Limitations of Blockchain.docx

Limitations of Blockchain
Complexity of Blockchain
Even though Blockchain technology has made cryptography
mainstream, this highly specialized industry is still full of
technical jargon. However, there were several successful efforts
made to provide glossaries and indexes so we would understand
it more accessible.
The 51% Attack
With the growing number of nodes or blocks in a blockchain

technology, the vulnerabilities associated with the entire
blockchain also increases. Among all the possible security flaws
that can affect the blockchain network, there is one unavoidable
security flaw.
51% attacks are among the most discussed. Such an attack may
happen if one entity manages to control more than 50% of the
network hashing power, which would eventually allow them to
disrupt the network by intentionally excluding or modifying the
ordering of transactions.
High Energy Consumption
In the case of Bitcoin blockchain, energy consumption remains
one of the biggest issues with miners. Researchers at the
University of Cambridge have estimated that Bitcoin consumes
more energy than the entire nation of Switzerland. The energy is
mainly fed to keep the entire network alive all the time. That’s
just one blockchain, imagine the case if we have many more
such networks.
Scalability
Blockchains, especially those using Proof of Work, are highly
inefficient. Since mining is highly competitive and there is just
one winner every ten minutes, the work of every other miner is
wasted. As miners are continually trying to increase their
computational power, so they have a greater chance of finding a
valid block hash, the resources used by the Bitcoin network has

increased significantly in the last few years.
Bitcoin works on Proof-of-Work model which is secure but slow
at the same time. There is an alternative in the form of Proof-of-
Stake, which is faster in validating entries, but is not regarded
as an ideal option for distributed consensus protocol.
Lack of Skilled Technicians
There is always a risk of error occurring, if the human factor is
involved. In case a blockchain serves as a database, all the
incoming data must be of high quality. If all occurring events
are not originally registered with accuracy, then the
trustworthiness of the stored data could be seriously in doubt.
In case unreliable, incorrect information goes into the
blockchain, then unreliable, incorrect data will also go out from
it.
Lack of Distributed Execution
Under partitioning, a distributed data system can either be
consistent or available but not both at the same time.
Blockchain gives up on consistency to be available and partition
tolerant.

Viability and Sustainability
The strategic value of blockchain will only be realized if
commercially viable solutions can be deployed at scale. The
relative immaturity of blockchain technology is a limitation to
its current viability. The misconception that blockchain is not
viable at scale due to its energy consumption and transaction
speed is a conflation of Bitcoin with blockchain.
The technical configurations are a series of design choices in
which the levers on speed (size of block), security (consensus
protocol), and storage (number of notaries) can be selected to
make most use cases commercially viable.
Faster block-times
A consequence of fast block-time is reduced security, therefore
many blockchain applications require confirmation for newly
mined blocks to secure the transactions from double-spending.
Additional Challenges
Environmental Cost
Lack of Regulation
Slow and Cumbersome
“Establishment”
Risk of Error
Blockchain Bloat

Data Modification
Private Keys
Strategic Value
Common Standards
Advancement of Tech
Digitalized Assets
Network Growth
Political Aspect
Storage
© Translational lung cancer research. All rights reserved. Transl
Lung Cancer Res 2014;3(5):280-285www.tlcr.org
In the 20th century, tobacco smoking was the leading
health burden and the major cause of death in the world.
It is estimated that around 100 million people died from
smoking-attributed diseases at that time (1). The epidemic of
cigarette smoking in the past century was mostly continued
in developed countries. Recent estimates show that
currently 1.2 billion people use tobacco worldwide, mostly
in developing countries. Based on current trends in tobacco
exposure, 8 million people will die every year by 2030 from
different forms of tobacco (2). Since the 1960s, smoking
rates and its health consequences have gradually decreased
in rich countries and have rapidly increased in developing
countries, including the region of Central and Eastern
Europe (3). Poland, being at the time part of the communist
bloc, was among countries with particularly high tobacco
consumption. In the mid-1970s and early 1980s, 65% to
75% of Polish men aged 20 to 60 smoked cigarettes every
day (4). In consequence, Poland faced a catastrophically high
level of premature mortality among young and middle-aged
adults. By 1990, over 40% of Polish men died prematurely

from smoking-attributed diseases (5). The health impact
of smoking, including cancer, was particularly high in poor
and uneducated groups of society (6). At that time, effective
tobacco-control measures, such as increasing taxes on
tobacco products, ban on tobacco advertising and promotion,
health warnings on tobacco products and advertisements, as
well as establishing “non-smoking” areas, were already well
known in Europe and worldwide. However, Poland was one
of the largest tobacco producers in Europe, and this state-
run industry was a source of high revenues (7). Hence, in
view of the difficult economic situation of the country, the
government did not undertake any real tobacco-control
legislative measures, and sparse tobacco-control regulations
were ineffective because of a lack of their enforcement.
After the fall of the communist system [1989-1990] and
the introduction of a market economy, the tobacco industry
in Poland was extensively privatized and in over 90% of
cases became the property of multinational corporations. In
view of the dramatic decline in the prevalence of smoking in
North America, Poland, along with other Eastern European
countries, became a fertile field for future growth and a
strategic target of the international tobacco companies. In
1990, it was planned to increase cigarette sale in Poland by
10-20% by 2000 (8). In the first half of 1990, new attractive
Review Article
Tobacco control in Poland—successes and challenges
Jacek Jassem1, Krzysztof Przewoźniak2, Witold Zatoński2
1Department of Oncology and Radiotherapy, Medical University
of Gdańsk, Gdańsk, Poland; 2Department of Cancer
Epidemiology and Prevention,

Maria Skłodowska-Curie Cancer Center and Institute of
Oncology, Warsaw, Poland
Correspondence to: Jacek Jassem, MD, PhD. Department of
Oncology and Radiotherapy, Medical University of Gdańsk, 7
Dębinki St., 80-211 Gdańsk,
Poland. Email [email protected]
Abstract: For many years, tobacco smoking was the major single
avoidable cause of premature mortality
in Poland. In the 1970s and 1980s, Poland was a country with an
extremely high prevalence of smoking and
lung cancer mortality among men in the world. By 1990, over
40% of Polish men died prematurely from
smoking-attributed diseases. However, the enforcement of
comprehensive tobacco-control measures and
programs based on the World Health Organization
recommendations and the best practices from other
countries, contributed to a spectacular decrease of smoking
incidence, particularly in men. This led to
dramatic decrease in lung cancer incidence and mortality, and to
a substantial improvement in public health
in Poland. This article reviews the achievements of tobacco-
control in Poland over the past decades and
points out current challenges in this field.
Keywords: Tobacco control; Poland; successes and challenges
Submitted Sep 12, 2014. Accepted for publication Sep 28, 2014.
doi: 10.3978/j.issn.2218-6751.2014.09.12
View this article at: http://dx.doi.org/10.3978/j.issn.2218-
6751.2014.09.12

281Translational lung cancer research, Vol 3, No 5 October
2014
cigarette brands became easily available and were relatively
cheap due to government concessions to multinational
companies by keeping tobacco taxes low for several years.
Tobacco companies introduced aggressive advertising of
their products in the private media, especially on billboards
and in the press (television advertising was already banned at
that time). In consequence, smoking rates increased steadily,
particularly among children and adolescents. According to
data of the World Health Organization (WHO) and the
Polish Central Statistical Office, Poland reached an average
cigarette consumption of over 3,600 cigarettes per adult
person per year, thus zooming from 11th place in 1972 to
the first in the world in 1992 (9). Heavy smoking was taking
a deadly toll in high rates of lung cancer and cardiovascular
diseases. The estimated number of deaths in Poland caused
by tobacco smoking in 2000 reached approximately 69,000,
of which 43,000 occurred prematurely i.e., between the ages
of 35-69 (5). Around 43% of all deaths in males aged 35-
69 were caused by smoking; middle aged adult smokers lost
nearly 22 years of life and smokers aged 70 and older lost an
average of 8 years of life (5). Lung cancer killed half of all
Polish men who died before reaching 65 (6).
Fortunately, democratic changes in the 1980s resulted
in a more open society and a movement towards the rapid
development of civil society. This led to the creation of
health-focused non-government organizations (NGOs),
such as the Health Promotion Foundation and the Polish
Anti-Tobacco Society, which emphasized the devastating
effects of smoking and the need for comprehensive tobacco-

control legislation. These organizations, supported by
health professionals, the free media, and local communities,
were very instrumental in large-scale counter-tobacco
promotion and educational activities. Examples of such
nationwide actions included an annual campaign entitled
“Let’s Stop Smoking Together” that has been based on the
Great American Smoke-Out and aimed at convincing as
many smokers as possible to make a serious attempt to quit
smoking. This population-based smoking cessation program
included social and media campaigns, professional and
community-based support for smokers, and a competition
that motivated smokers to quit smoking and, as an award,
to take part in a one-week trip to Rome, including a private
audience with Pope John Paul II (8,10). Between 1992 and
2006, almost half a million Polish smokers took part in the
contest. Nation-wide surveys estimated that over 4 million
smokers decided to give up smoking between 1992 to 2008
as a result of the Great Smoke-Out campaign (11).
Medical doctors and health institutes were particularly
active in building capacity for tobacco-control in Poland.
The first smoking cessation clinics were established in
the 1980s. The Polish Quitline, that was based on the
best practices taken from the UK Quit® and Norwegian
Quitline, was established in 1996 and was first in Central
and Eastern Europe. In 2002, the Supreme Medical
Council announced the “Declaration on Counteracting
Nicotine Dependence” calling for the intensification of
tobacco-control activities in the Polish medical community
by creating health-conscious attitudes and rising health
awareness in society (12). A few years later, several medical
associations signed the Consensus on the Diagnostics and
Treatment of Tobacco Dependence—a key guideline on
smoking cessation addressed to all health professionals in
Poland (13). In the meantime, separate guidelines have been

published by general practitioners, cardiologists, oncologists
and chest physicians, and over 10,000 physicians and nurses
have been trained in methods of smoking cessation. Polish
medical and scientific societies in cooperation with the
WHO, the International Union Against Cancer (UICC),
the American Cancer Society (ACS) and other international
organizations and institutions launched several scientific
studies on tobacco control in Poland and organized a series
of large workshops and scientific conferences on tobacco
and health. All these activities raised public awareness of
tobacco-related dangers and proved to be truly effective.
It has been estimated that the number of daily smokers
diminished from 14 million in 1982 to 9 million in 2010 (11).
The most successful tobacco-control activity undertaken
in the past 25 years in Poland, however, was the enforcement
of comprehensive legislative measures in this field (8). In
November 1990, very soon after democracy came to Poland,
a working group at the Institute of Oncology in Warsaw
invited the WHO, UICC, ACS, public health leaders and
tobacco-control advocates from Western and Eastern Europe
to Kazimierz in Poland in order to discuss and prepare a
long-term strategy for “A New Tobacco Free Europe”. The
Kazimierz Declaration was a milestone for the enforcement
of tobacco-control legislation in Central and Eastern
Europe including Poland, and one of the few public health
resolutions that have been fully implemented. A few years
later, the same group of Polish tobacco-control advocates
developed policy recommendations and prepared a draft of a
tobacco control bill in Poland. The bill, based on the WHO
gold standard, included a comprehensive set of provisions
for reducing the tobacco epidemic in Poland. This initiative
faced a furious counteraction from the powerful and well
organized tobacco lobbies, who questioned the impact of

282 Jassem et al. Tobacco control in Poland
an advertising ban, health warnings, economic regulations
and public health education. They also emphasized the
right to free advertising and the potential adverse impact
on the Polish economy. Meanwhile, however, Polish public
attitudes on this matter have turned to smoke-free solutions,
and political parties took notice. The members of the
Sejm (the lower house of the Polish Parliament), including
around 40 medical doctors, were encouraged to vote for
the Tobacco-Control Bill. As a result, in November 1995,
the Polish Parliament with an overwhelming majority from
all political parties, passed new tobacco-control legislation,
the toughest in any of the former communist countries
of Eastern Europe. Its main provisions and subsequent
amendments in 1999 and 2002 included:
• A ban on smoking and the sale of cigarettes in health
care centers, schools and enclosed workplaces;
• A ban on the sale of tobacco to minors (under 18) and
by vending machines;
• A ban on electronic media advertising, including radio
and television (in 1999 extended to all media);
• A ban of tobacco promotion and sponsorship;
• 30% textual health warnings on cigarette packs (one
of the largest in the world at that time);
• Free provision of treatment for smoking dependence;
• The gradual reduction of tar, nicotine and carbon

monoxide according to the European Union (EU)
standards;
• Developing the government program aimed at
reducing health and socio-economic consequences of
smoking in Poland;
• Establishing a tobacco-control fund comprising of a levy of
0.5% from the excise tobacco tax for the abovementioned
program (however, actual funds transferred annually for
tobacco-control were substantially lower).
Furious attempts by the tobacco lobby to block the new
legislation, in particular to thwart the introduction of the ban
on tobacco advertising and promotion and the placement
of large health warnings on cigarette packs, failed (8).
These regulations made Poland a country with a most
favorable climate for tobacco-control and a model for other
countries. The WHO welcomed it as “an example for the
rest of the world” (14) and the World Bank praised it as a
“courageous” move (15). This Polish legislation became the
best practice for new members of the EU, and the provision
on large health warnings on cigarette packs were proposed to
be enacted by the European Parliament for all EU countries.
The next challenge for tobacco-control in Poland was
to reduce exposure to tobacco smoke in public places and
worksites. This issue was addressed in the Framework
Convention on Tobacco Control (FCTC) developed in
2003 by WHO and ratified by Poland in 2006 (16). The
FCTC (Poland was one of its initiators) was the first
convention of the United Nations regarding public health.
This document became a guidepost for global, regional, and
national health policies and was ratified by the European

Parliament in 2005. In 2007, the European Commission
developed a strategy for reducing smoking in public places
and workplaces (17) and, in 2009, the European Parliament
issued a respective resolution. By that time, the ban on
smoking in public places had already been introduced in
some EU countries (for example, Ireland and England)
and in Norway. Yet, the road to smoke-free Poland was
again winding. The first draft of the legislation that banned
smoking in public places was developed again by the medical
community and first presented publicly in April 2006. A few
months later, the new legislation was formally submitted
to the Parliament as a project of the Parliamentary Health
Commission. As expected, this sparked a vivid debate
within the country, heated by the tobacco lobby. This
time it was argued that the legislation was too strict and
would limit civic freedom. Tobacco lobbyists and some
parliamentarians warned that the new regulations would
lower revenues from tobacco taxes, and cause bankruptcies
and the scrapping of jobs on a large scale, especially in
hospitality industry. Despite this, a Polish Radio survey
conducted in 2006 showed that 77% of Poles supported the
complete ban on smoking in all public places, and similar
results were obtained in subsequent surveys performed in
2007 and 2008. Finally, after numerous discussions and
modifications, the ban and other tobacco-control measures
were enacted in April 2010 and came into effect six months
later. With that, Poland joined ten other Europeans
countries which enforced by that time a smoke-free policy
in their countries. The new legislation foresaw a smoking
ban in all workplaces, hospitals and other outpatient clinics
and premises for patients, all educational premises, all
means of public transport, bars and restaurants, public
cultural and leisure venues, bus, tram, and train stops and
children’s playgrounds. However, according to the obtained
political compromise, owners of venues in the hospitality
sector, retirement homes, airports and universities might

build (but were not obliged) special tightly sealed and
ventilated smoking rooms. These regulations contributed to
substantial changes in smoking behaviors and exposure to
tobacco smoke in Poland. In a public survey conducted by
the Cancer Center and Institute in Warsaw, in collaboration
2014
with TNS Poland one year after enacting the ban, over
1 million Polish smokers had made a serious attempt to quit
smoking or had quit smoking for good. Results of nation-
wide surveys, conducted by the Chief Sanitary Inspectorate
and TNS Poland in 2009 and 2013, showed that exposure
of smokers to tobacco smoke in workplaces dropped from
41% to 8% and that of non-smokers from 19% to 6%.
Additionally, Poles declared a substantial decline in smoking
tobacco in the presence of children (from 53% to 23%),
pregnant women (25% to 11%) and non-smokers (83% to
54%). Surveys conducted before and after the enforcement
of the ban on smoking in public places and worksites
also showed an increase in public support for smoke-free
policies, especially in bars and restaurants.
Besides the enforcement of smoke-free policies in
Poland, new tobacco-control regulations included a gradual
increase of tobacco excise taxes. Since the beginning of the
1990s, excise tax for cigarettes sold in Poland has increased
over four times and now constitutes around two-thirds of
the weighted average price, following the EU’s excise tax
rules. This led to a substantial increase in tobacco prices

in Poland, especially for manufactured cigarettes (18).
However, cigarette prices are still low when compared
to other EU countries, especially in Western Europe.
Additionally, Poland’s rapidly growing economy has
resulted in higher affordability of tobacco products.. Hence,
increases in excise duties and prices of cigarette and other
tobacco products should be steadily continued.
Lasting for over two decades, legislative and other efforts
to combat tobacco in Poland has paid off. According to the
year books of the Central Statistical Office of Poland, the
number of sold cigarettes in Poland decreased from 101 billion
per year in 1995 to 47 billion in 2013. Between 1980 and 2013,
the proportion of smokers among men dropped from 65%
to 28% and among women from 32% to 18%. If this trend
continues, the consumption of cigarettes per capita in Poland
in 2040 will fall to the level of the 1920s (Figure 1). Changes in
cigarette consumption and smoking behavior have contributed
to a substantial improvement in the health of the Polish
population. According to the National Cancer Register, age-
standardized mortality rates per 100,000 from lung cancer in
men declined from 71.1 in 1990 to 56.2 in 2010. The patterns
of changes in lung cancer mortality among Polish men became
similar to those observed two decades earlier in the Unites
States (Figure 2). Between 1991 and 2005, the death rate from
coronary heart disease halved in Poland, and 15% of this
decrease in men was attributable to reduced smoking (19).
However, considerable progress in tobacco-control in
Poland has been facing challenges. In the years 2003-2012,
tobacco production in Poland increased by 90%, of which
around two-thirds is now exported. This places Poland
third in Europe, after Germany and the Netherlands in
tobacco production and sale. In consequence, Poland ceased
to support EU policy restricting smoking, and does not

implement consecutive FCTC regulations, such as pictorial
health warnings on tobacco packs. Recently, Poland also
appealed against the EU ban on flavored tobacco products.
A worrying phenomenon is the persistently high proportion
of smoking women. In the 35-44 age bracket, there is almost
a gender parity between smokers (34% of women and 32%
of men) (11). Although a similar trend has been reported
elsewhere, Poland is among the countries with a particularly
high prevalence of smoking women (20). In consequence,
whilst the mortality rates from lung cancer among men are
rapidly decreasing, they are still on the rise among women
(Figure 3). The levels of premature mortality of young
and middle-aged adults remain above those in Western
Europe (21). The percentage of smokers is particularly
50
45
40
35
30
25
20
15
10
5
0

2000 2003 2005 2007 2009 2011 2013
P
e
rc
e
n
ta
g
e
(Years)
Males
Females
R
a
ti
o
(Years)1963 1968 1973 1978 1983 1988 1993 1998
2003 2008
Poland
USA
70
60
50
40

30
20
10
0
Figure 1 Percentage of daily smokers in Poland by gender,
2000-
2013. Source: Polish nation-wide survey “Social Diagnosis
2013”.
Figure 2 Standardized lung cancer mortality (ratio/100,000) in
Poland and USA, men aged 35-54, 1963-2010. Source: WHO
health database.
284 Jassem et al. Tobacco control in Poland
high among less educated and unemployed Poles, reaching
even 50% in men. While smoking traditional cigarettes is
decreasing, there is a rise (including children) in the use
of much cheaper, manually rolled cigarettes, water pipes
(shisha) and electronic cigarettes (22,23).
There is certainly still room for improvement in tobacco-
control in Poland (24). The government should consistently
continue a tobacco-control policy according to the FCTC
regulations and the 2012 EU directive (25). In the coming
years, the following tobacco-control measures should be

enforced in Poland:
• Raising awareness of tobacco smoking dangers
through the continuous nationwide education of
children and adolescents, teachers and educators;
• The introduction of large pictorial health warnings on
all tobacco packs and information on the harmfulness
of toxic substances in cigarettes;
• The introduction of plain cigarette packages;
• The placement of the Quitline number on all tobacco
packs;
• A complete ban of tobacco advertisement in points of
sale and in Internet;
• A complete ban of smoking in all public facilities;
• A ban on the sale of aromatic (e.g., menthol) and ‘slim’
cigarettes
• A ban on the sale of smokeless tobacco, including
nasal snuff, electronic cigarettes and herbal smoking
products;
• Stricter regulation for roll-ups prepared from loose
tobacco and smuggled tobacco products.
The recently developed “Strategy for Cancer Control in
Poland 2015-2024” (available at http://www.walkazrakiem.pl/)
includes several long-term intervention measures to reduce
the incidence and impact of recognized cancer risk factors,
including tobacco smoking and passive exposure to tobacco
smoke. This would vastly be facilitated by continued

cooperation in this field between government institutions and
NGOs. Finally, government programs to limit health and
socio-economic consequences of smoking tobacco should
receive adequate financial support. If all abovementioned
tobacco control measures are successfully enforced, Poland
will join again a group of leading countries in tobacco-
control, and substantially improve its indicators in public
health.
Acknowledgements
Disclosure: The authors declare no conflict of interest.
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Cite this article as: Jassem J, Przewoźniak K, Zatoński
W. Tobacco control in Poland—successes and challenges.
Transl Lung Cancer Res 2014;3(5):280-285. doi: 10.3978/
j.issn.2218-6751.2014.09.12
Curbing TobaCCo use in Poland �
O
nly two major causes of death are growing
worldwide: AIDS and tobacco. While the
course of the AIDS epidemic is uncertain, one
can be more sure that current smoking pat-
terns will kill about 1 billion people this century, 10 times
more than the deaths from tobacco in the 20th century.1
Much of this burden will fall on poor countries and the
poorest people living there. While smoking rates have fall-

en in rich countries over the past two decades, smoking is
on the rise in developing countries.2 Currently, more than
three quarters of the world’s 1.2 billion smokers live in
low- and middle-income countries, and smoking-related
deaths are estimated to double in number by 2030.
As Poland’s story shows, there is reason to hope that
concerted efforts to tackle the growing smoking prob-
lem in low- and middle-income countries can succeed.
In many instances, this will likely take a very high level
of political commitment—enough to counter the sig-
nificant economic influence of the tobacco industry—as
well as state-of-the-art communication strategies to
induce major shifts in attitudes toward smoking.
Lighting Up: Dangers of Tobacco
Smoking causes an astonishingly long list of diseases,
leading to premature death in half of all smokers. To-
bacco is implicated in numerous cancers including blad-
der, kidney, larynx, mouth, pancreas, and stomach. Lung
Case 14
Curbing Tobacco Use in Poland
Geographic area: Poland
Health condition: in the �980s, Poland had the highest rate of
smoking in the world. nearly three quarters
of Polish men aged 20 to 60 smoked every day. in �990, the
probability that a �5-year-old boy born in Po-
land would reach his 60th birthday was lower than in most
countries, and middle-aged Polish men had one
of the highest rates of lung cancer in the world.

Global importance of the health condition today: Tobacco is the
second deadliest threat to adult health
in the world and causes � in every �0 adult deaths. it is
estimated that 500 million people alive today
will die prematurely because of tobacco consumption. More
than three quarters of the world’s �.2 billion
smokers live in low- and middle-income countries, where
smoking is on the rise. by 2030, it is estimated
that smoking-related deaths will have doubled, accounting for
the deaths of 6 in �0 people.
Intervention or program: in �995, the Polish parliament passed
groundbreaking tobacco-control legisla-
tion, which included the requirement of the largest health
warnings on cigarette packs in the world, a ban
on smoking in health centers and enclosed workspaces, a ban on
electronic media advertising, and a ban
on tobacco sales to minors. Health education campaigns and the
“great Polish smoke-out” have also
raised awareness about the dangers of smoking and have
encouraged Poles to quit.
Impact: Cigarette consumption dropped �0 percent between
�990 and �998, and the number of smokers
declined from �4 million in the �980s to under �0 million at
the end of the �990s. The reduction in smok-
ing led to �0,000 fewer deaths each year, a 30 percent decline
in lung cancer among men aged 20 to 44,
a nearly 7 percent decline in cardiovascular disease, and a
reduction in low birth weight.
Case drafted by Molly Kinder.
2 Curbing TobaCCo use in Poland

cancer is the most common disease caused by smoking,
and overall, smoking is responsible for about one half of
all cancer deaths.3 Smoking is also a major cause of car-
diovascular diseases, including strokes and heart attacks,
and of respiratory diseases such as emphysema. Addi-
tional health threats are emerging as research advances.
A recent study in India found that smoking accounts for
about half of the country’s tuberculosis deaths and may
well be increasing the spread of infectious tuberculosis.4
Cigarette smoking takes a heavy toll not only on smok-
ers but also on those around them, particularly young
children. Passive smoking (inhaling smoke in the sur-
rounding air) contributes to respiratory illnesses among
children including ear infections, asthma attacks, sinus
infections, and throat inflammations. Tobacco use in
and around pregnant women can contribute to sudden
infant death syndrome, low birth weight, and intrauter-
ine growth retardation.5
Smoking places an economic burden on individuals,
families, and societies chiefly because of its massive
death and disability toll and also because of the high
cost of treatment, the value of lost wages, and the diver-
sion of income from other basic needs such as children’s
food.6 Because the poor are more likely to smoke than
their rich neighbors, the economic and health impact
of smoking disproportionately burdens the poor. In
Poland, most of the gap in risk of dying early between
uneducated and educated men is due to smoking.7
Furthermore, because cigarettes claim the lives of half of
their users, often during their prime years, smoking robs
countries of valuable labor and strains health systems.
Curbing Tobacco Use

Compared with controlling other health scourges,
stopping the deadly effects of smoking requires chang-
ing personal behavior rather than undergoing complex
medical procedures. Preventing smoking-related cancer
and respiratory disease simply requires that smokers
quit smoking and that fewer people light up their first
cigarette. Because most tobacco deaths over the next
few decades will occur among today’s smokers, getting
adults to quit is a special priority.2,8
However, despite the clear health and economic benefits,
quitting is extremely difficult. In addition to having to
combat the addictive nature of nicotine, those seeking
to reduce cigarette consumption are stymied by the fact
that smoking is an ingrained social norm whose popu-
larity is sustained through billions of dollars worth of
cigarette advertising (which in the United States alone
totaled over $11 billion in 2001).9 Moreover, many
smokers in developing countries are unaware of the link
between smoking and health—just as was the case in the
United States and other industrialized countries before
the mid-1960s. In China, for example, a survey discov-
ered that more than half of Chinese smokers and non-
smokers thought that smoking did “little or no harm.”10
Although changing the behavior of smokers is daunt-
ing, it can be done—and it has been done. Governments
and civil society can implement proven and highly
cost-effective interventions to control tobacco use.
Governments have at their disposal a range of legislative
measures that can limit the supply of cigarettes and pro-
mote nonsmoking behavior, including increasing taxes
on tobacco products; limiting tobacco advertising and
promotion; limiting the harmful ingredients in tobacco

products; requiring health warnings on products and
advertisements; and establishing “nonsmoking” ar-
eas.2,8,10 Both the government and civil society can work
to educate the public about the negative health effects of
smoking.
Implementation of such interventions requires high lev-
els of political commitment, as well as the determination
and energy of civil society and antitobacco advocates to
counter commercial interests. Tobacco companies are
well financed and have played a key role in thwarting
progress in tobacco control internationally.11
Poland: Highest Cigarette Consumption
in the World
Before the fall of the Berlin Wall in 1989, Poland had
the highest cigarette consumption in the world. In the
late 1970s, the average Pole smoked more than 3,500
cigarettes each year. Nearly three quarters of Polish men
aged 20 to 60 smoked every day, and by 1982, 30 percent
of adult women smoked regularly.12,13
The impact on the health of Poles was staggering. In
1990, the probability that a 15-year-old boy born in
Poland would reach his 60th birthday was lower than
Curbing TobaCCo use in Poland 3
most countries in the world—even India and China.
Half of these early deaths were attributable to tobacco
consumption.12 Middle-aged Polish men had one of
the highest rates of lung cancer in the world—higher
than every European country except for Hungary—and

other smoking-related illnesses, such as laryngeal and
oral cancer, were at all-time high levels. It is estimated
that 42 percent of cardiovascular deaths and 71 percent
of respiratory disease in middle-aged men were due to
smoking.
Few Poles were quitting, largely because of the politi-
cal and social climate of the time. Because the state-run
tobacco production was a significant source of revenue,
the government—which controlled information—did
not fully disclose the negative consequences of smoking.
As a result, Polish smokers were less informed about
the dangers of smoking than most of their European
neighbors. In addition, tobacco-control laws were rarely
enforced, and stronger tobacco-control legislation intro-
duced in the early 1980s was rejected by the government
because it was seen as a threat to government revenue
during an economic downturn.
The dramatic social, economic, and political changes
ushered into Poland after the fall of communism ini-
tially exacerbated Poland’s addiction to tobacco. When
a market economy replaced the state-run system in
1988 and 1989, the tobacco industry was one of the first
to be privatized—opening the country to the powerful
influence of multinational corporations. In less than a
decade, multinationals had taken over more than 90
percent of Poland’s lucrative tobacco industry. Suddenly,
cigarettes in Poland were available in abundant sup-
ply and in more tempting variety. International brands
flooded the market, along with popular new domestic
brands like Solidarnosc and Lady Di. Adding to their
appeal, cigarettes were also cheap, less than the price of a
loaf of bread—thanks to deals made between the corpo-
rations and the Polish government that kept prices down
during the first half of the 1990s.

At the same time, democratic changes sweeping the
country brought with them a potent force: savvy and
state-of-the-art marketing. Tobacco companies poured
more than $100 million into Poland, making the to-
bacco industry the largest advertiser in the country. The
industry aggressively set out to increase consumption by
10 percent a year. As a result, smoking rates in the early
1990s climbed steadily, particularly among children
aged 11 to 15.12
Roots of the Tobacco-Control
Movement
As the tobacco epidemic was escalating in the early
1990s, historic changes in Poland set in motion powerful
influences that helped amplify antitobacco voices.
Poland’s scientific community laid the foundation of the
antitobacco movement when they first established the
in-country scientific evidence illustrating the devastat-
ing health impact of smoking. Research conducted in
the 1980s by the Marie Sklodowska-Curie Memorial
Cancer Centre and Institute of Oncology contributed
to the first Polish report on the health impact of smok-
ing, highlighting in particular the link between smoking
and the escalating cancer outbreak in Poland. The body
of evidence about the harmful effects of smoking and
the need for tobacco-control legislation were further
strengthened through a series of international work-
shops and scientific conferences held in Poland.
With solid evidence now in hand, Poland’s budding civil
society took up the call for tobacco-control measures.
Health advocates in Poland were first brought together

around the antismoking cause in the 1980s as civil
society was experiencing a renewal. During this time,
antitobacco groups such as the Polish Anti-Tobacco So-
ciety formed and began to interact with the WHO, the
International Union Against Cancer, and other interna-
tional groups.
Later in the new political milieu, when nongovernmen-
tal organizations (NGOs) could freely form, Poland’s
civil society had an even stronger voice. In 1990, Poland
hosted “A Tobacco-Free New Europe” conference of
western and eastern European health advocates, which
resulted in a set of policy recommendations that would
later prove instrumental in shaping Poland’s own anti-
tobacco laws. Finally, the Health Promotion Foundation
was established to lead health promotion and antito-
bacco education efforts.
The free media was essential to the success of the ad-
vocates’ movement to control tobacco use. In the new
democratic era, the Polish press could cover health
issues, including the reporting of scientific studies
illustrating the health consequences of smoking. The
dissemination of this information raised awareness
about the dangers of smoking and shaped public opin-
ion about tobacco-control legislation. It also provided a
venue for health advocates to broadcast special adver-
tisements with health messages, such as how to take the
steps to quit smoking.
Finally, democracy provided a window for the most

powerful tool in the fight against smoking: tobacco-
control legislation.
The Smoke Clears: Implementing
Tobacco-Control Measures
In 1991, legislation was brought to the Polish Senate,
which introduced a comprehensive set of tobacco-con-
trol measures based on the recommendations from the
1990 international conference and the WHO. The mo-
tion faced intense opposition from tobacco companies,
sparking a heated public debate that lasted several years.
Advocates consistently defended the bill by reiterat-
ing the scientific evidence of the public health threat of
smoking, while the powerful tobacco lobbies countered
by emphasizing their right to advertise freely and the
potential threat to Poland’s economy. The tobacco lob-
bies poured an unprecedented amount of money into
fighting the legislation, wielding a force as a special
interest never before seen in Poland. Media coverage of
the debates helped shape public opinion, which eventu-
ally swayed toward the health advocates—the “David”
against the “Goliath” tobacco lobby.
In November 1995, the Polish parliament passed the
“Law for the Protection of Public Health Against the Ef-
fects of Tobacco Use” with a huge majority of 90 percent
of the votes. The groundbreaking legislation included:
A ban on smoking and the sale of cigarettes in
health care centers, schools, and enclosed
workspaces
A ban on the sale of tobacco products to minors
under 18 years of age

A ban on the production and marketing of smoke-
less tobacco
•
•
•
A ban on electronic media advertising (includ-
ing radio and television) and restrictions on other
media
The printing of health warnings on all cigarette
packs to occupy 30 percent of at least two of the
largest sides of the packs—the largest health warn-
ings on cigarette packs in the world at that time
Free provision of treatment for smoking
dependence
The sweeping legislation has served as a model for other
countries. The European Union followed the Polish
precedent in 2003 and required similar health warn-
ings on all cigarette packs. In 1999 and 2000, the tax on
cigarettes increased 30 percent each year, and a total ban
on advertising was passed in 1999.a In just a few years,
Poland had transformed from one of the least favorable
climates in Europe for tobacco controls to one of the
most favorable.
According to legislation, Poland is required to dedicate
0.5 percent of all tobacco taxes to funding prevention
programs. In practice, the tobacco-control movement
has not received the full 0.5 percent allocation and con-
tinues to lobby the government for increased funds for

prevention programs. However, one recipient of tobacco
tax revenue, the Health Promotion Foundation, has led
health education and consumer awareness efforts with a
profound impact on smoking patterns in Poland. Since
the early 1990s, the foundation has launched an an-
nual campaign each November called the “Great Polish
Smoke-Out” to encourage smokers to quit. For a time,
the smoke-out, the largest public health campaign in
Poland, included a competition that invites Poles who
have quit smoking in the past year to send a postcard
for the chance to win a week-long stay in Rome and a
private audience with the Polish-born Pope John Paul
II. The campaign attracted extensive media attention
and uses television, radio, and print media to spread the
core messages of how and why to quit. Throughout the
year, health education promoted by schools, the Catho-
lic Church, and local civic groups has reinforced the
campaign’s messages.
a The impact of these additional measures is not captured
in this chapter.
•
•
•
The campaign is popular, and 80 to 90 percent of Poles
have heard of it. Each year, between 200,000 and 400,000
Poles credit the campaign with their successful quitting.
Since the first smoke-out in 1991, more than 2.5 million

Poles have permanently snuffed their cigarettes because
of the campaign.
Because raising tobacco taxes has long been recognized
as one of the most effective tobacco-control policy
interventions, health promotion foundations like the
one in Poland are becoming more common around the
globe. Increasing the price of cigarettes not only keeps
many from starting to smoke, but tobacco taxes can also
be a source of sustained funding for tobacco control
and other health promotion activities. Health promo-
tion foundations financed by these taxes are not limited
to supporting tobacco control: funds can also be used
to subsidize treatment for HIV/AIDS, tuberculosis, or
malaria; to conduct wider disease prevention and in-
formation campaigns; and to provide opportunities for
training or other capacity building for health profession-
als that are otherwise unavailable.
Tobacco Consumption and Cancer
Rates Plummet
Because of the extensive tobacco controls and the health
education efforts, far fewer Poles now smoke. Cigarette
consumption dropped 10 percent between 1990 and
1998. In the 1970s and 1980s, Poland had an estimated
14 million smokers, including 62 percent of adult men
and 30 percent of adult women. By the end of the 1990s,
this figure had dropped to less than 10 million Polish
smokers, with 40 percent of adult men and 20 percent of
adult women smoking.
The decline in tobacco use has led to a corresponding
improvement of health in Poland. The total mortality
rate in Poland, taking into account all causes of death,
fell by 10 percent during the 1990s. The decline in

smoking is credited for 30 percent of this reduction in
deaths, translating into 10,000 fewer deaths each year. At
the end of the 1990s, lung cancer rates in men aged 20
to 44 had dropped 30 percent from their peak levels just
a decade earlier and fell 19 percent in middle-aged men
between 45 and 64 years (see Figure 14–1). Decreased
smoking rates have contributed to one third of the 20
percent decline in cardiovascular diseases since 1991.
Infant mortality has fallen as well, and the percentage
of babies born with low birth weight has dropped from
over 8 percent in 1980 to less than 6 percent a decade
later. About one third of this reduced risk stems from
decreased smoking among pregnant women. In total,
life expectancy during the 1990s in Poland increased
by four years for men and more than three years for
women.13
Comparing the path of Poland with its neighbor Hun-
gary, a country that did not implement tobacco-control
measures, further illustrates the dramatic impact of
Poland’s efforts. In the 1980s, before Poland initiated
controls and health awareness campaigns, lung cancer
rates in the two countries were roughly equivalent.
Throughout the 1990s, lung cancer rates in Hungary
continued to climb, at the same time that they were
falling by one third in Poland; today rates in Hungary
have peaked at their highest levels ever for young and
middle-aged residents.
Figure 14–1
Standardized mortality rates
among Polish males, 1959–1999.
Source: Zatonski W, personal communication, July 2, 2004.

Aged 20 to 44
0
1
2
3
4
5
6
7
8
1
9
5
9
1
9
6
1
1
9
6
3

1
9
6
5
1
9
6
7
1
9
6
9
1
9
7
1
1
9
7
3
1
9
7
5
1
9
7
7
1

9
7
9
1
9
8
1
1
9
8
3
1
9
8
5
1
9
8
7
1
9
8
9
1
9
9
1
1
9

9
3
1
9
9
5
1
9
9
7
1
9
9
9
D
ea
th
s
pe
r
1
0
,0
0
0
D
ea

th
s
pe
r
1
0
,0
0
0
Aged 45 to 64
0
50
100
150
200
250
1
9
5
9
1
9

6
1
1
9
6
3
1
9
6
5
1
9
6
7
1
9
6
9
1
9
7
1
1
9
7
3
1
9
7

5
1
9
7
7
1
9
7
9
1
9
8
1
1
9
8
3
1
9
8
5
1
9
8
7
1
9
8
9

1
9
9
1
1
9
9
3
1
9
9
5
1
9
9
7
1
9
9
9
Box 14–1
South Africa’s Story
until the �990s, south africa’s tobacco industry—controlled

almost entirely by one company—exerted im-
mense power and operated virtually untouched by government
restrictions or taxes. The tobacco industry
was seen as a major source of government revenue, taxes, jobs,
and advertising dollars. The dominant
tobacco company, rembrandt, was established in �948, when
the national Party came to power, and was
seen as a symbol of afrikaaner success in business—and
therefore beyond question in policy debates
about tobacco. With strong ties to the media and the apartheid
government, nothing stood in its way.
When the african national Congress came to power in �994, the
antismoking movement gained a valu-
able ally in incoming President nelson Mandela. Mandela had
made his strong antismoking stance known
during World Tobacco day in �992 and through his call for a
“world free of tobacco.” unlike the previous
afrikaaner government, Mandela’s african national Congress
party had no ties to the tobacco industry and
placed a much higher priority on health care for all. The first
health minister of the new government, nkosa-
zana Zuma, was an ardent supporter of the tobacco-control
cause and fearlessly pursued the tobacco con-
trol that her predecessor rita Venter had begun, despite intense
opposition from the industry. even before
assuming office as the minister of health in �994, she
committed the african national Congress to take a
leadership role when she addressed the first all-africa Tobacco
Control Conference in Harare in �993.
despite the influence of the tobacco industry, public health
researchers worked tirelessly to bring atten-
tion to the dangers of smoking: Professor Harry sefterl’s work
from the �970s stimulated many to recog-
nize that unless action was taken, south africa faced pending

chronic disease epidemics. derek Yach, a
researcher who had established evidence on the economic and
health impacts of smoking, collaborated
in the mid-�980s with local civic groups such as the Tobacco
action group and international partners to
promote tobacco-control efforts.
The first major victory for the antitobacco movement occurred
in �995 with the passage of the Tobacco
Products Control act. The act introduced health warnings,
banned smoking on public transportation, and
established restrictions on youth under �6 purchasing
cigarettes. although relatively mild in reach, the
legislation was an important milestone because it was the first
schism between the government and the
tobacco industry.
The tobacco-control policies implemented in the second half of
the �990s were bolstered by research
at the university of Cape Town, which established the rationale
and evidence base for increased taxes
on smoking, considered by the group’s researchers to be the
most cost-effective and powerful way of
rapidly reducing smoking. studies demonstrated that because of
the sensitivity of demand for cigarettes
to changes in prices, an increase in prices would cause a decline
in consumption and at the same time
increase tax revenue. Health advocates argued that a tax
increase of 50 percent—in their view necessary
because the real value of taxes had fallen 70 percent between
�970 and �990—would lead to 400,000
fewer smokers and an increase in tax revenue of approximately
$92 million.14,15
in �997, taxes on cigarettes were increased by 52 percent, to
reach 50 percent of the value of the retail

price of cigarettes. between �993 and 200�, the real value of
cigarette taxes increased by 2�5 percent.
(continued on next page)
Strengthening Tobacco Controls
Worldwide
Both South Africa (Box 14–1) and Poland share a com-
mon lesson in battling tobacco. Once smoking is seen
for what it is—the leading cause of preventable deaths
among adults worldwide—then governments do act.
They do so with a set of tools that are powerful, cost-
effective, and save millions of lives.
Importantly, the national experiences of Poland and
South Africa have not remained confined to the two
countries. The leadership created in South Africa about
tobacco control was strengthened into global leader-
ship during five years of negotiations, which led to the
world’s first treaty for public health, the Framework
Convention on Tobacco Control. The South African
negotiating team played a decisive role in ensuring that
the most effective text was accepted first by African
countries—and that no watering down could be toler-
ated—and later by all 192 governments that adopted it
in May 2003.
In May 2003, all of WHO’s member states unanimously
adopted the convention, indicating their commitment to
stronger efforts to reduce tobacco use through many of
the same interventions that proved successful in Poland

and South Africa: health education, tobacco-control
legislation, cigarette taxes, warnings on cigarette packs,
restrictions on smoking in public places, and bans on all
cigarette advertising and promotion. By the end of 2006,
more than 130 countries had ratified the treaty and were
beginning to implement it. Although still in its early
days, the treaty has played an important role in changing
the way that most governments approach tobacco use.
References
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1.
2.
3.

4.
in �999, the Tobacco Products Control amendment bill was
passed, outlawing smoking in enclosed public
places, banning tobacco advertising and sponsorship, and
requiring explicit health warnings on all ciga-
rette packs.
The results of the price increases and control measures have
been striking. Cigarette consumption fell
from �.9 billion packs in �99� to �.3 billion in 2002—a
decline of more than 30 percent, peaking after
the �997 tax increases. The sharpest drops have been among
youth and the poor, two groups that are
most sensitive to changes in price. smoking prevalence among
youth has dropped from 24 percent in
�993 to �9 percent in 2000. at the same time that consumption
dropped, tax revenues in south africa
doubled since �994.
Yach has credited the mix of basic science and political
commitment with the passage of one of the
world’s most far-reaching tobacco-control policies. “You need
the right combination of science, evidence,
and politics to succeed,” he explained. “if you have one without
the other, you don’t see action.”16
Box 14–1
South Africa’s Story (continued)

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patterns of smoking and smoking-attributable mor-
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978-1-5386-5651-8/18/$31.00 ©2018 IEEE
Blockchain Challenges and Security Schemes:
A Survey
Sirine SAYADI
MEDIATRON Laboratory
Higher School of
Communication of Tunis,
[email protected]
Sonia BEN REJEB
Higher School of

[email protected]
Ziéd CHOUKAIR
Higher School of
[email protected]
Abstract With the increasing number of connected devices
and the number of online transactions today, managing all
these transactions and devices and maintaining network
security is a research issue. Current solutions are mainly based
on cloud computing infrastructures, which require servers
high-end and broadband networks to provide data storage and
computing services. These solutions have a number of
significant disadvantages, such as high maintenance costs of
centralized servers, critical weakness of Internet Of Things
applications, security and trust issues, etc. The blockchain is
seen as a promising technique for addressing the mentioned
security issues and design new decentralization frameworks.
However, this new technology has a great potential in the most
diverse technological fields. In this paper, we focus on
presenting an overview of blockchain technology, highlighting
its advantages, limitations and areas of application.
The originality of this work resides in the comparison
between the different blockchain systems and their security
schemes and the perspective of integrating this technology into
secured systems models for our comfort and our private life.
Keywords Blockchain, Security, Technology, Smart
Contracts, Consensus

I. INTRODUCTION
The current network model connects multiple computing
devices and will continue to support small-scale Internet of
Things networks that will not be able to meet the growing
needs of tomorrow's large ecosystems. Centralized cloud
servers will remain a bottleneck. throttling and a point of
failure that can disrupt the network.
In this context, Blockchain technology appeared in 2009
by Nakamoto [1] "Bitcoin Developers" as a storage
technology serving decentralized large registers and as a
security technique for authenticating, authorizing and
verifying data generated.
With blockchain technology the concept of consensus has
emerged as a mechanism that ensures trust in communication
between two entities without the intervention of an
intermediary. We can use blockchain in cryptocurrency,
smart contracts, digital identity management, internet of
things, access control applications, automated peer-to-peer
insurance, in banks and in many other applications [2].
Since its inception, from the initial cryptocurrency to the
current smart contract, blockchain technology has shown
promising prospects in many areas of application.
This proposed paper will be a state-of-the-art study on
blockchain technology. Section 2 will present an overview of
blockchain technology. Section 3 will describe a semantic
study of the potential of blockchain technology. We present
in Section 4 some cases of use of this technology. Then we
will examine the security threats, some real attacks for this
technology, and its security enhancement solutions in Section

5 and finally we will conclude our paper by suggesting future
directions.
II. OVERVIEW OF BLOCKCHAIN TECHNOLOGIES
This section presents a complete visualization of
blockchain technology, how it works, its structure and
existing types.
A. Blockchain Process
The Blockchain process is described as a transaction
between users on the network that are grouped into blocks.
The block is validated and saved on the network by a
«minor » according to cryptographic techniques that depend
on the rules of the type of blockchain used.
In the bitcoin blockchain this technique is called the
"Proof-of-Work", (POW), and "proof-of-stake" (POS) in the
blockchain ethereum. If the block is validated, it is time
stamped and added to the block chain. The transaction is then
visible to the receiver as well as the entire network. This
process takes some time depending on the blockchain (about
10 minutes for bitcoin, 15 seconds for Ethereum) [8].
Each blockchain is identified by its cryptographic hash
and carries a list of transactions and a hash to the previous
block.
The exception to this is the first block in the chain, called
"genesis", which is common to all clients in a blockchain
network and has no parent. This establishes a link between
the blocks, thus creating a chain of blocks, or blockchain.
Any node having access to this ordered and back-linked

block list can read it and understand what is the current
global state of the data exchange on the network.
Figure 1: Blockchain Process
B. Blockchain Structure
A block is composed of two main parts which are the
Block Header and the transactions (see Figure 1). The Block
header contains several fields, the most important among
them are the block version, the Merkle tree Root Hash, time
stamp, nBits, Nonce and parent block hash. Transactions are
the data saved in the block [46].
These fields will be detailed below (see figure 2):
Block Version: Specifies the set of block validation
rules to follow [46].
Merkle tree Root Hash : is a condensed digital
fingerprint of all transactions in the block. The slightest
modification of a transaction in the block modifies this root.
Its principle is to calculate the hash of a node from a hash of
his sons [3].
Timestamp: current time in seconds in universal
time since January 1, 1970 [46].
nBits: target threshold of a valid block hash.
Nonce: A 4-byte field, which usually starts with 0

and increases for each hash calculation. On receipt of the new
block, the complete nodes compute the header hash only
once, to see if the Nonce is valid [37].
Parent block hash: The nodes save the data of the
block's. Thus, all the nodes have the hash of the block 31, if
the block 32 is received by a node, it will determine that the
block 32 is the child of 31 by checking this field [37].
Figure 2: Simplified Block Structure
C. Type of Blockchain
There are three types of Blockchain technologies
presented in the following table :
Public blockchain from which everyone can
participate in the process of reaching consensus and
verifying the transaction. Like Bitcoin [4] and Ethereum [5].
Consortium blockchains: In this type, the node
can be chosen in advance if the data in blockchain can be
public or private. They can be considered as partially
decentralized like Hyperledger [6].
Private blockchain has strict management
authority over access to data. Nodes are restricted, not all
nodes can participate in this blockchain like Ripple [7].
Table 1: Comparative table of blockchain types [46]

All types of blockchain have advantages. The choice of
blockchain type depends on our needs and our proposed
services.
III. POTENTIELS OF BLOCKCHAIN
Blockchain technology is not only a technique, but it is a
technological revolution with very important security
features, its operating model using consensus and its shared
ledger to solve the problems of traditional centralized
models.
A. Basic Security Techniques
We detail in this section the different basic security
principle by specifying how Blockchain technology can
perfectly guarantee them.
Integrity: it to ensure that the information has not
been changed, only by those authorized to make
changes. Blockchain uses cryptographic mechanisms
to guarantee that operations are immutable with the
purpose of verifying integrity.
Availability: it ensures the availability of data for
every need. the service is always active at the request
of a legitimate users. Blockchain allows users to
maintain blocks in a decentralized manner with
various copies on the blockchain.
Pivacy: is the guarantee that only authorized persons

can access to the information. The Blockchain uses a
pseudo-anonymization mechanism (hash functions) to
hide user identities to ensure confidentiality.
Authentication: a procedure by which a computer
system certifies the identity of a person or a computer
to allow that person to access certain secure resources.
The Blockchain technology provides this function by
providing private keys for users who are authorized to
carry out transactions.
Non-repudiation: Is the impossibility, for a person or
any other entity engaged in a communication, to deny
having received or sent a message, and this is ensured
by blockchain technology.
B. Shared Ledger
This is the basic feature of blockchain technology, it
means that blockchain does not have a centralized node, data
is processed, stored and updated in a decentralized way. This
avoids the problems of single deffain point and offers a peer
to peer communication such that all nodes are interconnected
and all participants in the network are equal without a central
node.
C. Smart Contract
The smart contract is autonomous computer programs
that once started, automatically execute pre-defined
conditions with conditional statements of the type « if ....
Then .... » Using the information available on the blockchain.

These contracts must be able to reduce audit costs,
execution, arbitration and fraud. They may have to manage
funds or authenticate external entities [8].
D. Consensus
A consensus is a secure fundamental trust mechanism. It
characterizes a general agreement of existence of the
members of a group. It allows you to make a decision
without the need of an intermediary or a trusted authority.
In the existing blockchain system, there are several
consensus mechanisms. We will quote the best known
below:
PoW (Proof of Work) :
Method used to validate Blockchain network blocks. This
method requires users to use their computing power to
validate a block. Minors compete against each other. As a
result, the higher the computational power (combining
several computers, to increase computing power), the more
likely they are to find the result of a "Hash" function and thus
validate the block. In the Bitcoin blockchain it is necessary to
count a validation every 10 minutes approximately [9].
PoS (Proof of Stake):
A chance to validate a block is based on how much of a
stake (or cryptocurrency) the miners have. For example, if
you had 5% of the cryptocurrency, you could extract 5% of
all its transactions. People with more currency are thought to

be less likely to attack the network. Its operating principle
based on the richest person has more power in the network is
unfair because the power here depends on the balance held in
the account [46]. The PoS save more energy (reduces the
amount of calculation) but increases the flow. Unfortunately,
if the operating cost is close to zero, attacks could result.
PBFT (Practical Byzantine Fault Tolerance) :
The problem of Byzantine generals is a metaphor that
deals with questioning the reliability of transmissions and the
integrity of the interlocutors. A Byzantine fault is therefore a
failure that consists of the presentation of erroneous or
inconsistent information. The consensus "Practical Bizantine
Fault Tolerance" (PBFT) is a state machine replication
protocol that tolerates arbitrary, or "Byzantine" faults. It is
fault-resistant, fast, long-lived and an attack does not impact
its performance too much. This protocol consists of three
phases: pre-preparation, preparation & validation, it requires
3f + 1 replicates to tolerate f simultaneous Byzantine faults.
When a message is sent on the platform, the nodes retransmit
the transaction to all peers. If at least 2/3 of the nodes confirm
the validity of the transaction it is confirmed. The platform
allows users to transfer peer-to-peer ownership regardless
[46].
Many other consensus mechanisms can be found , such as
DPoS (Delegated Proof of Stake), PoB (Proof of Bandwidth)
[10], PoEt (Proof of Elapsed Time) [11], PoA (Proof of
Authority) [12], Ripple [48], Tendermint[49] etc. that are
used in some blockchain systems.
A comparison between some of the most used consensus
algorithms is presented in table 2 [46].
With these advantages presented in this section from the

basic security techniques, smart contracts, shared ledger and
the consesus, blockchain technology has attracted attention in
several areas..
In the next section, we will introduce some areas of use of
blockchain technology as a solution concept.
Table 2: Comparison between some consensus algorithms
Property POW POS PBFT
Identity
management
of nodes
Without
permission
Without
permission
With
permission
Energy saving No partial yes
Power
tolerated
<25%
computing
power
<51%
stake

<33,3%
Defective
replicas
Example Bitcoin Ethereum Hyperledger
IV. CASES USE OF BLOCKCHAIN AND APPLICATIONS
In our days, Blockchain technology is used in many
areas, not only in the financial application, but also in other
areas such as supply chain traceability, identity certification,
insurance, International payments, the Internet Of Things
and the protection of privacy etc [25, 26, 31, 32, 33,34].
We detail in this section some uses of blockchain
technology:
1) Digital Currency :
Several transaction systems have been built recently by
blockchain technology, which makes a revolution in digital
currency and online payment system. With these digital
currencies and the crypthography technique, transfers can be
made without the need of the central bank.
For example, we can send and receive bitcoins using
public keys, with all anonymity we can record transactions.

Several other cryptocurrency like ethereurm, ripple,
litecoin and etc [27].
2) Smart Contract:
Smart Contract is a digital contract that runs
automatically through a computer system. It controls the
digital assets of the user, by formulating a set of rules
containing the rights and obligations of the users. Smart
Contract is like an automatic trusting authority among
participants [28]. Ethereum is an open source blockchain
platform offering a decentralized virtual machine based on
the Smart Contract. To manage these contracts Ethereum
uses its digital currency called ETH, users can create many
applications, services or different contracts on this platform
[29].
3) Hyperledger :
Hyperledger is an open source blockchain platform,
launched by the Linux Foundation in December 2015 with
the aim of improving reliability and performance. It aims to
support global business transactions of large technology,
financial and supply chain companies etc [30].
4) Blockhcain To Ensure privacy, Access control and
Integrity

Protecting our personal information and our private life
is a challenge in our day. [35][36] uses blockchain
technology based POW in IOT applications to ensure
integrity and confidentiality. Blockchain can also be used for
access control. Just save the history daily in blockchain as a
signed transaction specifying public keys with access rights.
Only minors authetified with his private keys can include
this transactions in their blocks [37].
Based on blockchain technology, Ouaddah and al. [36]
presented the FaiAccess framework with its different parts to
allow users to control their data. Zyskind et al. [34]
exploited the access control option provided by the
blockchain with storage in a distributed hash table of several
selected nodes. The Blockchain is used here for data location
management and their access.
Ali and al. [33] used blockchain to build "Blockstack ID"
which is an identity system and a decentralized PKI. This
system consists of a control plane that is a name registration
protocol and links and a data plan that is responsible for
storing the data that must be signed by the name owner's
key.
5) Blockchain For Eletronic Transactions
The Blockchain can be used as a base that will support
the shared economy, based on machine-to-machine (M2M)
communication. Several propositions in the theme [38, 39,
40, 41, 42]. Blockchain technology allows agents to
autonomously perform a variety of transactions and to store

the history of each transaction with transaparance and no
deffiliation.
Sun et al. [41] specifies that Blockchain technology leads
to the Internet of decentralized and autonomous objects. The
blockchain supports all processing transactions between
devices and each device can manage its behaviors and roles
in an autonomous way.
Using the Bitcoin network, [40] described a model of
data exchange by electronic money, between a sensor and a
client. [38] described a Bitcoin-based e-commerce model for
IOT devices. This composite model consists of 4 layers (the
technical layer for the management of the Blockchain
module, the infrastructure layer containing the smart
contract platforms and IoT services, the content layer
containing the participants and the IOT products and the
layer exchange that contains the P2P transaction system).
We can find many other proposals that use Blockchain
technology for economic transactions for IoT like ADEPT
[43], Filament [39], Waston IoT platform [44], IOTA [42]
etc.
6) Blockchain To Secure Smart Home :
Dorri et al. [45, 50] proposed a lightweight blockchain
solution adopted for IoT without cryptocurrency to illustrate
a smart home containing a power computer that is
responsible to control and audit communications and provide
access control between devices. It maintains a private
blockchain and is considered minor without the need for the
proof of work concept because only this computer is

responsible for managing the blockchain. Other devices
receive a private key and a public key to perform
transactions. For example, if a sensor wants to open the
faucet, it will send a transaction to the faucet, which will
check in Blockchain if that sensor is allowed to open it.
A smart home is the best example for IoT Blockchain
combination. The services offered by blockchain technology
can be contribute to shared economies and to the smart
cities where objects connect seamlessly and anonymously to
exchange and share data.
V. SECURITY ISSUES OF A BLOCKCHAIN TECHNOLOGIE
We describe in this section some recently encountered
limitations that can affect the good functioning of
blockchain technology by presenting some models in the
form of the proposed improvement solutions to limit these
risks.
A. Risks to Blockchain
1) 51% Vulnerability:
The consensus mechanism has a vulnerability of 51%,
which can be exploited by attackers to manipulate the
blockchain.

In PoW, if the hash power of a minor> 50% of the
blockchain's total hash power, the 51% attack can be
initiated. As a result, mining resources concentrated in a few
mining pools can cause fears, as a single pool controls more
than half of all computing power [13].
In the PoS, if the number of cryptocurrencies owned by a
single by a single miner is greater than 50% of the total
blockchain. A 51% attack can occur which an attacker can
arbitrarily manipulate information from the blockchain [47].
An attacker can exploit this vulnerability to carry out
attacks; we will mention some of each after following [15]:
Run a double spending by modifying the
transaction data (same coins are spent multiples
times).
Change the order of transactions.
Prevent normal mining operations of other miners
(Denial of service attack).
2) Double Spending attack:
A customer provides a seller with a signed transaction;
the seller verifies the validity with a peer who confirms the
transaction. If the client is malicious, it can create a
conflicting transaction by generating a double spend (the
same crypto currency spent twice) and having it validated by
another peer before the first transaction has spread across the
network. Both transactions are therefore proposed for
mining. Depending on which will be treated first, it is this
truth that will be imposed on the entire network by
registration in one block and invalidate the other. In this

case, if the seller had delivered before validation by the
minor, he was robbed ... resulting in a double spending [14]
[47].
3) Smart Contracts Risks
Dependency of the transaction order:
In order to update the blockchain, in each era, each miner
will propose his own block. Since a block can contain
multiple transactions, the state of the blockchain can change
several times during an epoch.
This attack can be triggered if two successive
transactions of the same block invoke the same smart
contract. The order of execution of these two successive
transactions affects the final state because the execution of
the smart contract is associated with a single state [47].
The time stamp dependency:
Each block in the blockchain contains a timestamp field.
Some conditions for triggering smart contracts depend on
the timestamp, which is defined by the minor according to
the time of his local system. Smart contracts depend on time
stamp fields are vulnerable, if they can be changed by

attackers [47].
Under-Optimized Smart Contract :
The gas value corresponds to the computing resources
exploited by the bandwidth operation, memory occupancy
and many other parameters used in Ethereum as a function
of time.
We can find some resource-intensive operations such as
dead code operations and the use of loops by exchanging the
gas value according to the cryptocurrency. [47].
4) Denial Of Service Attack
An attacker can launch a DoS (Denial of Service) attack
by exploiting a set of operations executed in a single
transaction. This is because some heavy operations require
too low gas values. This can cause a waste of resources [16].
5) Selfish Mining Attack:
This attack is conducted by mining in order to obtain
undue rewards or to waste the computing power of honest
minors [18]. The attacker holds the blocks discovered in
private and then tries to forge a private channel. The authors
in [19] proposed a Selfish-Mining attack, which attract other
honest miners to dispel their computing resources

unnecessarily to keep working on blocks that lead to a
stalemate instead of attaching them to the longest chain.
6) Reentrancy Attack:
It is the fact of exploiting a recursive sending for
example the biggest flight about 60 million US dollar of the
contract CAO by this attack just after its deployment of 20
days [17].
7) Liveness Attack
In [20] the authors proposed this attack to exploit the
dilation of the confirmation duration in order to obtain a
target transaction.
8) The Balance Attack
Christopher and al. [21] proposed this attack based on
PoW blockchain, which consists of identifying subgroups of
miners with similar mining power and delaying messages
passed between them in order to mine blocks before them.
B. Security Improvements
1) Smart Pool

L. Luu et al [22] proposed a new Smart Poll mining pool
system, implemented as a smart contract. It is a
decentralized mining protocol that replaces the centralized
pool operator.
It retrieves client transactions that contain information
about mining tasks. Then the miner performs a hash
calculation and returns the completed shares to the
smartpool. A threshold sets an amount, if the shadow of
actions made reaches this threshold, the miners will be
committed to a smartpool contract that verifies the actions
and delivers rewards to the customer [47].
2) Quantitative Framework
In [23] the authors proposed a quantitative framework is
used to analyze the performance and security provisions of
the blockchain. it is a blockchain simulator and a security
model that mimics its execution to evaluate basic security
and performance.
This model specifically focuses on the attacks of selfish
and double-spending mining by taking into consideration the
consensus protocol used and network parameters such as
block propagation delays, block sizes, delays network, block
rate and the mechanism of propagation of information etc.
3) Oyente

Loi and al. [24] proposed a new program called Oyente
that tracks errors in smart contracts. This tool can also detect
bugs and injection attacks in smart contracts.
Oyente analyzes the bytecode of smart contracts and
follows the EVM execution model [47].
VI. CONCLUSION AND PERSPECTIVES
In this paper, we presented an overview of Blokchain
technology. We have described its different security
potentials by specifying a comparison between some of the
most widely used consensus algorithms in different
blockchain systems. We have also clarified the fields of use
of this technology because in recent years, it has shown its
potential in several applications and this is due to the
advantages of this technology and its decentralized nature.
These applications permeate everyday life, business and
society as a whole, transforming the world into a more
efficient world. And finally, we indicated that many
maneuvers of this technology, then specifying the
improvement solutions proposed to defend them.
Blockchain then presents many promising opportunities
that open up many paths for the future and for a connected
world in complete security. However, the challenges remain
in the resources and consensus models used.
That's why, we aims in future work to leverage the
benefits, limitations of blockcahin technology, and
enhancement solutions to produce a new secure system

model that integrates this technology with the Internet Of
Things technology for a connected and secure world.
REFERENCES
[1] S.Nakamoto, Bitcoin,Apeer-to-peer electronic cash system,
2008,
https://bitcoin.org/bitcoin.pdf.
[2] M. Pilkington, Blockchain technology: principles and
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research handbook on digital transformations, F. X. Olleros
andM.
Zhegu, Eds., 2016.
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Application of Cryptographic Techniques.
[4] https://www.bitcoin.com/.
[5]
[6]
Workshop on Distributed Cryptocurrencies and Consensus
Ledgers,
2016.
[7]
Browser DownloadThis Paper, 2015.
[8] A. Kosba, A. Miller, E. Shi, Z. Wen, and C. Papamanthou,

Hawk:
The blockchain model of cryptography and privacy-preserving
smart
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(SP'16),
pp. 839-858, May 2016.
[9] Z. Zheng, S. Xie, H.-N. Dai, H. Wang, Blockchain
challenges and
opportunities: A survey, in: International Journal of Web and
Grid
Services, 2016.
[10] M. Ghosh, M. Richardson, B. Ford, R. Jansen, A torpath to
torcoin,
proof-of-bandwidth altcoins for compensating relays (2014).
https://www.smithandcrown.com/open-research/a-torpath-to-
torcoin-
proof-of-bandwidth-altcoins-for-compensating-relays/.
[11] Intel, Proof of elapsed time (poet) (2017).
http://intelledger.github.io/.
[12] P. technologies, Proof of authority chains (2017).
[13] N. Hajdarbegovic, Bitcoin miners ditch ghash.io pool over
fears of
51% attack (2014). http://www.coindesk.com/bitcoin-miners-
ditch-
ghash-io-pool-51-attack/
[14] M. Rosenfeld, Analysis of hashrate-based double
spending," CoRR,
vol. abs/1402.2009, 2014.
[15] Dean, 51% attack (2015). http://cryptorials.io/glossary/51-
attack/

[16] B. Rivlin, Vitalik buterin on empty accounts and the
ethereum state
(2016). https://www.ethnews.com/vitalik-buterin-on-empty-
accounts-
and-the-ethereum-state.
[17] N. Atzei, M. Bartoletti, T. Cimoli, A survey of attacks on
ethereum
smart contracts (sok), in: International Conference on Principles
of
Security and Trust, 2017, pp. 164-186.
[18] S. Solat, M. Potop-Butucaru, Zeroblock: Preventing selsh
mining in
bitcoin, Ph.D. thesis, University of Paris (2016)
[19] I. Eyal, E. G. Sirer, Majority is not enough: Bitcoin mining
is
vulnerable, in: Financial Cryptography and Data Security - 18th
International Conference, Lecture Notes in Computer Science,
2014,
pp. 436-454.
[20] A. Kiayias, G. Panagiotakos, On trees, chains and fast
transactions in
the blockchain, 2016. https://eprint.iacr.org/2016/545.pdf.
[21] C. Natoli, V. Gramoli, The balance attack against proof-of-
work
blockchains: The r3 testbed as an example, in: arXiv
preprint:1612.09426, 2016.
[22] L. Luu, Y. Velner, J. Teutsch, P. Saxena, Smart pool:
Practical
decentralized pooled mining, USENIX Security Symposium,

2017.
[23] A. Gervais, G. O. Karame, K. Wust, V. Glykantzis, H.
Ritzdorf, S.
Capkun, On the security and performance of proof of work
blockchains, in: The ACM SIGSAC Conference on Computer
and
Communications Security, 2016, pp. 3-16.
[24] L. Luu, D.-H. Chu, H. Olickel, P. Saxena, A. Hobor,
Making smart
contracts smarter, in: The ACM SIGSAC Conference on
Computer
and Communications Security, 2016, pp. 254-269.
[25] L. Luu, V. Narayanan, C. Zheng, K. Baweja, S. Gilbert,
and P.
Saxena, A secure sharding protocol for open blockchains," in
Proceedings of ACM SIGSAC Conference on Computer and
Communications Security (CCS'16), pp. 17-30, New York, NY,
USA,
2016.
[26] W. T. Tsai, R. Blower, Y. Zhu, and L. Yu, A system view
of financial
blockchains," in IEEE Symposium on Service-Oriented System
Engineering (SOSE'16), pp. 450-457, Mar. 2016.
[27] https://fr.investing.com/crypto/
[28] A. Kosba, A. Miller, E. Shi, Z. Wen, and C. Papamanthou,
Hawk:
The blockchain model of cryptography and privacy-preserving

smart …
The Final Portfolio Project is a comprehensive assessment of
what you have learned during this course.
The Final Project has two parts: Limitations of Blockchain and
Emerging Concepts.
Blockchain continues to be deployed into various businesses
and industries. However, Blockchain is not without
its problems. Several challenges have already been associated
with the use of this technology. Identify at least 5 key
challenges to Blockchain. Additionally, discuss potential
solutions to these challenges. Lastly, please discuss if we will
see the limitations to blockchain be reduced or mitigated in the
future.
There are several emerging concepts that are using Big Data
and Blockchain Technology. Please search the internet and
highlight 5 emerging concepts that are exploring the use
of Blockchain and Big Data and how they are being used.
Conclude your paper with a detailed conclusion section which
discusses both limitations and emerging concepts.
The paper needs to be approximately 8 pages long, including
both a title page and a references page (for a total of 10 pages).
Be sure to use proper APA formatting and citations to avoid
plagiarism.
Your paper should meet the following requirements:
• Be approximately 8 pages in length, not including the required
cover page and reference page.
• Follow APA7 guidelines. Your paper should include an
introduction, a body with fully developed content, and a
conclusion.
• Support your response with the readings from the course and
at least five peer-reviewed articles or scholarly journals to
support your positions, claims, and observations.
• Be clear with well-written, concise, using excellent grammar
and style techniques. You are being graded in part on the
quality of your writing.

NO PLAGARISM and need plagiarism report for this task
please
Source:-
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6bb2c48/6322713?response-cache-control=private%2C%20max-
age%3D21600&response-content-
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SHA256&X-Amz-Date=20200614T000000Z&X-Amz-
SignedHeaders=host&X-Amz-Expires=21600&X-Amz-
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-east-1%2Fs3%2Faws4_request&X-Amz-
Signature=6ac5cf3ec64f59cdd7959ad98adeb4e1f08ac5ed164679
a331c6b0d2cb77bea7
History has shown that innovations in various technologies
spread at such a rapid pace among consumers and communities
that the latter hardly paid a more serious attention to existing
flaws and limitations of these innovations. Quite similar is the
case with blockchain technology. Only through trial and error as
well as through research and development experts in the field
were able to understand its current issues and limitations.
The main limitation to Blockchain technology is its complexity.
As you will see in this week’s lecture and PowerPoint, there are
other limitations as well. Please be sure to review the readings
for the week to get a better understanding of the limitations and
challenges. We are close to finishing the term, so please be sure
to review any past readings on blockchain to ensure you have a
deep and solid understanding of blockchain.

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