05 the blockchain technology 2019

1
The Blockchain
Technology
Please discontinue use of cell
phone and turn off ringer
Innovation & IT Management
Never before has humanity been so interested in a
database (Richard Cook, 2018).

2Nones, P. (March 18, 2018). Blockchain Technology: Hype … or Hope? https://nonesnotes.com/2018/03/18/blockchain-technology-
hype-or-hope/, last accessed July 25, 2018.
Introduction
2018

3
Most if not all the technologies that made the creation of the
blockchain possible existed at least 10 years earlier.
This includes
The Hashing algorithm (invented in 1953 Hans Peter Luhn)
The Internet (invented in 1969)
Asymmetric encryption (invented in 1976)1
Digital time stamping (invented in 1991)2
The proof of work (Back 2002)3
1. Diffie, W. and Hellman, M.E. (1976). New Directions in Cryptography, IEEE TRANSACTIONS ON INFORMATION THEORY, IT-22
(6). https://ee.stanford.edu/~hellman/publications/24.pdf, last accessed Mar 9, 2019.
2. Haber, S. and Stornetta, W.S. (1991). How to Time-Stamp a Digital Document, Journal of Cryptology, Vol. 3, No. 2, pp. 99–111.
3. Back, A. (2002). Hashcash - A Denial of Service Counter-Measure, http://www.hashcash.org/papers/hashcash.pdf , last accessed
Mar 9, 2019.
Cited by Pisa, M. and Juden, M. (2017). Blockchain and Economic Development: Hype vs. Reality. CGD Policy Paper. Washington,
DC: Center for Global Development. https://www.cgdev.org/publication/blockchain-and-economic-development-hype-vs-reality, last
accessed Feb 24, 2018.
Introduction

6
In December 1969, the first ARPANET maps were drawn. There
were only 4 nodes in the network.
December 1969
Introduction

7
June 1970, the network reached the east coast.
June 1970
Introduction

8
March 1972.
March 1972
Introduction

9
July 1977.
July 1977
Introduction

10
In March 1989 Tim Berners-Lee from the CERN created
what was to become known as the World Wide Web.
March 1989
Introduction

11
1993: The Internet went global connecting networks from several
countries, and continued expanding thereafter.
1993
Introduction

12
0:2
3
Coin Republic (Aug 30, 2013). Milton Friedman predicts the rise of Bitcoin in 1999!
https://www.youtube.com/watch?v=6MnQJFEVY7s, last accessed Mar 10, 2018.
Introduction

13
Being built around the Internet, while the fundamental principles
of the Internet are:
Introduction
Redundancy
Distribution (stronger than decentralization)
Redundancy
There are no:
Redundancy
There are no:
Third party
Redundancy
There are no:
Third party
Centralization

14Nakamoto, S. (2008). Bitcoin: A Peer-to-Peer Electronic Cash System, https://bitcoin.org/bitcoin.pdf, last accessed Mar 5, 2019.
Introduction - Bitcoin

15
It was in November 2008 that a paper
was published by Satoshi Nakamoto
describing blockchain and Bitcoin to
digitally send payments between any
two entities without the need for a
third-party.
Introduction
It was in November 2008 that a paper
was published by Satoshi Nakamoto
describing blockchain and Bitcoin to
digitally send payments between any
two entities without the need for a
third-party.
It is believed that Satoshi Nakamoto
was the name adopted by the person
or group of people who created
bitcoin and the concept of the
blockchain.

16
They also devised the first blockchain
database, and validated the first block
ever on January 3, 2009.
CuriousInventor (Jul 14, 2013). How Bitcoin Works Under the Hood, https://www.youtube.com/watch?v=Lx9zgZCMqXE, last
accessed Aug 21, 2017.
This block has come to be known as
the genesis block.
Introduction

17
Introduction
igotbitcoin (n.d.). Newsweek Misidentifies Bitcoins Creator As Dorian Nakamoto, http://www.igotbitcoin.com/milestones/, last
accessed Nov 26, 2017.

18igotbitcoin (n.d.). Newsweek Misidentifies Bitcoins Creator As Dorian Nakamoto, http://www.igotbitcoin.com/milestones/, last
Introduction

192:4igotbitcoin (n.d.). Newsweek Misidentifies Bitcoins Creator As Dorian Nakamoto, http://www.igotbitcoin.com/milestones/, last
2:4
7
Introduction

22
There are more than 1.658 cryptocurrencies in the world, all of
which comprising what we call Altcoins.
Introduction

23
Introduction

240:0
Today there are more than 1500 blockchain based systems:
Introduction

25
Introduction

26https://blockexplorer.com/block/000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
Introduction: www.blockexplorer.com

27

29
Introduction
The number of bitcoin transactions per day:
Source: https://www.blockchain.com/fr/charts/n-transactions, July 22, 2018.
490,544
229,480

30Source: https://www.blockchain.com/fr/charts/n-transactions, Apr 28, 2019.
404,279
Introduction
The number of bitcoin transactions per day (cont’d):

31Source https://www.blockchain.com/charts/market-price, July 22, 2018.
Introduction
Bitcoin market price:

32
Blockchain defined
A blockchain is a data structure that makes it possible to create a
digital ledger of transactions and share it among a distributed
network of computers.
Nash, K.S. (2016-07-14). IBM Pushes Blockchain into the Supply Chain, Wall Street Journal, https://www.wsj.com/articles/ibm-
pushes-blockchain-into-the-supply-chain-1468528824, last accessed Aug 24, 2017.
Ledgers have been used in
double-entry bookkeeping since
the 13th century.
Thanks to IT, 21st century ledgers
are shared and distributed.
As such, they become an
immutable record of all trans-
actions on the network, a record
that all network participants can
access.

34
Blockchain defined
Ledgers have been used in
double-entry bookkeeping since
the 13th century.
Thanks to IT, 21st century ledgers
are shared and distributed.
As such, they become an
immutable record of all trans-
actions on the network, a record
that all network participants can
access.

35
Blockchain defined
The difference between decentralized and distributed :
Centralized Decentralized Distributed

36
At a very high level, the blockchain is a decentralized ledger, or
list, of all transactions across a peer-to-peer network. This is the
technology underlying Bitcoin and other cryptocurrencies, and it
has the potential to disrupt a wide variety of business processes.
PwC (January 2016). Q&A: What is blockchain? http://www.pwc.com/us/en/financial-services/publications/viewpoints/assets/qa-
what-is-blockchain.pdf,last accessed Aug 24, 2017.
Blockchain defined
IBM (May 9, 2016). IBM Blockchain on Bluemix is now Beta! https://www.ibm.com/blogs/internet-
https://www.ibm.com/blogs/bluemix/2016/05/blockchain-on-bluemix-now-beta/, last accessed Aug 24, 2017.

39
txn 555…
txn ab3…
txn ba2…
txn ab3…
txn ba2…
txn 902…
Pool of unconfirmed transactions
A
B

40
Question:
How do we know that the message between A and B is valid?
i.e., that it is A that initiated the transaction?
The role of cryptography
Question:
How do we know that the message between A and B is valid?
i.e., that it is A that initiated the transaction?
Answer:
Through cryptography. Namely asymmetric encryption.

41
This includes
Mar 9, 2019.
Introduction

42
A key is a string of bits.
DI Management (not dated). An Introduction to Using Keys in Cryptography, http://www.di-mgt.com.au/cryptokeys.html, last
accessed July 25, 2013.
1111 1110 1101 1100 1011 1010 1001 1000 0111 0110 …. 0101
A 256-bit key will have exactly 256 bits in it, i.e. 32 bytes
To make it less cumbersome, keys can also be written in
hexadecimal format where each character represents 4 bits,
e.g.:
FE1CBA98765432100123456789ABCDEF
which represents 16 bytes or 128 bits.
Expressed in bits, the above example yields this string:
11111110 00011100 10111010 10011000 01110110 01010100
00110010 00010000 00000001 00100011 01000101 01100111
10001001 10101011 11001101 11101111
A 256-bit key will have exactly 256 bits in it, i.e. 32 bytes (32x8).

43
1111 1110 1101 1100 1011 1010 1001 1000 0111 0110 …. 0101
A 256-bit key will have exactly 256 bits in it, i.e. 32 bytes
e.g.:
FE1CBA98765432100123456789ABCDEF
11111110 00011100 10111010 10011000 01110110 01010100
00110010 00010000 00000001 00100011 01000101 01100111
10001001 10101011 11001101 11101111
1111

44
1111 1110 1101 1100 1011 1010 1001 1000 0111 0110 …. 0101
e.g.:
FE1CBA98765432100123456789ABCDEF
11111110 00011100 10111010 10011000 01110110 01010100
00110010 00010000 00000001 00100011 01000101 01100111
10001001 10101011 11001101 11101111
1111 0001

45
1111 1110 1101 1100 1011 1010 1001 1000 0111 0110 …. 0101
e.g.:
FE1CBA98765432100123456789ABCDEF
11111110 00011100 10111010 10011000 01110110 01010100
00110010 00010000 00000001 00100011 01000101 01100111
10001001 10101011 11001101 11101111
1111 0001 1111

46
Key Size Possible Key Combinations
2-bit 22 =4
3-bit 23 =8
4-bit 24 =16
5-bit 25 =32
. . . .
. . . .
40-bit 240 =1099511627776
. . .
. . . .
56-bit 256 =72057594037927900
. . . .
. . . .
64-bit 264 =18446744073709600000
. . . .
. . . .
128-bit 2128 =340282366920938000000000000000000000000

47
Key Size Possible Key Combinations
2-bit 22 =4
3-bit 23 =8
4-bit 24 =16
5-bit 25 =32
. . . .
. . . .
40-bit 240 =1099511627776
. . .
. . . .
56-bit 256 =72057594037927900
. . . .
. . . .
64-bit 264 =18446744073709600000
. . . .
. . . .
128-bit 2128 =340282366920938000000000000000000000000

48
3-bit 23 =8
4-bit 24 =16
5-bit 25 =32
. . . .
. . . .
40-bit 240 =1099511627776
. . .
. . . .
56-bit 256 =72057594037927900
. . . .
. . . .
64-bit 264 =18446744073709600000
. . . .
. . . .
128-bit 2128 =340282366920938000000000000000000000000
* 200 computers working simultaneously.

49
Asymmetric Encryption
The private key
For every user, a pair of private
and public keys are created, which
go hand in hand but are totally
independent one from the other
The public key

50
The private key
The public key
Like a jigsaw

51
B’s public key
751A696
C24D970
10121261
Transaction
B’s private key
751A696
C24D970
10121261
Encrypted
message
Encrypted
message
A encrypts his message using
B’s public key.
Upon reception, B decrypts the
message with his private key.
A
B
A pair of keys are used: a public key, which encrypts data,A pair of keys are used: a public key, which encrypts data,
and a corresponding private, or secret key for, decryption.
A pair of keys are used: a public key, which encrypts data,
and a corresponding private, or secret key for, decryption.
The public key is published to the world while the private
key is kept secret.

52
A to John
A to Leila
A to Abdu
A to Haykel
A to Shakti
5 BTC
12 BTC
2000 BTC
143 BTC
10 BTC
04344244233344454778877..999
12443444543344454773344..877
44450434447733244234541..123
12443444543344454773344..877
75444788332443443344774..181
Even though all these transactions have been signed by A, the
digital signature is different every time because the recipient is
different every time.

53
From the movie Eyes Wide Shut (Stanley Kubrick, 1999) @1:07:28.
0:2
7
Asymmetric Encryption – An Example

54

55
The public keys are stored in
public servers accessible to
everyone.
everyone.
Since there is only one key (the
private key) which goes hand in
hand with the public key, the risk
to decipher an encrypted
message is reduced
everyone.
Since there is only one key (the
private key) which goes hand in
hand with the public key, the risk
to decipher an encrypted
message is reduced because it
is almost impossible to generate
a private key from the public
key.

56
Asymmetric Encryption – Another Example

58
txn 555…
txn ab3…
txn ba2…
txn ab3…
txn ba2…
txn 902…
A
B

59
The transaction, along many others, when
confirmed, is collected in a block.
The block is broadcast to all nodes in the P2P
network.
A
B
Blockchain defined

60
Existing blockchain
A new block
Time

61
A
B
Parties validate the block in which the transaction was inserted
through a process called mining.
Blockchain defined
through a process called mining.
It is therefore once the transactions are approved, that the new
block is added to the blockchain, which is a ledger of all past
transactions.

62
Existing blockchain
Once the block has been added, it is linked to the one before it,
and the one after it (hence the word chain).
The ledger balances are updated to reflect the new balances
for all parties.
Blockchain defined

63
Existing blockchain
for all parties.
The process goes on and a new block is formed every 10mn,
with a new set of transactions, all having occurred at about the
same time.
Blockchain defined

65
Existing blockchain
for all parties.
The process goes on and a new block is formed every 10mn,
with a new set of transactions, all having occurred at about the
same time.
A blockchain is thus a linked list of blocks, each block
containing transactions.
Each block is limited to 2,400 transactions (~ 1Mb).
3Blue1Brown (Jul 7, 2017). Ever wonder how Bitcoin (and other cryptocurrencies) actually work?,
https://www.youtube.com/watch?v=bBC-nXj3Ng4, last accessed Aug 23, 2017.
Blockchain defined

66
206 Gb107 Gb 2 years earlier
Blockchain defined

67
A
B
Remember that everyone has a copy of the blockchain.
If anyone tries to alter it to claim ownership of currency that is
not really theirs, the discrepancy is immediately obvious to
everyone.
Hinchcliffe, D. (July 31, 2015). How blockchain is likely to transform IT and business, ZDNet,
http://www.zdnet.com/article/how-blockchain-is-likely-to-change-it-and-business-forever/, last accessed Aug 20, 2017.
Blockchain defined

68
Remember that everyone has a copy of the blockchain.
If anyone tries to alter it to claim ownership of currency that is
not really theirs, the discrepancy is immediately obvious to
everyone.
Hinchcliffe, D. (July 31, 2015). How blockchain is likely to transform IT and business, ZDNet,
http://www.zdnet.com/article/how-blockchain-is-likely-to-change-it-and-business-forever/, last accessed Aug 20, 2017.
Blockchain defined
through a process called mining performed by the miners.

69
Question:
Who are the miners?
Mining and the miners

70
Question:
Who are the miners?
Question:
Who are the miners and what do they do?
Question:
Answer:
A
B

71
Question:
Answer:
Miners are individuals who provide the computing power for
Bitcoin’s validation process.
They use this computing power by solving a cryptographic
problem, called a hash function.
By using their computing power for this work, miners are
rewarded with bitcoins.
Wan, T. and Hoblitzell, M. (June 26, 2014). Bitcoin - Fact. Fiction. Future, https://dupress.deloitte.com/dup-us-en/topics/emerging-
technologies/bitcoin-fact-fiction-future.html, last accessed Aug 20, 2017.
Question:
Answer:
In fact, that is how new bitcoins enter the money supply
(more about this later).

72
Question:
Answer:
Stanley, J. (February 5, 2018).Blockchain Explained: How It Works, Who Cares and What Its Future May Hold,
https://www.techspot.com/article/1567-blockchain-explained/, last accessed Feb 5, 2018.
Question:
Answer:
In fact, that is how new bitcoins enter the money supply
(more about this later).
An essential feature of blockchain is its ability to encrypt each
“block” of data for a unique hash output that is also stamped onto
the succeeding block, creating a chain of sequential information
which is then verified through a consensus of activity across a
network of participants.

73
This includes
Mar 9, 2019.
Introduction

75
SHA256
is a 64 character long chain considered a fingerprint for the
data.
Hash function - SHA256

78
SHA256 - http://passwordsgenerator.net/sha256-hash-generator/

79

80

81

82
Imagine that you’d want to look up a telephone number
in a database. Hans Peter Luhn
Given the 8-digit number 23 15 26 52, an algorithm could
simply sequentially search through the database until it found it.
In a database of millions though, this could be time consuming.
Paolini-Subramanya, M. (Feb 6, 2018). The Invention of the Hashing Algorithm, https://medium.com/@dieswaytoofast/the-invention-
of-the-hashing-algorithm-600933d7f845, last accessed Apr 9, 2019.
Luhn’s had a better: The phone number’s digits were grouped
into pairs (in this case, 23, 15, 26, 52). The paired digits were
then added together (5, 6, 8, 7), from which a new number was
generated, consisting of each single-digit result. The original
phone number and the name or address corresponding to it
would then be put into a bucket labeled 5687.

83
Given the 8-digit number 23 15 26 52
5, 6, 8, 7

84
5, 6, 8, 75, 6, 8, 7
11
5, 6, 8, 7
11 15
5, 6, 8, 7
11 15
2
5, 6, 8, 7
11 15
2 6
5, 6, 8, 7
11 15
2 6
8

85
21 11 10 1121 11 10 11
20 11 21 01
21 11 10 11
20 11 21 01
10 00 32 11
21 11 10 11
20 11 21 01
10 00 32 11
21 22 00 10
21 11 10 11
20 11 21 01
10 00 32 11
21 22 00 10
21 10 11 11
21 11 10 11
20 11 21 01
10 00 32 11
21 22 00 10
21 10 11 11
20 21 11 01

86
Looking up an entry from a phone number involved quickly
calculating the bucket number using Luhn’s method and then
retrieving the information from that bucket.

87
Infinite number
of values 2256 values
It is “impractical” to revert thanks to the concept of “information
destruction”. Of the result of the calculation, we only take the
rightmost digits (256 of them).

88
So,
Hash of “1235566” is (for example): 0100010001…0001
So,
So,
We strike out the first 4 digits : 0100010001…0001
So,
and we obtain: 010001…0001
So,
Hash of the file “Syllabus ITM 301”: 1111010001…0001

89
Inspired from The Economist (Oct 31st 2015).The great chain of being sure about things,
https://www.economist.com/news/briefing/21677228-technology-behind-bitcoin-lets-people-who-do-not-know-or-trust-each-other-
build-dependable, last accessed Jan 4, 2018.

90
Inspired from The Economist (Oct 31st 2015).The great chain of being sure about things,
https://www.economist.com/news/briefing/21677228-technology-behind-bitcoin-lets-people-who-do-not-know-or-trust-each-other-
build-dependable, last accessed Jan 4, 2018.

91
Merkle R.C. (1988) A Digital Signature Based on a Conventional Encryption Function. In: Pomerance C. (eds) Advances in
Cryptology — CRYPTO ’87. CRYPTO 1987. Lecture Notes in Computer Science, vol 293. Springer, Berlin, Heidelberg,
https://people.eecs.berkeley.edu/~raluca/cs261-f15/readings/merkle.pdf, last accessed Apr 7, 2019.
Ralph C. Merkle, born in 1952, computer scientist, is
one of the inventors of public key cryptography and
the inventor of cryptographic hashing.
Ralph Merkle

92See 28Bitcoin-101-Merkle-Roots-and-Merkle-Trees-Bitcoin-Coding-and-Software-The-Block-Header-720p
https://blockexplorer.com

93
Block no.
286819

94
Block no.
286819

95
99 transactions each with a Hash

96
Ken Shirriff’s blog on
http://www.righto.com/2014/02/bitcoin-mining-hard-way-algorithms.html:

97

98

99
import hashlib
# Hash pairs of items recursively until a single value is obtained
def merkle(hashList):
if len(hashList) == 1:
return hashList[0]
newHashList = []
# Process pairs. For odd length, the last is skipped
for i in range(0, len(hashList)-1, 2):
newHashList.append(hash2(hashList[i], hashList[i+1]))
if len(hashList) % 2 == 1: # odd, hash last item twice
newHashList.append(hash2(hashList[-1], hashList[-1]))
return merkle(newHashList)
def hash2(a, b):
# Reverse inputs before and after hashing
# due to big-endian / little-endian nonsense
a1 = a.decode('hex')[::-1]
b1 = b.decode('hex')[::-1]
h = hashlib.sha256(hashlib.sha256(a1+b1).digest()).digest()
return h[::-1].encode('hex')
# https://blockexplorer.com/rawblock/0000000000000000e067a478024addfecdc93628978aa52d91fabd4292982a50
txHashes = [
"00baf6626abc2df808da36a518c69f09b0d2ed0a79421ccfde4f559d2e42128b",
"91c5e9f288437262f218c60f986e8bc10fb35ab3b9f6de477ff0eb554da89dea",
"46685c94b82b84fa05b6a0f36de6ff46475520113d5cb8c6fb060e043a0dbc5c",
"ba7ed2544c78ad793ef5bb0ebe0b1c62e8eb9404691165ffcb08662d1733d7a8",
"b8dc1b7b7ed847c3595e7b02dbd7372aa221756b718c5f2943c75654faf48589",
"25074ef168a061fcc8663b4554a31b617683abc33b72d2e2834f9329c93f8214",
"0fb8e311bffffadc6dc4928d7da9e142951d3ba726c8bde2cf1489b62fb9ebc5",
"c67c79204e681c8bb453195db8ca7d61d4692f0098514ca198ccfd1b59dbcee3",
Shirriff’s Python code

100
import hashlib
# Hash pairs of items recursively until a single value is obtained
def merkle(hashList):
if len(hashList) == 1:
return hashList[0]
newHashList = []
# Process pairs. For odd length, the last is skipped
for i in range(0, len(hashList)-1, 2):
newHashList.append(hash2(hashList[i], hashList[i+1]))
if len(hashList) % 2 == 1: # odd, hash last item twice
newHashList.append(hash2(hashList[-1], hashList[-1]))
return merkle(newHashList)
def hash2(a, b):
# Reverse inputs before and after hashing
# due to big-endian / little-endian nonsense
a1 = a.decode('hex')[::-1]
b1 = b.decode('hex')[::-1]
h = hashlib.sha256(hashlib.sha256(a1+b1).digest()).digest()
return h[::-1].encode('hex')
# https://blockexplorer.com/rawblock/0000000000000000e067a478024addfecdc93628978aa52d91fabd4292982a50
txHashes = [
"00baf6626abc2df808da36a518c69f09b0d2ed0a79421ccfde4f559d2e42128b",
"91c5e9f288437262f218c60f986e8bc10fb35ab3b9f6de477ff0eb554da89dea",
"46685c94b82b84fa05b6a0f36de6ff46475520113d5cb8c6fb060e043a0dbc5c",
"ba7ed2544c78ad793ef5bb0ebe0b1c62e8eb9404691165ffcb08662d1733d7a8",
"b8dc1b7b7ed847c3595e7b02dbd7372aa221756b718c5f2943c75654faf48589",
"25074ef168a061fcc8663b4554a31b617683abc33b72d2e2834f9329c93f8214",
"0fb8e311bffffadc6dc4928d7da9e142951d3ba726c8bde2cf1489b62fb9ebc5",
"c67c79204e681c8bb453195db8ca7d61d4692f0098514ca198ccfd1b59dbcee3",
99 transaction Hashes
Shirriff’s Python code

101Antonopoulos, A.M. (Jan 31, 2016). Consensus Algorithms, Blockchain Technology and Bitcoin UCL,
https://www.youtube.com/watch?v=fw3WkySh_Ho, last accessed Aug 23, 2017.
In 1997 Adam Back created a system for antispam
called hashcash.
The concept of hashcash
Hashcash is an algorithm that requires a sizeable amount of
work to compute.
work to compute.
For an email, for example, a hashcash stamp is added to
the header of the message to prove that the sender has
expended a modest amount of CPU time calculating the stamp
prior to sending the email.
work to compute.
For an email, for example, a hashcash stamp is added to
the header of the message to prove that the sender has
expended a modest amount of CPU time calculating the stamp
prior to sending the email.
Adam Back figured that this mechanism will make spammers
do some work: a few hundred thousand SHA operations in a
row, which, by definition, produce a fingerprint with a specific
value that proves that a certain amount of work was done.

102
This includes
Mar 9, 2019.
Introduction

103
Why don’t spammers like this concept?
For example, consider that to send an email, you have to spend
half a second of computing.
If you are a spammer, and you want to send a million
messages, you will have to do half a million seconds of
computing! (a million times .5s).
That is a lot of work.
That is a lot of work.
In Back’s rationale, if the sender goes through some amount of
time and effort to generate the stamp and send the email, it is
unlikely that they are a spammer.

104
0:1
0
WatchMojo.com (May 27, 2014). Top 10 Bitcoin Facts, https://www.youtube.com/watch?v=2UC_8NdR1To, last accessed Nov 6,
2017.

105
Question:
How do miners validate the new transactions?
Antonopoulos, A.M. (Jan 31, 2016). Consensus Algorithms, Blockchain Technology and Bitcoin UCL,
https://www.youtube.com/watch?v=fw3WkySh_Ho, last accessed Aug 23, 2017.
Question:
Answer:
1. Every 10 minutes, they look at a set of unconfirmed
transactions and see whether
a. The transactions conform to some consensus rules (private/public
keys, never has been spent previously, output ≤ input, etc.).
b. The block conforms to some consensus rules (block size, reward is
not spent in less than 100 blocks, etc.).
Question:
Answer:
1. Every 10 minutes, they look at a set of unconfirmed
transactions and see whether
a. The transactions conform to some consensus rules (private/public
keys, never has been spent previously, output ≤ input, etc.).
b. The block conforms to some consensus rules (block size, reward is
not spent in less than 100 blocks, etc.).
2. They then race to bundle data from the last block in the
ledger and data in the current block, by finding a number
called nonce. number used oncenumber
nonce
number used oncen once

107
Answer (cont’d):
3. Then they compute the hash to produce a unique fingerprint
making the block and its transactions valid and verifiable.
Answer (cont’d):
4. The hashed block must have a set number of zeroes at the
beginning. So the miner has to try different nonces to find
the right value.
Answer (cont’d):
the right value.
5. When a miner finds a hash with the correct number of
zeroes, the discovery is broadcast to the rest of the network.

108
Mining and the miners - Facts
The miner’s task: Apply the hash (SHA256) so that:
SHA256 (current and previous blocks + nonce) < Target
(i.e., starts with n zeroes).
For example: it starts with 4 zeroes.
For example: it starts with 4 zeroes, like 0000126GhghhG1jkjj6èè-
For example: it starts with 4 zeroes, like 0000126GhghhG1jkjj6èè-
For bitcoin, the nonce lies between 0 and 4.294.967.296.
All hashes begin with zeroes; at least 8 and up to 63.
Currently the number of zeroes is around 17 (on the average).

109Inspired by CuriousInventor (Jul 14, 2013). How Bitcoin Works Under the Hood,
https://www.youtube.com/watch?v=Lx9zgZCMqXE, last accessed Aug 21, 2017.
To find the nonce, a computer needs to perform approximately an
average of 10²¹ operations.
Previous
s

110
Previous
The amount of processing performed to find the target is what
constitutes the proof-of-work (PoW).
All target hashes begin with 0s--at least eight 0s, and up to 63 0s.
There is a maximum target set by the Bitcoin Protocol.
No target can be greater than this number:
0000 0000 ffff ffff ffff ffff ffff ffff ffff ffff ffff ffff ffff ffff ffff ffff
Inspired by CuriousInventor (Jul 14, 2013). How Bitcoin Works Under the Hood, https://www.youtube.com/watch?v=Lx9zgZCMqXE,
last accessed Aug 21, 2017 and Hong, E. (Oct 17, 2017). Read more: How Does Bitcoin Mining Work? Investopedia,
s

111
SHA256
is random but deterministic
finding its inverse is nearly impossible
SHA256
what are the chances the first bit is going to be zero?
50%
SHA256
50%
2 bits?
25%
SHA256
50%
2 bits?
25%
10 bits?
1
2 𝑛

112
SHA256
50%
2 bits?
25%
10 bits?
nearly impossible
How?

1133Blue1Brown (Jul 7, 2017). Ever wonder how Bitcoin (and other cryptocurrencies) actually work?
For example, for 60 zeroes:

114Inspired by CuriousInventor (Jul 14, 2013). How Bitcoin Works Under the Hood,
https://www.youtube.com/watch?v=Lx9zgZCMqXE, last accessed Aug 21, 2017 and Hong, E. (Oct 17, 2017). Read more: How
No target can be greater than this number:
0000 0000 ffff ffff ffff ffff ffff ffff ffff ffff ffff ffff ffff ffff ffff ffff

115
Digital Signatures
A B
A computes the hash of
the message she is
sending
B receives the hashcode of the
message crypted with A’s private
key
The hashcode obtained is
then crypted with A’s
private key
key AND
key AND
the original message

116
Digital SignaturesThe hashcode obtained is
then crypted with A’s
private key

117
B checks whether A’s
public key
B computes the message’s hash
again
public key matches her
private key

118
public key
again
private key
Get the hash value
of the message
Signature is
valid when
values are
equal

119
public key
again
private key
Get the hash value
of the message
Signature is
valid when
values are
equal

120
Digital Signatures
Get the hash value
of the message
Signature
is valid
when
values are
equal

121
Digital Signatures – An example: Outlook
To digitally sign all messages:
1. Click on the File tab
Microsoft Support (n.d.). Secure messages by using a digital signature, https://support.office.com/en-us/article/secure-messages-by-
using-a-digital-signature-549ca2f1-a68f-4366-85fa-b3f4b5856fc6, last accessed Dec 24, 2018.

122
2. On the File tab, click Options >Trust Center.

123
3. Then on Trust Center:

124
4. Under rust Center, click Trust Center Settings.

125
5. On the Email Security tab, under Encrypted Mail, select
the Add digital signature to outgoing messages check box.

126
If the calculation takes more than 10mn, the miner will have to
drop this block and move to the next one.
Again, to do this more and more efficiently, more and more
powerful hardware has to be used.
Bitcoin Mining (n.d.). Bitcoin Knowledge Podcast, Bitcoin Mining, Hesiod Services LLC, https://www.bitcoinmining.com/, last
Hiếu, L. Th. (May 13, 2017). Bitcoin Transaction - Double-Spending Attack (51% Attack),
https://www.youtube.com/watch?v=9U2MWaHG-xM, last accessed Aug 21, 2017.
Lead Blockchain Editor (September 12, 2016). Why Investors Should Care About Bitcoin Mining Pools, Bitcoin Investment News,
https://bitcoinira.com/articles/investors-care-bitcoin-mining-pools, last accessed Nov 26, 2017.
To avoid that miners with modest computing power wait more
time to earn BTC rewards, pools were formed to group miners
and distribute BTC rewards on a fairer basis.
To avoid that miners with modest computing power wait more
time to earn BTC rewards, pools were formed to group miners
and distribute BTC rewards on a fairer basis.
The Bitcoin network, for example, is producing 500
petaflops (quadrillion) hashes per second!

127
A mining farm is a site for the production of crypto currency.
A farm is also a collection of powerful computers that miners need.
Mining farms
See http://www.sciencedebate2008.com/fermy-dlya-mayninga-kriptovalyut-eto-uzhe-realnost/, last accessed Nov 26, 2017.

128Wan, T. and Hoblitzell, M. (June 26, 2014). Bitcoin - Fact. Fiction. Future, https://dupress.deloitte.com/dup-us-en/topics/emerging-
Answer (cont’d):
the right value.
Answer (cont’d):
the right value.
6. The miner gets a reward valued in BTC.

129Wan, T. and Hoblitzell, M. (June 26, 2014). Bitcoin - Fact. Fiction. Future, https://dupress.deloitte.com/dup-us-en/topics/emerging-
Answer (cont’d):
the right value.
6. The miner gets a reward valued in BTC.
The reward is then registered in the
blockchain as if it was a transaction.

130
The reward has not always been 50 BTC, and will not always be
50 BTC:
Jan 2009: 50 BTC per mined block.
3Blue1Brown (Jul 7, 2017). Ever wonder how Bitcoin (and other cryptocurrencies) actually work?,
The miner’s reward

25 BTC:
Nov 2012: 25 BTC per mined block.
July 2016: 12.5 BTC
Feb 2020: 6.25 BTC
Sep 2023: etc.
The reward gets cut in half every 210.000 blocks (every 4 years or
so).
25 BTC:
July 2016: 12.5 BTC
Feb 2020: 6.25 BTC
Sep 2023: etc.
so).
Note: This means that there will never be more than 21.000.000
bitcoins in existence:
210,000 (50+25+12,5+6,25….) < 21.000.000.

132
25 BTC:
July 2016: 12.5 BTC
Feb 2020: 6.25 BTC
Sep 2023: etc.
so).
Note: This means that there will never be more than 21.000.000
bitcoins in existence:
210,000 (50+25+12,5+6,25….) < 21.000.000.
210 000,00 x 50,00 = 10 500 000,000210 000,00 x 50,00 = 10 500 000,000
210 000,00 x 25,00 = 5 250 000,000
210 000,00 x 50,00 = 10 500 000,000
210 000,00 x 25,00 = 5 250 000,000
210 000,00 x 12,50 = 2 625 000,000
210 000,00 x 6,25 = 1 312 500,000
210 000,00 x 3,13 = 656 250,000
210 000,00 x 1,56 = 328 125,000
210 000,00 x 0,78 = 164 062,500
210 000,00 x 0,39 = 82 031,250
210 000,00 x 0,20 = 41 015,730
210 000,00 x 0,10 = 20 507,760
210 000,00 x 0,05 = 10 253,880
210 000,00 x 0,02 = 5 126,940
210 000,00 x 0,01 = 2 563,470
210 000,00 x 0,01 = 1 281,840
210 000,00 x 0,00 = 640,920
210 000,00 x 0,00 = 320,460
210 000,00 x 0,00 = 160,230
210 000,00 x 0,00 = 80,010
210 000,00 x 0,00 = 40,110
210 000,00 x 0,00 = 20,034
210 000,00 x 50,00 = 10 500 000,000
210 000,00 x 25,00 = 5 250 000,000
210 000,00 x 12,50 = 2 625 000,000
210 000,00 x 6,25 = 1 312 500,000
210 000,00 x 3,13 = 656 250,000
210 000,00 x 1,56 = 328 125,000
210 000,00 x 0,78 = 164 062,500
210 000,00 x 0,39 = 82 031,250
210 000,00 x 0,20 = 41 015,730
210 000,00 x 0,10 = 20 507,760
210 000,00 x 0,05 = 10 253,880
210 000,00 x 0,02 = 5 126,940
210 000,00 x 0,01 = 2 563,470
210 000,00 x 0,01 = 1 281,840
210 000,00 x 0,00 = 640,920
210 000,00 x 0,00 = 320,460
210 000,00 x 0,00 = 160,230
210 000,00 x 0,00 = 80,010
210 000,00 x 0,00 = 40,110
210 000,00 x 0,00 = 20,034
20 999 980,134

133
The last Bitcoin will be
mined somewhere
between May 7th and
October 8th, 2140.
Bitcoins created
Reward halved every 4 years

134
Where does the 50 BTC come from when mining?
The first 50 BTC come from devaluing all the following bitcoin
rewards by a tiny amount.
Which explains why the reward decreases with time. When all
bitcoins have been exhausted, they disappear.

135
In PoW, validating transactions requires significant resources:
hardware, electricity, time, data storage, bandwidth, …
Source: https://www.blockchain.com/fr/charts/n-transactions?timespan=1year, July 23, 2018.
Validating transactions
In July 2018, Bitcoin reached 182,000 transactions per day.

137
In the beginning, miners solved these math
problems with ordinary processors.
Then they realized that graphics cards used for
gaming were better suited to this kind of working:
Graphics cards (GPUs) are faster
Validating transactions - GPUs

138

139
Hong, E. (Oct 17, 2017). Read more: How Does Bitcoin Mining Work? Investopedia, https://www.investopedia.com/tech/how-does-
bitcoin-mining-work/, last accessed Feb 17, 2018.
Here, the graphics cards are the rectangular blocks with whirring
circles.
Again, this is probably no longer the most efficient way to mine.

140
2300
transistors
In 2017, the largest transistor count in a traditional commercially
available single-chip processor was 19.2 billion: AMD’s Ryzen-
based Epyc.
Moore’s Law

141
Graphics cards (GPUs) are faster
Graphics cards (GPUs) are faster, but they use
more electricity and generate a lot of heat.

142
The first commercial Bitcoin mining chips that
were reprogrammed for mining Bitcoin were
faster but still power-hungry.
ASIC, or Application Specific Integrated Circuit,
for example, are chips that are designed
specifically for Bitcoin mining.
Validating transactions - ASICs

143Bitcoin Mining (n.d.). Bitcoin Knowledge Podcast, Bitcoin Mining, Hesiod Services LLC, https://www.bitcoinmining.com/, last
4.73 Tera Hashes
per second

144Bitcoin Mining (n.d.). Bitcoin Knowledge Podcast, Bitcoin Mining, Hesiod Services LLC, https://www.bitcoinmining.com/, last
4.73 Tera Hashes
per second
1 Tera = 240

145
Martin, W. (16 Oct 2017). The electricity required for a single Bitcoin trade could power a house for a whole month,
https://www.weforum.org/agenda/2017/10/the-electricity-required-for-a-single-bitcoin-trade-could-power-a-house-for-a-whole-month,
last accessed Dec 15, 2017.
0:5
6

146
World’s average electricity price is 18.8 cents per 1 kWh.
Overall, prices vary between 3 cents per kWh in Algeria to 62
cents per kWh in South Korea.
Nail, M. and Di Giuda, M.(Dec 20, 2017). What countries are most profitable for mining?
https://bitnewstoday.com/market/mining/what-countries-are-most-profitable-for-mining/, last accessed Feb 16, 2018.

147
Williams-Grut, O. (Nov. 26, 2017). The electricity used to mine bitcoin this year is bigger than the annual usage of 159 countries,
http://uk.businessinsider.com/bitcoin-mining-electricity-usage-2017-11, last accessed Feb 16, 2018.
The electricity used to mine bitcoin in 2017 was bigger than the
annual usage of 159 countries, including most African countries
This map shows
which countries
consume less
electricity than the
amount consumed
by global bitcoin
mining.

153

154

155

156

157

158

159

160

161

162

163
If you want to estimate how much Bitcoin you could mine with
your mining rig’s hash rate, the site Cryptocompare offers a
helpful calculator.
Hong, E. (Oct 17, 2017). Read more: How Does Bitcoin Mining Work? Investopedia, https://www.investopedia.com/tech/how-does-
bitcoin-mining-work/, last accessed Feb 17, 2018.

165
Fakhri, I. (2016). 5 minutes pour comprendre votre facture de la STEG (Tarifs et paliers), http://efigure.net/les-tarifs-et-les-paliers-de-
facturation-de-lelectricite-et-du-gaz-de-la-steg/, last accessed Feb 17, 2018.

166
Summary
New transactions are broadcast to all nodes.
Each node in the network collects new transactions into a
block.
Miners verify that transactions within each block are legitimate
Each node works on finding a proof-of-work for its block.
When a node finds a proof-of-work, it broadcasts the block to all
nodes.
Nodes validate the block with all its transactions and accept it.
Nodes work on creating the following block in the chain by
using the hash of the just accepted block.
A reward is given to the first miner who solves each blocks
problem/
Verified transactions are stored in the public blockchain.
Somewhat inspired from GitHub (n.d.). Consensus achieved using Proof-of-Work,
https://mastanbtc.github.io/blockchainnotes/consensustypes/, last accessed Mar 3. Also see See Proof of Work vs Proof of Stake:

167See https://www.blockchain.com/fr/pools, July 22, 2018.
The biggest mining pools in July 2018
80% as of June 30, 2018

168
Excerpted from Motherboard (Feb 6, 2015). Life Inside a Secret Chinese Bitcoin Mine,
https://www.youtube.com/watch?v=K8kua5B5K3I, last accessed Apr 6, 2019.
1:4
3

169See https://www.blockchain.com/fr/pools, July 22, 2018.
80% as of June 30, 2018

170
A 51% attack is an infringement to a blockchain which is
performed by a group of miners when they happen to control more
than 50% of the network’s computing power.
These miners will thus be able to prevent new transactions from
gaining confirmations.
While they are in control of the network, they will also be able to
take control of the blockchain to reverse transactions, with the
unwanted consequences (double spend).
Frankenfield, J. (Feb 7, 2019). 51% Attack, https://www.investopedia.com/terms/1/51-attack.asp, last accessed Apr 2, 2019.
51% attacks and double spending
issues

171
accessed Aug 21, 2017 [10:10].
1:0
0
issues

172
Existing blockchain
Ali’s new block
Time
Multiple miners can
create blocks at the same
time, some blocks may be
different.

173
Existing blockchain
Time
Unconfirmed transactions
Multiple miners can
different.
Ali’s new block
Alia’s new block
Multiple miners can
different.
Whose block is going to
be validated first, Ali’s or
Alia’s?

174
Question:
Why does this happen ?
Question:
Answer
Because of network delays (latency)
Question:
Answer
Because of network delays (latency), which are caused by :
issues
Question:
Answer
Processing delays
Queuing delays
Transmission delays
Propagation delays

175
Question:
Answer
Processing delays: the time taken by routers to process packet headers
Queuing delays: the time that packets spend in routing queues
Transmission delays: the time it takes to push the packet’s bits onto the
link
Propagation delays: the time for a signal to reach its destination
issues

176
Existing blockchain
Time
Ali’s new block
Alia’s new block
Multiple miners can create
blocks at the same time,
some blocks may be different.
Whose block is going to be
validated first, Ali’s or Alia’s?
Answer: the one whose nonce
is found first.

177
Existing blockchain
Time
Confirmed transactions
Ali’s block
Multiple miners can create
blocks at the same time,
some blocks may be different.
Whose block is going to be
validated first, Ali’s or Alia’s?
Answer: the one whose nonce
is found first.

178
Existing blockchain
Time
issues

179
Existing blockchain
Time
In case of ties, the new block will always build on the longest
branch.
issues

180
Existing blockchain
Time
Current blockchain
branch.
issues

181Time
Current blockchain
That is exactly what a 51% attack allows to do!
When a miner (or pool of miners) cumulate 51% of the network
worth of computing power, they can insert a fraudulent transaction,
insert the corresponding block in a branch, and make it so that
that branch becomes the longest branch.
branch.
issues

182Time
Final blockchain
More secure Less secure
That is why it is recommended to wait several blocks before considering
received money final.
This ambiguity opens the door to double spend attacks…
issues

183
3blue1brown! (July 11, 2017). Ever wonder how Bitcoin (and other cryptocurrencies) actually work?
https://www.3blue1brown.com/videos/2017/7/11/ever-wonder-how-bitcoin-and-other-cryptocurrencies-actually-work, last accessed
Aug 28, 2017 `[@21:38].
issues

184
51% attackers
cannot create false transactions for someone else unless the
attacker somehow gets access to that person’s unique digital
signature
they can reverse their own transactions and prevent the
confirmation of new transactions.
Therefore, a 51% attack does really not allow to steal someone’s
cryptocurrency. However, it can allow to falsely send
cryptocurrency to someone else, then reverse that transaction and
end up keeping the funds.
Klein, J. (Jan 8, 2019). What is a 51% attack? https://breakermag.com/what-is-a-51-attack/, last accessed Apr 2, 2019.
51% attackers
cannot create false transactions for someone else unless the
attacker somehow gets access to that person’s unique digital
signature.
they can reverse their own transactions and prevent the
confirmation of new transactions.
Therefore, a 51% attack does really not allow to steal someone’s
cryptocurrency. However, it can allow to falsely send
cryptocurrency to someone else, then reverse that transaction and
end up keeping the funds.
Also, the bigger the network, the more difficult a 51%
attack!
issues

185
Issues with the PoW scheme include:
The more difficult the problem, the longer it takes to solve it.
1. GitHub (2018). Proof of Stake FAQ, https://github.com/ethereum/wiki/wiki/Proof-of-Stake-FAQ, last accessed Jan 15, 2018.
Mamoria, M. (Jul 5, 2017). Is Proof of Stake really the solution? https://hackernoon.com/is-proof-of-stake-really-the-solution-
2db68487f4ba, last accessed Jan 14, 2018.
PoW vs. PoS
The more difficult the problem, the more electricity it takes to
compute.
The more difficult the problem, the more electricity it takes to
compute.
Thus, the value of PoW-based cryptocurrencies costs time and
money.
For instance, it is believed that both Bitcoin and Ethereum burn
over $1 million worth of electricity and hardware costs per day1.

186
As a consequence:
With time, miners may ask for higher transaction fees to offset
the diminishing block reward. This will cause the transactions
on the network to be more costly compared to alternatives,
causing more network participants to leave.
If there is a reduction in the number of miners, the mining pool
will become more centralized, increasing the likelihood of 51%
attacks. This could potentially destabilize the network and
cause participants to lose trust in the blockchain.
PoW vs. PoS

187
The proof-of-stake (PoS) scheme is one of the alternatives to the
(PoW).
PoW vs. PoS
In the PoS scheme, the creator of a new block is chosen
depending on its wealth (the stake).
Greenfield, R. (Jul 20, 2017). Explaining How Proof of Stake, Proof of Work, Hashing and Blockchain Work Together,
https://medium.com/@robertgreenfieldiv/explaining-proof-of-stake-f1eae6feb26f, last accessed Jan 14, 2018.
This means that the more coins are owned by a validator, the
more validating power it has.

188
Excerpted from Cryptonauts (Jul 3, 2017). Proof of Work VS Proof of Stake - Simplified Explanation,
https://www.youtube.com/watch?v=SiKnWBPkQ4I, last accessed Jan 14, 2018 @4:30.
0:4
4
PoW vs. PoS

189
The proof-of-stake (PoS) scheme is one of the alternatives to the
(PoW).
PoW vs. PoS
Greenfield, R. (Jul 20, 2017). Explaining How Proof of Stake, Proof of Work, Hashing and Blockchain Work Together,
https://medium.com/@robertgreenfieldiv/explaining-proof-of-stake-f1eae6feb26f, last accessed Jan 14, 2018.
more validating (mining) power it has.
more validating (mining) power it has.
Note:
In the PoS scheme, blocks are “forged” or “minted”, not
mined.
Users who validate transactions and create new blocks in
this system are referred to as “forgers” or “validators”, not
miners.

190
The first cryptocurrency to adopt the PoS scheme was
Peercoin.
Investopedia (n.d.). Proof of Stake (PoS), https://www.investopedia.com/terms/p/proof-stake-pos.asp, last accessed Jan 14, 2018.
Ray, S. (Oct 6, 2017). What is Proof of Stake? https://hackernoon.com/what-is-proof-of-stake-8e0433018256, last accessed Jan 14,
2018.
PoW vs. PoS
The first cryptocurrency to adopt the PoS scheme was
Peercoin.
It was then followed by
Blackcoin
ShadowCash
Lisk
Nxt
and Ethereum.

191
Wikipedia (Apr 8, 2019). Legality of bitcoin by country or territory,
https://en.wikipedia.org/wiki/Legality_of_bitcoin_by_country_or_territory, last accessed Apr 28, 2019.
Cryptocurrencies and the law

192
The difference between Blockchain and
Bitcoin
Network Internet
Blockchain Bitcoin
IBMBlockchain (May 8, 2017). What is the difference between Bitcoin and blockchain, https://www.youtube.com/watch?v=MKwa-
BqnJDg, last accessed Aug 20, 2017.

193
Network Internet
Blockchain Bitcoin
0:1IBMBlockchain (May 8, 2017). What is the difference between Bitcoin and blockchain, https://www.youtube.com/watch?v=MKwa-
BqnJDg, last accessed Aug 20, 2017.
The difference between Blockchain and
Bitcoin

194
How do we know that quality logo is legit?
Application: Food Safety and Provenance

195
A similar example was given by Richie Etwaru using tangerines. See Etwaru, R. (May 15, 2017). Blockchain: Massively Simplified,
TEDxMorristown, https://www.youtube.com/watch?v=k53LUZxUF50, last accessed Aug 21, 2017.
1. Quick Respone Code

196
The same example was given by Richie Etwaru using tangerines. See Etwaru, R. (May 15, 2017). Blockchain: Massively Simplified,
1. Quick Response Code
Imagine that the fig seller puts a QR code1 on the merchandise.

197
We can scan that code with our smartphone.
The same example was given by Richie Etwaru using tangerines. See Etwaru, R. (May 15, 2017). Blockchain: Massively Simplified,
1. Quick Response Code
An app opens showing all the transactions that took place on
that merchandise including all the chemicals that were applied
in the farm where it came from.
An app opens showing all the transactions that took place on
that merchandise including all the chemicals that were applied
in the farm where it came from.
And it is all running on a blockchain so that we know that we
can trust it.

198Excerpted from LibertyPen (August 26, 2008). Power of the Market - The Pencil, https://www.youtube.com/watch?v=R5Gppi-O3a8, last accessed J
1:09

199
The spinach outbreak in 2006
which caused national wide
kidney failures.
Consequently, all spinach was
recalled nationwide.
IBM Watson Internet of Things (Feb 16, 2017). Genius of Things: Blockchain and Food Safety with IBM and Walmart,
https://www.youtube.com/watch?v=MMOF0G_2H0A, last accessed Mar 30, 2018 @5:40.
Food safety

200
It took two weeks to trace it
back to the original farm.
When it was done, they found
out it was one supplier, one
farm, one lot, one day.
Food safety

201
It took two weeks to trace it
back to the original farm.
When it was done, they
found out it was one
supplier, one farm, one lot,
one day.
Food safety

202
Raw Material
Suppliers
End Customers
Distribution
Warehouses
Manufacturing
Plants
Retailers

203
Raw Material
Suppliers
End Customers
Distribution
Warehouses
Manufacturing
Plants
Retailers

204
At each transaction, a new block
is generated and added to the
Blockchain.
Each time, all parties validate the
transaction.

205
Partz, H. (Mar 2, 2018). Walmart To Implement Blockchain-Based Delivery System, https://cointelegraph.com/news/walmart-to-implement-blockch
28, 2018.
From grower to grocer.
From farm to fork.
From grass to glass.

206
Walmart, the world largest retailer a company that serves 240
million customers every week.

207
Thus, this technology could be used for tracking fresh food from
the grower to grocer (reducing waste and costs).
This implies documenting inspections, and recording the chain
of custody through time-stamped blockchain transactions.
Stanley, J. (Feb 5, 2018). Blockchain Explained: How It Works, Who Cares and What Its Future May Hold - Is Blockchain the Swiss
Army Knife to All of Our Cyber-Insecurities?, TechSpot, https://www.techspot.com/article/1567-blockchain-explained/, last accessed
Feb 17, 2018.
Food safety

208
Other Use Cases: Land Titles

209
In Ghana around 78% of land
is unregistered.
A lot of land dispute problems.
Corruption and nepotism have
plagued every area of the
public sector.
Aitken, R. (Apr 5, 2016). Bitland's African Blockchain Initiative Putting Land On The Ledger, https://www.forbes.com/sites/rogeraitken/20
initiative-putting-land-on-the-ledger/#1a87344e7537, last accessed Jan 25, 2018.
Bitland, based in
Bloomington, Indiana, aimed
to register land titles to a
public blockchain, so that
ownership is not only public -
but immutable.

210
Haiti, when the earthquake happened—most, if not all, of the land
titles were held in one building, which was destroyed.
You have a nation now that doesn’t have land titling.
McKinsey (May 2017). What next for blockchain? https://www.mckinsey.com/industries/high-tech/our-insights/what-next-for-
blockchain, last accessed Mar 25, 2018.
30% of the titles in the
US have errors in them.

211
See http://edition.cnn.com/SPECIALS/2001/trade.center/tenants1.html
Glatersept, J.D. (Sept 13, 2001). After the Attacks: the Records; Corporate Paper Trails Lie Buried in Soot,
https://www.nytimes.com/2001/09/13/business/after-the-attacks-the-records-corporate-paper-trails-lie-buried-in-soot.html, last

212
The SEC (Security and Exchange
Commission) will have to reconstruct
much of its work regarding
investigations and litigation,
according to Carmen Lawrence, who
headed the New York operations
from 1995 to 2000.
The files were largely in paper form,
and the SEC had to reconstruct
them.
Glatersept, J.D. (Sept 13, 2001). After the Attacks: the Records; Corporate Paper Trails Lie Buried in Soot,
https://www.nytimes.com/2001/09/13/business/after-the-attacks-the-records-corporate-paper-trails-lie-buried-in-soot.html, last
accessed Apr 1, 2018.

213
Other Use Cases: Property
Management

214
Management

215
Management

216
Management

217
Management

218
T
T
H
H
A
A
N
N
K
K
S
SSong: Extracted from the song 141120 TK music sn04.-27510, by Artist: Pleasure Park Music - Licensed by AdRev for Rights Holder
(on behalf of Pleasure Park Music), https://soundcloud.com/zoxfox87/141120-tk-music-sn05-1, last accessed July 27, 2018.

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