco
  14. 14. Hashing Creating a “message digest” A Cryptographic Hash function is a mathematical transformation algorithm that takes an input of arbitrary length (“message”) and returns a fixed-size byte sequence (the “message digest” or “hash”). Example: ▪ Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Facilisi morbi tempus iaculis urna id volutpat. Cras tincidunt lobortis feugiat vivamus at augue eget arcu dictum. Ac feugiat sed lectus vestibulum mattis. Hac habitasse platea dictumst quisque. - 318 bytes ▪ SHA-1, 160-bit (or 20 bytes): cc1b6a165b20e5d31f6ccac8eaff0bf64b95bffb ▪ SHA-256, 256-bit (or 32 bytes): a2ef46f63e8d8e093e1a263206692a973d332826a33e11270f37708c8c47faed
  15. 15. Use cases not limited to cryptographic hash functions ▪ Digital signatures ▪ Integrity check ▪ Random ID ▪ Session Cookies ▪ Hash tables ▪ Caching ▪ Passwords ▪ InterPlanetary File System (IPFS) ▪ … ▪ Blockchain!
  16. 16. Integrity check “fingerprint” of digital content ▪ Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Facilisi morbi tempus iaculis urna id volutpat. Cras tincidunt lobortis feugiat vivamus at augue eget arcu dictum. Ac feugiat sed lectus vestibulum mattis. Hac habitasse platea dictumst quisque. ▪ SHA-1, 160-bit (or 20 bytes): cc1b6a165b20e5d31f6ccac8eaff0bf64b95bffb ▪ Lorem ipsum dolor sit amet. consectetur adipiscing elit. sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Facilisi morbi tempus iaculis urna id volutpat. Cras tincidunt lobortis feugiat vivamus at augue eget arcu dictum. Ac feugiat sed lectus vestibulum mattis. Hac habitasse platea dictumst quisque. ▪ SHA-1, 160-bit (or 20 bytes): 04085fd6c91aa3f4a83ac4ee7d4eaf211acc0266
  17. 17. Confidential Document (e.g. proof of funds) Generate Hash AF1B4C...D34E Secure Server or Website Retrieve Hash AF1B4C...D34E Compare! Use case: integrity check
  18. 18. Requirements ▪ Deterministic: The same message always results in the same digest ▪ Irreversible: The output doesn’t contain any info about the input. E.g. Belgian National Number contains birth date and last digit indicates the gender  should be a hash! ▪ Collision resistant: It should be extremely difficult to find two inputs resulting in the same digest. Although it’s mathematically possible; e.g. with MD5 you “only” have 340,282,366,920,938,463,463,374,607,431,768,211,456 posible hash values (128 bit means 2128 combinations). ▪ Computationally efficient: It shouldn’t take a long time to compute the hash. ▪ Random output: It should be unpredictable, as if someone rolled dice. E.g. it should be very unlikely to get a hash like 0000000000000000000000000012345678abcdef
  19. 19. Types ▪ MD 5: Ron Rivest (broken) ▪ SHA: Secure Hashing Algorithm - SHA-1: NSA (broken: see https://shattered.io ) - SHA-2: NSA / NIST - SHA-3: Keccak (made in Belgium!) ▪ RIPEMD: KULeuven ▪ … These algorithms “age”: ▪ Flaws are discovered, e.g. SHA-1 deprecated by NIST in 2011 ▪ Computer power increases (brute force attacks)
  20. 20. shattered.io http://shattered.io/static/infographic.pdf
  21. 21. shattered.io Potentially impacted systems: Attack complexity Compared to other collision attacks http://shattered.io/static/infographic.pdf
  22. 22. Encryption Presidio, San Francisco
  23. 23. Can you read this? ▪ Tbbq Riravat! ▪ GHZO AQIIUES!
  24. 24. ▪ Rot13: move 13 letters down the alphabet ▪ Good Evening! ▪ 7 8 26 15 1 17 9 9 21 5 19! ▪ Good Evening! ▪ Tbbq Riravat! ▪ Ghzo Aqiiues! It’s easy if you have the key! 1. A 2. B 3. C 4. D 5. E 6. F 7. G 8. H 9. I 10. J 11. K 12. L 13. M 14. N 15. O 16. P 17. Q 18. R 19. S 20. T 21. U 22. V 23. W 24. X 25. Y 26. Z
  25. 25. Symmetric Encryption The same key is used for encryption and decryption 👤 👦👩 🔑 🔑 🔑 🔑 🔑 🔑
  26. 26. Asymmetric Encryption Keys come in pairs: one public key and one private key. What one key encrypts, only the other key can decrypt! Encryption: Signing:
  27. 27. Encryption Bob sends public key to Alice Alice encrypts message with public key Bob Bob receives encrypted message Bob decrypts message with private key 👦👩 🔑 🔑🔑 🔑 🔑
  28. 28. Some “name dropping” Some types are better for encryptions, others are better for signing. ▪ Public Key Cryptography Standards - PKCS#1: RSA Cryptography Standard (Rivest, Shamir, Adleman) - PKCS#7: Cryptographic Message Standard (CMS) - PKCS#11: Cryptographic Token Interface - PKCS#12: Personal Information Exchange Syntax Standard - PKCS#13: Elliptic Curve Cryptography Standard (ECDSA) ▪ National Institute of Standards and Technology (NIST) - AES: Advanced Encryption Standard (aka Rijndael) - Vincent Rijmen – Joan Daemen (Belgium!) ▪ Federal Information Processing Standards (FIPS) - DSA: Digital Signature Algorithm (DSA) ▪ European Telecommunications Standards Institute (ETSI) - CMS Advanced Electronic Signatures (CAdES) The size of the encrypted message depends on the size of the original message, the type of encryption, and the key length.
  29. 29. Digital Signatures Euronext Closing Bell, Brussels
  30. 30. What do we want to achieve? Authenticity (CA) Non- Repudiation Integrity Time of Signing (TSA) Long-Term Validation
  31. 31. Digital Signature 1. Integrity 2. Authentication 3. Non-Repudiation 👦👩 🔑 🔑🔑 🔑 signed by CA 🔑 ?
  32. 32. How it’s done in PDF • There are no bytes in the PDF that aren’t covered, other than the PDF signature itself. • The digital signature isn’t part of the ByteRange. • The concept “to initial a document” doesn’t exist; you sign the complete document at once, not on a page per page basis.
  33. 33. Serial Signatures A PDF can be signed more than once, but parallel signatures aren’t supported.
  34. 34. What’s inside the signature?
  35. 35. Long-Term Validation Signatures “age” - Certificates - Algorithms
  36. 36. Distributed Ledger Technology Oracle, Redwood Shores
  37. 37. “ Distributed Ledger Technology refers to a system to record and share data across multiple data stores (ledgers), which each have the exact same data records and are collectively maintained and controlled by a distributed network of computer servers, which are called nodes.
  38. 38. Centralized Decentralized Distributed
  39. 39. Centralized Decentralized Distributed
  40. 40. Centralized Decentralized Distributed
  41. 41. Distributed Ledger Technology DLT is a type of distributed database technology with the following characteristics: ▪ The records can be replicated over different nodes in a network (decentralized environment), ▪ New records can be added by each node, upon consensus reached by other nodes (ranging from one specific authoritative node to potentially every node), ▪ Existing records can be validated for integrity, authenticity, and non- repudiation, ▪ Existing records can’t be removed, nor can their order be changed, ▪ The different nodes can act as independent participants that don’t necessarily need to trust each other. Combined, these characteristics make DLT a great way to keep a ledger of records in a trustless environment.
  42. 42. Blockchain Caltrain station, Redwood City
  43. 43. “ hash Block 0 hash Block 1 hash Block 2 hash Block 3
  44. 44. node node node node node node Records are broadcasted over the network, with the goal to organize them in a block
  45. 45. node node node node node node Nodes need to reach consensus before they can add a block
  46. 46. node node node node node node When consensus is reached, all nodes add the same block
  47. 47. Blockchain types ▪ Permissionless versus permissioned: - Permissionless: no authorization or authentication needed - Permissioned: nodes must have a member identity; authorization and authentication is needed ▪ Public versus private: - Public: any node can join to read blocks and records, append records, and participate in the consensus mechanism - Private: only nodes that have been granted authority have that access ▪ Centralized, decentralized, distributed ledger control: - Centralized: one central server decides on the validation of a new block of records - Decentralized: a central authority delegates the validation of new blocks to a limited number of blocks - Distributed: all the nodes work together using a consensus mechanism
  48. 48. Consensus Great Indian Developer Summit, Tata Auditorium, Bengaluru, India
  49. 49. Byzantine Fault Tolerance Consensus needed: attack or retreat 🏰
  50. 50. Every general attacks If the majority vote is to attack 🏰
  51. 51. Every general retreats If the majority votes to retreat 🏰
  52. 52. Some attack, some retreat If there is a traitor among the generals 🏰
  53. 53. How to reach consensus? ▪ Proof of Work (PoW): - Example: Bitcoin ▪ Proof of Stake (PoS): - Example: Ethereum’s Casper the Friendly Finality Gadget (FFG)
  54. 54. Things you read about in the news papers 1. Bitcoin • Proof of Work: mining • Advantages • Disadvantages 2. Ethereum • Distributed Computing platform • Smart contracts • Proof of Stake Part 2: Blockchain use cases
  55. 55. Bitcoin Bull of Wall Street, New York
  56. 56. Bitcoin Cryptocurrency 👦👩 50 BTC Carol  10 BTC  Alice David  30 BTC  Alice Erin  20 BTC  Alice 🔑 B  50 BTC 🔑 A  9 BTC Sign hash with🔑A 1 BTC for the Miner who succeeds in solving the PoW puzzle and ensures Alice doesn’t spend a BTC twice Similar to lines in a ledger A has 60 BTC to spend 🔑A🔑 🔑B🔑 wallet wallet
  57. 57. https://www.quora.com/Whats-an-example-of-the-actual-data-stored-in-the-blockchain-for-a-Bitcoin-transaction/answer/Abhishek-Singh-7607 List of inputs • 0.00875314 BTC List of outputs • 0.00005885 BTC • 0.00868299 BTC Miner fee • 0.00001130 BTC Size: • Space required for transaction Fee Rate: • Amount the user is willing to spend for storage. Received time: • Broadcast time Mined time: • Time the transaction was stored Block hash: • Hash of the block the transaction is stored in
  58. 58. Bitcoin Mining Solving the puzzle in 10 minutes together! T1 T2 T3 T4 T5 T6 T7 TM hash hash hash hash hash hash hash 👤 miner Mike “Merkle Tree” proof 00000a5f4c8687d78ef…68b 40 leading bits must be zero: difficult! 240 attempts needed on average (~1 trillion) Testing proof is very easy Miner gets reward: • Sum of fees • Newly created coin
  59. 59. Bitcoin blocks
  60. 60. Bitcoin creation ▪ The system looks at the time to generate 2016 blocks: - If > 2 weeks: proof of work is made easier - If < 2 weeks: proof of work is made more difficult - 6 (1 hour) x 24 (1 day) x 14 (2 weeks): 2016 ▪ Miners get a reward if they succeed in solving the puzzle - Reward decreases over time - Cut in half every 210,000 blocks - About every 4 year (208 weeks) - Upper limit 21,000,000 BTC https://www.investopedia.com/tech/how-does-bitcoin-mining-work/ - Fractional coins exist: 0,00000001 BTC = 1 Satoshi (named after Satoshi Nakamoto)
  61. 61. On December 8, 2017, already16.7 million Bitcoins were created About 30% of those may be lost forever (hard drive crashes, misplaced private keys,…) https://coincentral.com/how-many-bitcoins-are-left/
  62. 62. Have you heard of… Owns… Expext to own… Cryptocurrencyhttps://think.ing.com/uploads/reports/ING_International_Survey_Mobile_Banking_2018.pdf Sample size: 14,828 15 countries minimum 1000 respondents / country (except Luxemburg)
  63. 63. How risky is owning one of the following asses, compared to cryptocurreny? https://think.ing.com/uploads/reports/ING_International_Survey_Mobile_Banking_2018.pdf
  64. 64. Advantages (some of which can also lead to disadvantages) ▪ Not controlled by any central authority (e.g. a bank, country,…) - Easy to make international payments, - The protocol can’t be manipulated by any person, organization, or government. - Not dependent on the political situation of a country,… (but other factors may influence the value of 1 BTC), ▪ The information is transparent - Everyone can see and verify all the transactions anytime, but only your public address is known, no personal info is visible, unless… ▪ Lower fees because there’s no “man in the middle” - In practice, there are BTC Exchange companies handling bitcoin transactions, e.g. Mt. Gox (Tokyo): RIP 2014 after announcing that 850,000 BTC ($450M) went missing.
  65. 65. Disadvantages Billboard, San Francisco
  66. 66. https://digiconomist.net/bitcoin-energy-consumption Bitcoin energy consumption Bitcoin network versus VISA network average consumption But aren’t we comparing apples with oranges? Bitcoin estimated to use 0.5% of the world’s electric energy by the end of 2018… and could someday consume 5% of the world's electricity The high cost of Proof of Work created new and original exploits, such as malware that uses your computer’s resources to mine bitcoins for hackers.
  67. 67. Disadvantages ▪ Exposure to fraud and scams - BTC Exchanges can be hacked, - Wallets can be lost (keys physically lost, keys stolen,…), ▪ No central authority is also a disadvantage - Use in black markets damages reputation, - No one can avoid “dump & pump”, - There is no buyer protection (e.g. credit card), ▪ Technical limits - Original bitcoin is slow - Proof of Work requires a lot of energy - May contain unexploited flaws - If you have 51% of the resources, you can corrupt the system - Could happen once miners stop mining if the reward drops ▪ High price volatility - Result of “dump & pump”; scandals (e.g. Mt. Gox) - many competing coins emerge; which one will “win”? - Everyone goes ICO, but who will deliver?
  68. 68. Ethereum Thiel Capital, San Francisco
  69. 69. “ Ethereum is an open-source, public, blockchain-based distributed computing platform and operating system featuring smart contract (scripting) functionality. Ether (ETH) is a cryptocurrency whose blockchain is generated by the Ethereum platform. Ether can be transferred between accounts and used to compensate participant mining nodes for computations performed.
  70. 70. Ethereum Virtual Machine ▪ The Ethereum Virtual Machine (EVM) is the runtime environment for smart contracts in Ethereum. Every Ethereum node in the network runs an EVM implementation and executes the same instructions. - Distributed Computing Platform - On February 1, 2018, there were 27,500 nodes in the main Ethereum network. ▪ Smart contracts: computer code that is executed on a distributed ledger - Smart contracts are high-level programming abstractions that are compiled down to EVM bytecode and deployed to the Ethereum blockchain for execution. - Ethereum's smart contracts are based on different computer languages, which developers use to program their own functionalities.
  71. 71. Predefined Contract • All counterparties agree on the terms (e.g. terms & conditions for a sale) • Known conditions for execution (e.g. 10% down-payment; full payment upon delivery) • Expressed in source code stored in the blockchain Events • An event triggers contract execution • An event can refer to: • The initiation of a transaction (e.g. a down-payment) • Information that is received (e.g. a parcel has been delivered) Execute • Terms of contract dictate movement of value based on conditions met • E.g. a down-payment: a parcel is sent in the real world • E.g. a parcel is received: the payment is processed Settlement • On-chain assets: e.g. cryptocurrency (for instance “paid with Bitcoin”) • Off-chain assets: e.g. the parcel (for instance “a work of art”) • The value bearing item resides outside (“off”) the blockchain; It has a digital counterpart in the blockchain (e.g. identified using an RFID tag) • Lifecycle events of the item are mirrored in the blockchain: the blockchain contains the “rights” (e.g. owner’s claim to a work of art) Smart contract: example
  72. 72. Coming soon: Proof of Stake Casper the Friendly Finality Gadget (FFG) (released on Github for review) ▪ Proof of Work: all miners work on a difficult puzzle ▪ Proof of Stake: the creator of the next block is chosen based on a criterium, e.g. the number of coin a miner owns. - miners are limited to mining a percentage of transactions that is reflective of their ownership stake. - For instance: a miner who owns 3% of the coin available can theoretically mine only 3% of the blocks. - You’d need 51% of all coin to corrupt the system - In the unlikely event you accumulate 51% of all coin, it’s not in your interest to make the system fail. ▪ Ethereum plans to move from PoW to PoS - Casper is a partial consensus mechanism combining proof of stake algorithm research and Byzantine fault tolerant consensus theory.
  73. 73. When, What to choose, Why 1. Do you need blockchain? 2. Which implementation? • MultiChain • Hyperledger project 3. Examples • T-Mining • iText • … Part 3: Your own blockchain
  74. 74. Do you need Blockchain? 10 questions to decide whether blockchain is the technology you need 1. Is it OK if the data is shared over all nodes? If not: NO BLOCKCHAIN 2. Is it OK if multiple identities can write? If not: NO BLOCKCHAIN 3. Is everyone known and trusted? If so: NO BLOCKCHAIN 4. Is having a central server necessary? If so: NO BLOCKCHAIN 5. Do you need to modify or erase data? If so: NO BLOCKCHAIN 6. Is performance critical? If so: MAYBE BLOCKCHAIN 7. Is data storage is going to be large? If so: MAYBE BLOCKCHAIN 8. Compliance with legal standards needed? If so: MAYBE BLOCKCHAIN 9. Are new participants free to enter? If so, 10. Can all participants validate? If so: PUBLIC PERMISSIONLESS BLOCKCHAIN If not: PUBLIC PERMISSIONED BLOCKCHAIN If not, 10. Can all participants validate? Is so: PRIVATE PERMISSIONLESS BLOCKCHAIN If not: PRIVATE PERMISSIONED BLOCKCHAIN
  75. 75. ▪ MultiChain by Coin Sciences Ltd. - For private blockchains ▪ Hyperledger project started by the Linux Foundation - Open source blockchains and tools: https://www.hyperledger.org/ - E.g. Hyperledger Fabric, contributed by IBM
  76. 76. Examples San Francisco Bay
  77. 77. Paper documents Digital documents Responsive content Dematerialization of paper Dematerialization of the document iText: What could threaten PDF?
  78. 78. How to make this an opportunity? ▪ Known flaws of data served to apps: - Reliability: was the data presented correctly? - Immutability: what if the data in the database changes? - Security: who has access to the data? ▪ Known flaws of PDF - Digital signatures are a pain - Signatures need to be applied sequentially - Certificate Authority (CA), Timestamp Authority (TSA) needed - Not all viewers support signatures (Preview, mobile viewers) - "Dark Data": it's difficult to unlock data from a PDF - We can solve this with tools - We're also working on "Next-Generation PDF" ▪ Enter blockchain: “A distributed database that serves as an irreversible and incorruptible repository for permanent records”
  79. 79. Storing the signature in the blockchain Digital signatures in PDF Digital signatures in Blockchain %PDF-1.5 … /ID[<8AA01A08CDAAF3F46E6E121898C8FEE7 > <EB4BDC9DA9206749952E4B89613D4658> ... 2 0 obj <<… /Type/Sig /Contents< > … >> … xref 0 81 0000000000 65535 f … trailer << … >> startxref 15787 %EOF DIGITAL SIGNATURE PDFDocument %PDF-1.5 … /ID[ <8AA01A08CDAAF3F46E6E121898C8FEE7> <EB4BDC9DA9206749952E4B89613D4658> ... URI: my.blockchain.com ... xref 0 81 0000000000 65535 f … trailer << … >> startxref 15787 %EOF Id: <8AA01A08CDAAF3F46E6E121898C8FEE7> <EB4BDC9DA9206749952E4B89613D4658> Value: DIGITAL SIGNATURE Metadata: URI, status PDFDocumentBlockchain
  80. 80. Information stored in the blockchain Document ID: [<ABCDEF>, <ABCDEF>] Timestamp Signed Document hash Compressed property list with metadata: - Status: e.g. “unpaid”, “paid” - Location(s) Certificate of signer • Identity • Public key
  81. 81. Advantages ▪ Criteria for signing are met: - Integrity - Authenticity - Non-Repudiation - Timestamp - LTV => renew registration ▪ Parallel signing is possible - Example: signing an NDA before a teleconference ▪ Make the existence of a document public, but not the content - Example: first-to-invent ▪ Updating metadata is possible - Example: avoid link-rot ▪ Due to the nature of IDs, related PDFs can be identified - Example: always read the latest version - Example: document processes can be automated
  82. 82. Adapted viewer Upon opening an invoice, the viewer can inform you: ▪ This document was registered in blockchain XYZ - Do you trust this blockchain? - Do you want to check the document in this blockchain? ▪ A blockchain service can return the following info: - The ID is not found: - This is a ghost invoice! - The ID is found, but the hash doesn’t correspond: - This is a forged invoice! - The ID is found and the hash corresponds: - This is a genuine invoice - It was originally signed by vendor ABC - Bank Van Lanschot registered it as paid
  83. 83. [<1234>,<5678>] SignedByBob[#DEF1] Status=quote [<1234>,<1234>] SignedByAlice[#ABCD] Status=quoterequestnode Alice (customer) node Bob (vendor) [<1234>,<5A6E>] SignedByAlice[#EF23] Status=accepted [<1234>,<ABCD>] SignedByAlice[#1234] Status=PO [<1234>,<5A6E>] SignedByCarol[#EF23] Status=shipment Carol (courier) node Dave (bank) node [<1234>,<F458>] SignedByDave[#B798] Status=paid Possible Application in Sales processes
  84. 84. Last Will & Testament ▪ Suppose that I write my last will and testament today, and I digitally sign it using today’s state-of-the-art technology, would my digital signature survive me? ▪ I surely hope not: - I hope I survive my signing certificate, - I hope I survive the time-stamping certificate, - I hope I survive the algorithms. ▪ A last will and testament is usually a document of which the content may change over time, and of which the content remains a secret until it needs to be executed. ▪ This is a good use case for blockchain.
  85. 85. <ABC, ABC>👦 <ABC, ABC> Service Provider Document storage (Adobe, Amazon, Box, Dropbox,...) Public Permissioned Blockchain <ABC, ABC> <ABC, XYZ> <ABC, XYZ> <ABC, XYZ><ABC, ABC> <ABC, XYZ> <ABC, XYZ> <ABC, XYZ> Smart contract: • Author or • Notary • Death certificate 👪
  86. 86. Bruno Lowagie mail: bruno@lowagie.com Web: https://lowagie.com Twitter: @bruno1970 iText headquarters, Gentbrugge

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