The document discusses concepts related to blockchain technology, specifically the CAP theorem and the Byzantine Generals Problem, as presented in a lecture by Dr. Ferdinand Joe John Joseph at the Thai-Nichi Institute of Technology. The CAP theorem states that in a distributed database, only two of the three guarantees (consistency, availability, and partition tolerance) can be met at the same time, while blockchain focuses on availability and partition tolerance with some level of consistency. Additionally, the Byzantine Generals Problem illustrates the challenges of achieving consensus in distributed systems, applying this to blockchain's mechanism where all nodes must reach agreement despite potential corruption.

1. Blockchain Technology
Week 10
Unit IV – CAP Theorem, Byzantines General Problem
Ferdin Joe John Joseph, PhD
Faculty of Information Technology
Thai-Nichi Institute of Technology, Bangkok
Venue: D603

2. Week 10 – Unit IV
Agenda
• CAP Theorem
• Byzantines General Problem
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3. Hyper Encryption Standards

4. Features
• Symmetrical
• Key length of 57,000 to 200,000 bits
• No delimitation in number system
• Insensitive to factorize
• No semantics in cipher
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5. Visualization
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Plain Text DES Chiffre Hyper Encryption

6. Availability
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Highly Confidential
and Patented

7. Applications
• All applications of Banking
• Defense Technologies
• Telecommunication
• Health
• Plagiarism Protection
• Satellite Communication
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8. CAP Theorem

9. CAP Theorem
• Also known as Brewer’s Theorem
• Named after Computer Scientist Erik Brewer in 2002
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10. Theorem
• A distributed database can provide any two out of the three
gurantees only among those stated below.
1. Consistency: Every read receives the most recent write or an error
2. Availability: Every request receives a (non-error) response –
without the guarantee that it contains the most recent write
3. Partition tolerance: The system continues to operate despite an
arbitrary number of messages being dropped (or delayed) by the
network between nodes
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12. CAP Expanded
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C: Consistency – At any given time, all nodes in the network have
exactly the same (most recent) value.

13. CAP Expanded
• A: Availability – Every request to the network receives a response,
though without any guarantee that returned data is the most recent.
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14. CAP Expanded
• P: Partition tolerance – The network continues to operate, even if an
arbitrary number of nodes are failing.
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15. CAP Theorem Applied
• Due to the nature of distributed data stores (such as blockchain),
Partition tolerance is a given fact; there will always be
failing/unreachable nodes in the network (not least because of the
unstable nature of the internet). CAP Theorem states that one has to
choose between C (Consistency) or A (Availability) when in the
presence of P (Partition):
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16. Availability + Partition Tolerance
• Every request to the network receives a response, even if the
network cannot guarantee it is up to date due to network partitioning
(failing nodes).
• Choosing Availability over Consistency for a world-wide distributed
system will make it highly available, but its data will be out of date for
99.99% of the time. Furthermore, no-one will be able to guarantee
that the data returned is in fact the most recent.
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17. Availability + Partition Tolerance
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18. Consistency + Partition Tolerance
• The system will return an error or a time-out if particular information
cannot be guaranteed to be up to date due to network partitioning
(failing nodes).
• Choosing Consistency over Availability for a world-wide distributed
system will make it highly accurate, but it will most likely be
unavailable for 99.99% of the time.
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19. Consistency + Partition Tolerance
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20. Does Blockchain Violate CAP Theorem ?
• NO
• Those interested in blockchain, opt for AP (Availability + Partition) +
Strong/Eventual Consistency.
• This doesn’t mean Consistency used to the fullest.
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21. Byzantine Generals Problem

22. Byzantine General
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23. Byzantine - History
• Byzantine Empire, the eastern half of the Roman Empire, which
survived for a thousand years after the western half had crumbled
into various feudal kingdoms and which finally fell to Ottoman Turkish
onslaughts in 1453.
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24. Scenario
• Imagine that the grand Eastern Roman empire aka Byzantine empire
has decided to capture a city.
• The Byzantine army has completely encircled the city. The army has
many divisions and each division has a general.
• The generals communicate between each as well as between all
lieutenants within their division only through messengers.
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25. Attack Process
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Commander
Lieutenant 1 Lieutenant 2
“attack”“attack”
“He said ‘retreat’”
Lieutenant 2 is corrupt and consensus cannot be reached.

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Commander
Lieutenant 1 Lieutenant 2
“retreat”“attack”
“He said ‘retreat’”
Commander is corrupt and consensus cannot be reached.

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Commander
Lieutenant 1 Lieutenant 2 Lieutenant 3
“attack” “attack” “attack”
“attack” “retreat”

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Commander
Lieutenant 1 Lieutenant 2 Lieutenant 3
“attack” “retreat” “not sure”
“attack” “not sure”
“retreat” “retreat”
“attack”
“not sure”

30. How it applies to Blockchain
• Consensus Mechanism as it follows distributed mechanism
• In blockchain network, there is no commander
• Each node becomes a lieutenant and fall under equal hierarchy
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31. How it applies to Blockchain
• All participating nodes have to agree upon every message that is
transmitted between the nodes.
• If a group of nodes is corrupt or the message that they transmit is
corrupt then still the network as a whole should not be affected by it
and should resist this ‘Attack’.
• In short, the network in its entirety has to agree upon every message
transmitted in the network. This agreement is called as consensus.
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32. Practical Byzantine Fault Tolerance (PBFT)
• Faster
• Handle n Byzantine faults in a system with 3n+1 nodes
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33. PBFT Process
Request Preprepare Prepare Commit Reply
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34. PBFT by example
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Client Alpha
Bravo
Delta
Charlie

35. PBFT REQUEST
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Client Alpha
Bravo
Delta
Charlie

36. PBFT REQUEST
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Client Alpha
Bravo
Delta
Charlie

37. PBFT PRE PREPARE
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Client Alpha
Bravo
Delta
Charlie

38. PBFT PREPARE
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Client Alpha
Bravo
Delta
Charlie

39. PBFT PREPARE
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Client Alpha
Bravo
Delta
Charlie

40. PBFT COMMIT
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Client Alpha
Bravo
Delta
Charlie

41. PBFT REPLY
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Client Alpha
Bravo
Delta
Charlie

42. PBFT
Request Preprepare Prepare Commit Reply
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Client
Alpha
Bravo
Delta
Charlie

43. PBFT
Request Preprepare Prepare Commit Reply
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Client
Alpha
Bravo
Delta
Charlie

44. PBFT
Request Preprepare Prepare Commit Reply
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Client
Alpha
Bravo
Delta
Charlie

45. PBFT
Request Preprepare Prepare Commit Reply
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Client
Alpha
Bravo
Delta
Charlie

46. PBFT
Request Preprepare Prepare Commit Reply
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Client
Alpha
Bravo
Delta
Charlie

47. Next Week
• Peer to Peer Networking
• Distributed Computing
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