A block contains a series of transactions and reference to the previous block. It includes a block header and list of transactions. A blockchain is a distributed ledger that records transactions in an efficient, verifiable and permanent manner. It is open, decentralized with no single point of control, and ensures consistency across copies. Bitcoin uses blockchain technology for its cryptocurrency, operating in a decentralized peer-to-peer network without a central authority where anyone can participate anonymously.

2. WHAT IS BLOCK
• A block is a container data structure that contains a series of transactions.
• In Bitcoin – A block may contain more than 500 transaction on average, the
average size of a block is around 1 MB (proposed by Santoshi Nakamoto in
2010)
• May grow up to 8 MB or sometime higher
• There are two component in the block
• - Block Header
• List of Transaction

3. WHAT IS BLOCKCHAIN
A Blockchain is “an open , distributed ledger that can record
transactions between two parties efficiently and in a
verifiable and permanent way”
 The Keywords: Open(accessible to all)
• Distributed or Decentralized(no single party
Control)
• Efficient (Fast and scalable)
• Verifiable (everyone can check the validity of
information)
• Permanent(the information is persistent)

4. ANOTHER DEFINITION OF BLOCKCHAIN
• A Decentralised computation and information sharing plateform that enables
multiple
authorities domains , who do not trust each other , to cooperate , coordinate in a
rational decision making process.

5. CENTRALISED VS DECENTRALISED VS
DISTRIBUTED
• 1. Complete reliance on single point
• (centralised) is not safe.
• 2. Decentralised multiple point of
• collaboration
• 3. Distributed Everyone collectively
execute
• the job
Centralised Decentralised Distributed

6. A VERY SIMPLIFIED LOOK OF THE
BLOCKCHAIN
 Every node maintain a local copy of
the global datasheet.
The System ensure consistency
among the local copies
A. The local copies at every node is
identical
B. The local copies are always
updated based on the global
information

7. WE CALL THIS PUBLIC LEDGER
• A database of “historical information” available to everyone.
• For Example – The Transaction held between A to B of some rupees that can be updated to
every connected person of network which we see in next page of the slide
with some intresting picture.
o In this example the transaction is held between four person A , B , C , D.
An example of Public
Ledger From Banking Sectors

8. A B
D
A has 100$
A has 100$
A has $100
A has $100
C

9. A B
D
A has 100$
A has 100$
A has $100
A has $100
C
50$

10. A B
D
A has 100$
A has 100$ A has $100
A has $100
C
50$
A to B sent 50$
A to B sent $100 A to B sent $100
A to B sent 50$

11. A B
D
A has 100$
A has 100$ A has $100
A has $100
C
A to B sent 50$
A to B sent $100 A to B sent $100
A to B sent 50$
30$

12. A B
D
A has 100$
A has 100$ A has $100
A has $100
C
A to B sent 50$
A to B sent $100 A to B sent $100
A to B sent 50$
30$
B to D sent 30$ B to D sent 30$
B to D sent 30$ B to D sent 30$

13. A B
D
A has 100$
A has 100$ A has $100
A has $100
C
A to B sent 50$
A to B sent $100 A to B sent $100
A to B sent 50$
50$B to D sent 30$ B to D sent 30$
B to D sent 30$ B to D sent 30$

14. A B
D
A has 100$
A has 100$ A has $100
A has $100
C
A to B sent 50$
A to B sent $100 A to B sent $100
A to B sent 50$
50$B to D sent 30$ B to D sent 30$
B to D sent 30$ B to D sent 30$

15. BLOCKCHAINS AND PUBLIC LEDGERS
• Blockchain work like Public Ledger
• By this we ensure fallowing points…
• Protocols and Commitment: Ensure that every valid transaction from the
clientsarre commited and included in the blockchain within finite time.
• Consensus: Ensure that the local copies ae consistent and updated.
• Security – The data need to be tamper proof . Note that the clients may act
maliciously or can be compromised.
• Privacy and Authenticity – The data (or trasactions) belong to various clients,
Privacy and Authenticity needs to be ensured.

16. LET US SEE THE APPLICATION OF
BLOCKCHAIN
-BITCOIN-
 Bitcoin is a completely decentralised, peer-to-peer , Permissionless
cryptocurrency
putforth in 2009.
 Cryptocurency – A crptocurrency is a digital or virtual currency designed to work
as
a medium of exchange
 Completly decentraised : no single party for ordering or recording anything
 Peer-to-peer – software that runs on machine of all stakeholders to form the
system
 Permissionless – no identity , no need to signup anywhere to use , no access
control – anyone can participate in any role.

17. THANK YOU
o