CRYPTOCURRENCIES A comparison between the three leading

cryptocurrencies and their properties.

Ove Person IKT411 Advanced Project

1

Abstract A cryptocurrency is a decentralized digital payment system widely used today. The leading scheme

Bitcoin has an estimated market value of more than 7 billion US dollars. This report will take a look at

how exactly the cryptocurrency network is set up and how it is based on mistrust. I will list basic

features common to most types, as well as more specific mechanics that are related to cryptology

principles.

I will also describe the three leading cryptocurrency schemes today, Bitcoin, Litecoin and Peercoin, and

compare them to each other. I will discuss the security and privacy aspects of the respective schemes,

and explain where these come in to use. I will also point out the schemes regard security on different

levels, and that since the network is copied and synchronized among all the miners this can inflict

security.

Preface This report is written by the ICT Security student Ove Person over the duration of circa four months in

the spring of 2014. It is a part of the ICT-course “Advanced Project” (IKT411) at the University of Agder.

It was suggested and supervised by Prof. Vladimir A. Oleshchuk, and accepted by course lecturer Jan

P. Nytun.

Ove Person

Grimstad, 4th of June 2014

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Contents Abstract ................................................................................................................................................... 1

Preface ..................................................................................................................................................... 1

Tables ...................................................................................................................................................... 3

Figures ..................................................................................................................................................... 3

1 Introduction ..................................................................................................................................... 4

1.1 Background .............................................................................................................................. 4

1.2 Problem statement .................................................................................................................. 4

1.3 Assumptions and limitations ................................................................................................... 4

1.4 Report outline.......................................................................................................................... 4

2 Cryptocurrency ................................................................................................................................ 5

2.1 Miners ...................................................................................................................................... 5

2.2 Wallets ..................................................................................................................................... 5

2.3 Public ledger (Block chain) ...................................................................................................... 5

2.4 Transactions and confirmation ................................................................................................ 6

3 Crypto mechanics ............................................................................................................................ 7

3.1 Digital signatures ..................................................................................................................... 7

3.2 The block chain ........................................................................................................................ 8

3.3 Proof of work protocol ............................................................................................................ 8

4 Types of cryptocurrency schemes ................................................................................................... 9

4.1 Bitcoin ...................................................................................................................................... 9

4.2 Litecoin .................................................................................................................................. 10

4.3 Peercoin ................................................................................................................................. 10

5 Comparison ................................................................................................................................... 11

5.1 Litecoin – Reduced transaction confirmation time ............................................................... 11

5.2 Litecoin – Scrypt algorithm .................................................................................................... 11

5.3 Peercoin – Proof of stake ...................................................................................................... 12

5.4 Peercoin – Energy consumption ............................................................................................ 12

6 Discussion ...................................................................................................................................... 13

6.1 Proof of stake ........................................................................................................................ 13

6.2 51% attack ............................................................................................................................. 13

6.3 Mining pools .......................................................................................................................... 14

6.4 Cryptocurrencies are volatile ................................................................................................ 14

6.5 Anonymity ............................................................................................................................. 14

7 Conclusion ..................................................................................................................................... 15

8 References ..................................................................................................................................... 16

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Tables Table 1: Comparison of cryptocurrency features .................................................................................. 11

Figures Figure 1: Transaction and confirmation .................................................................................................. 6

Figure 2: Key pair and signature relationship [4] .................................................................................... 7

Figure 3: A typical digital signature [4] .................................................................................................... 7

Figure 4: The block chain [4] ................................................................................................................... 8

Figure 5: Logos of the respective cryptocurrencies ................................................................................ 9

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1 Introduction This report is for the master course ICT411 at Universitetet i Agder. My supervisor Prof. Vladimir A.

Oleshchuk suggested it as a potential task for the course. I found the task interesting, so I picked it for

the project and confirmed it with my course lecturer.

1.1 Background There are several hundred different cryptocurrency variations to choose from today [1]. They have

been around for approximately five years, and has had an increasingly bigger and bigger impact on the

digital market as they grew in popularity. As it stands today, the top three leading cryptocurrency types

have a total market value (released coins in circulation) of about 7.7 billion dollars [2]. Many also have

their own open-source communities that provide the continued development and supervision they

need. This ensures that the currencies remain useable and reliable for users.

1.2 Problem statement My task involved looking at cryptocurrencies as they stand today. I was to describe and compare

existing cryptocurrencies and explain how they work. In addition, I was to look at the security/privacy

aspects to find out just how safe they were to use.

My three problems I listed as following:

Describe the crypto mechanics in cryptocurrencies

o What are cryptocurrencies, how do they work?

o What kind of cryptography principles do they implement?

Describe and compare the top three cryptocurrencies

o What are the three leading cryptocurrencies?

o How do they differ from each other?

Discuss their security/privacy aspects (hashing, anonymity (?) etc.)

o What types of security principles do they offer?

o What level of anonymity do they offer?

1.3 Assumptions and limitations My project problem is quite specific, making my plan for work quite clear. Still, I will make a short list

of my assumptions and limitations.

I present the report assuming the reader has an idea of the technologies described.

When looking at the leading cryptocurrencies I limit myself to the top three most used

schemes.

I will ignore Ripple, as it is not a proper cryptocurrency scheme (it merely shares some of the

same principles).

I will limit my report to give an overview of the technology of cryptocurrencies, and from there

work on the underlying details.

1.4 Report outline I structured my report as close to the UIA standard [3] as possible, yet that it still answer the tasks

presented. I first present the mechanics behind cryptocurrencies, and explain how they work. Then I

list the top three leading cryptocurrency types, and compare them. Finally, I will discuss the security

aspects in cryptocurrencies and conclude the report.

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2 Cryptocurrency A cryptocurrency is a digital currency that utilizes cryptography principles in its operations. These types

of currency systems are generally decentralized and distributed, meaning all the users share and run

it together. What separates this currency from standard cash (fiat) currency is that its production is

not regulated or controlled by any authority, for instance a government.

The system is based around not trusting any of the fellow users. This “paranoid” feature allows each

user to have his own copy of the transactions log, so we can look at it any time we want. The “Crypto”

part of the cryptocurrency system involves encrypting the transactions, using digital signatures and

decrypting hash challenges to support the network.

To have a functioning cryptocurrency system that supports payment transactions, you need users,

miners, wallets and a ledger.

2.1 Miners A user can install a “miner” on their computer to mine for coins donated by the system regularly,

effectively trading computing power for a chance to get coins. The miner is a client program that

handles transactions in the network by reverting a hash function given by the sender to validate it. By

validating these transactions, miners then have a chance to receive coins generated by the system.

This I explain more in detail in section 3.3.

2.2 Wallets Users also need wallets to be able to trade coins, acting as their personal bank that holds them. These

wallets are the part of the system that allows users to send and receive coins in a simple manner, and

are a part of the local user side. I explain these in detail in section 3.1.

2.3 Public ledger (Block chain) In the middle of the cryptocurrency network lies is the block chain (often called the public ledger),

which records all transactions that happen. This is a record that all miners carry a copy of, and

approximately every ten minutes agree on updating and synchronizing. The ledger does not list all

people’s transactions; instead, it holds a history of all bitcoin transactions ever made to ensure that

the sender actually has the money promised. I explain more details in section 3.2 and 3.3.

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2.4 Transactions and confirmation When a user pays for something with bitcoins, the

user starts by sending out an announcement to all

the neighboring nodes (which they propagate

forward). The payer signs this message so that the

verifying nodes (miners) can check the sender and

that he has the coins to spend. If the payer checks

out, the node begins working on the proof-of-work

sent by the payer. This proof is an encrypted hash

that requires significant computation power to

reverse, ensuring that the reply of the completed

reversal is given by a reliable source.

This ensures safe practice in the network, as frauds

would have to invest too much computing power in

it to get any useful results. The result of the

reversed hash is broadcasted to the bitcoin

network, acknowledging the payment and telling

everyone to add it to their memory pool (the short-

term local storage of the block chain). When block

is accepted by the system, the transaction is

considered to have one confirmation. The process

is depicted in Figure 1.

Figure 1: Transaction and confirmation

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3 Crypto mechanics The cryptocurrencies I list in this report all use cryptography principles very similarly. Thus, I will first

explain the main components they have in common. The main cryptology mechanics in my described

cryptocurrencies are the digital signatures used in transactions, and the hashing algorithm used to

maintain and build the block chain.

3.1 Digital signatures We can use private-public key pairs to encrypt communication. They work by allocating the private key

to the user himself, and then having the public key out and open for everyone to use. If somebody

wishes to send something to a user, they would encrypt it with his public key and send it to him as a

resulting ciphertext (the outcome of the encryption). Since only the user himself has the private key,

only he can make use of the ciphertext. Even if a man in the middle were to pick up the message, he

would only find scrambled information and would need the private key to unlock it.

You can also use private-public key pairs to digitally sign a message. Since the user has his private key

that only he alone can use, he can use this to prove his identity. By encrypting a message with his

private key and sending it to whomever requests the proof, the receiver can verify the identity by

decrypting the message with the public key (as shown in Figure 2). The result is that the sender has

proven his identity because no one else but the user with the private key can do this.

Figure 2: Key pair and signature relationship [4]

In cryptocurrencies, we use digital signatures in the transactions so that the payer and the receiver can

verify each other. This ensures that only the relevant parties are involved in the transaction, and that

identities cannot be mistaken or abused. This is also reinforced by the key generation itself. A

cryptocurrency wallet can generate a key pair as often as necessary, and each key pair is unique (the

wallet generation allows for up to 2160 different keys) [4]. Key encrypted messages can also not be

modified because any change in the content would entirely change the resulting ciphertext, making

the decrypted result obviously changed. All these different features ensures a viably safe transaction

session.

The signature is usually created by combining a unique message and the private key of the user, and

encrypting them into a resulting ciphertext as shown in Figure 3.

Figure 3: A typical digital signature [4]

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3.2 The block chain The cryptocurrency system regularly processes transactions in “blocks” that are groups of unprocessed

transactions. On average, about every ten minutes one block is added to the block chain, a continuous

line of ordered transactions. Each new block is added on top of the previous along with a reference to

the previous block (see Figure 4), which makes it near impossible to modify (and abuse) without

invalidating the blocks around it making it obviously tampered with. As all miners have each their own

copy of the transaction records, they can always check for irregularities like these and normally every

time a new miner starts up, it does exactly that.

Figure 4: The block chain [4]

3.3 Proof of work protocol When adding a block to the block chain, a miner must provide a suggestion block, as well as a solved

hash digest to be included if the block is accepted. The digest is a returned challenge that the miner

reverted from its original hashed state. This challenge is sent out from the user wishing to perform the

transaction, and is called a “Proof-of-work”.

We use the Proof of work (POW) when the system wants to find out which block will be the next to

add to the Block chain. The mathematical hash function has to be brute force guessed, meaning you

try all combinations until you find one that fits. This ensures that different people solve it on a regular

basis, because if only one miner were to work on it, it would take an immense amount of time. In

contrast, when the whole network works on the same problem in parallel the chance increases more

realistically, and as mentioned orients around a working time of about ten minutes.

When the miner is asked to solve the hash, it is typically asked to find a hash digest output that starts

with a fixed set of binary zeroes. For instance, the miner will be provided a hash that starts with 20 bit

zeroes, and will be asked to hash different inputs until it matches the digest with a minimum of 20 bit

zeroes sufficiently (or until another miner has already done so). Note that in many cases it does not

have to be explicitly alike, just close enough.

9

4 Types of cryptocurrency schemes There are many motivations for creating a cryptocurrency, examples of which include technical

improvements such as efficiency and speed, potential governmental adoptability and even internet

culture phenomenon’s. The cryptocurrency Bitcoin has experienced a lot of success since its release,

growing in the digital transaction market. Therefore, the people interested in making an alternative

cryptocurrency used the same ideas.

The alternatives to Bitcoin are mostly variations and modifications of the open source bitcoin code.

The more successful new types of cryptocurrencies have been the ones that had a significant feature,

providing a different but viable alternative to Bitcoin. The top three leading cryptocurrencies are

Bitcoin, Litecoin and Peercoin (Figure 5).

Figure 5: Logos of the respective cryptocurrencies

4.1 Bitcoin The most notable cryptocurrency is Bitcoin [5]. This digital currency is the most dominant by far [2],

leading by market value and users. Considered the first cryptocurrency, Bitcoin was released open

source by the anonymous Satoshi Nakamoto in 2009 and implemented shortly after by collaborators.

Bitcoin did not achieve popularity for a few years until early 2013, when it exponentially grew in use

and became the most common renowned digital currency.

Bitcoin first introduced the idea of a payment network with transactions that is available for everyone

to see. This idea disregards trust between users, and allows for users to security check the system for

themselves. Bitcoin is also considered to be the first digital cryptocurrency that solved the problem of

double spending, by enabling random miners in the system to confirm transactions. This effectively

lowered the chance mathematically of being the miner solving the hash and thus being in a position to

use this.

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4.2 Litecoin Litecoin [6] is a cryptocurrency alternative to Bitcoin which is very similar, yet it offers different

features. Litecoin adds blocks to the block chain on average every 2.5 minutes, unlike Bitcoin that adds

blocks on average every 10 minutes. Litecoin also uses an alternative hashing type than Bitcoin known

as Scrypt.

In the cryptocurrency market Litecoin is the runner up to Bitcoin, placing as the second most popular

and used coin [2]. It was released in 2011 by former Google employee Charles Lee, with the goal to be

an alternative to Bitcoin. Litecoin did not achieve escalated user adoption until early-mid 2013, when

Bitcoin and cryptocurrencies in general became recognized as a viable currency.

Litecoin is very similar to Bitcoin, because it in practice is the same system and utilizes the same

network principles. It has a public ledger that logs all transactions, it offers a miner client to all its users,

and it uses a wallet to hold coins and has its strength in the vast distributed network. Litecoin does

however offer its own unique strengths. The block chain adds a block on average four times as often

as bitcoin. This means that the block chain is a lot longer, giving clients more transaction history and

having a lot more coins in circulation. Litecoin also offers a greater amount of total coins available for

mining, as it allows for up to 81 million litecoins to exist (almost four times as much as bitcoin).

4.3 Peercoin Peercoin [7] is a deviation of Bitcoin much like Litecoin, in that it is an extension of the Bitcoin code

and principles. Peercoin focuses on its own unique type of security, which is a hybrid of Bitcoins proof-

of-work and a lesser-known proof-of-stake method. Peercoin also uses less energy to maintain, making

it the first environmentally friendly cryptocurrency option.

This cryptocurrency is the third most used coin on the market, succeeded only by Bitcoin and Litecoin

respectively [2]. Peercoin was developed and released in 2012 by the authors Scott Nadal and Sunny

King (a pseudonym), but did not achieve much popularity until 2013 when cryptocurrencies became a

popular digital payment method.

Peercoin distinguishes itself by not only using proof-of-work scheme, but also by using the proof-of-

stake scheme, offering several different features (see sections 5.3 and 6.1).

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5 Comparison Litecoin and Peercoin are quite similar to Bitcoin; this is because they originate from bitcoins source

code. Considering that the creators chose to keep them similar, they share many common elements

such as a public ledger to log the transactions, miners to maintain the network, and cryptology

principles.

Bitcoin Litecoin Peercoin

Public release year 2009 2011 2012

Current coin

market cap*

$ 7,776 million $ 322 million $ 47 million

Coins released* 12,8 million 28,8 million 21,4 million

Use of Miners Yes Yes Yes

Use of Public ledger Yes Yes Yes

Avg transaction time 10min 2.5min 10min

Hashing algorithm SHA-256d Scrypt SHA-256

Proof of work Yes Yes Yes

Proof of stake No No Yes

Table 1: Comparison of cryptocurrency features

*Rough estimate May 2014 [2]

It is important to note why Litecoin and Peercoin are the cryptocurrencies that are so close to the

leading position of Bitcoin; they both offered a set of unique features that made them a viable option

to bitcoin. Thus, I will compare the two respective cryptocurrencies to bitcoin when listing their

differences.

5.1 Litecoin – Reduced transaction confirmation time Litecoin has an average transaction time for all transactions about 2.5 minutes long [8]. This means in

practice that each block of transactions is added to the block chain (its public ledger) about four times

as often as Bitcoin. What is important to note is that this means block confirmations will be given

faster, and for those who wish to wait or check as few blocks as possible (say fast transactions vendors),

they have this option with Litecoin. In comparison, Bitcoin forces all users to have to wait ten minutes

to have them confirmed, though this also means considering the computing power of the bitcoin

network, that these replies are more reliable. An also important note is that Litecoin retargets the

block difficulty every 3.5 days, instead of Bitcoins 7 days.

5.2 Litecoin – Scrypt algorithm Litecoin also uses scrypt for its hashing algorithm, unlike Bitcoin that uses SHA-256d. Scrypt needs a

lot of memory to be brute forced, making it very hard to parallel process like SHA-256. This is because

scrypt was designed as a security hash that resists brute force attacks, by increasing the hardware

requirements needed to break it. In Bitcoin it is not uncommon to mine with Application-specific

integrated circuits (ASICs), which in short are specialized parallel processing hardware units used

specifically for one purpose (in this case mining). With scrypt as the hashing algorithm, Litecoin levels

the playing field in for its miners, unlike Bitcoin. This way users with more standard GPUs can compete

with ASICs.

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5.3 Peercoin – Proof of stake Peercoin uses POW much like Bitcoin, but it uses it in a combination with a different mining method

called Proof of Stake (POS). This mining method requires proof that you carry Peercoins to be able to

mine – you prove that you have a stake in the network health. This means that only users with

peercoins in their wallets can mine, denying plain mining (as in for example Bitcoin, where you can

mine without having any coins). The mining is also regulated around your amount of coins, meaning

that the more peercoins you have the more you can mine. This simulates a type of interest in holding

peercoins, and is suggested to be a better long-term solution than the one that bitcoin uses currently

[9].

5.4 Peercoin – Energy consumption Because Peercoin uses POS, it is a more energy efficient solution compared to alternatives like Bitcoin.

Bitcoin is regarded as a digital currency that wastes more energy than necessary [10], and Peercoins

POS provides an arguably better alternative. This is because POS requires less energy to perform than

POW. As POW is based around reverting hashes, it requires a lot of energy to decrypt them as they are

designed to brute force it until it finds a solution (about every ten minutes). By comparing the energy

consumption of POW with POS, you find that because POS merely runs in the Peercoin client and

handles payments for fees, it uses over all less energy. So far, Peercoin has been registered to use just

30% of the energy that Bitcoin uses [7].

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6 Discussion In this chapter, I will discuss the security and privacy aspects of the cryptocurrency schemes I have

examined. I will discuss the uncertain necessity of the Proof of stake modification, as well as its ability

to prevent the 51% attack and its long term complementing attributes. I will also discuss the problem

with mining pools, the volatility of cryptocurrency funds and the anonymity that the cryptocurrencies

provide.

6.1 Proof of stake The necessity for POS has been debated among cryptocurrency users, as they are unsure if the problem

that Peercoin fixes with POS really is there. Bitcoin relies solely on POW mining, and plan to keep using

it during its lifetime as a currency. For the time being there are no direct negative effects with using

this approach, though it has been debated that it uses unnecessary large amounts of energy (see

section 5.4) and that it has shortcomings in long term use.

Over time bitcoin mining profits are reduced because of its intended deflation effect, resulting that

miners over time will get smaller and smaller rewards. Users have speculated that this might inflict the

later mining incentive over time [9], when miners have to invest a lot of hardware to have a chance to

compete for the reward, not to mention that the reward will be so low. This might even lead to miners

moving to another cryptocurrency, potentially one that use POS. Peercoins long-term solution

POW/POS changes this by having miners initially mine for a reward (POW), but also allow them to earn

interest in their holdings over time (POS).

In the long term it might help to migrate your values from Bitcoin to Peercoin as a user considering

POS use, especially since they already have a basis for users to use the POS part and receive interest.

However, Bitcoin will keep rewarding mining all the way to the year 2140 [11] before it stops entirely,

and it has a more stable and bigger user network. For the time being there is little reason to start using

Peercoin if you are a user of Bitcoin, and there is no guarantee that cryptocurrencies will stay as

influential as they are currently, in the years ahead.

6.2 51% attack POS can cover the vulnerabilities that could potentially occur in a proof-of-work system, a 51% attack

[12]. The proof-of-work system could in theory be circumvented if one entity were to possess more

than half the network power (51% or more). If one collected entity had this much it would generally

solve most of the occurring blocks in a row, and thus could control spending and decide which money

that were spent or not.

This is something that Peercoin does not allow to happen, as miners (users) who confirm transactions

have to prove that they own an amount of Peercoins. This results in it becoming exponentially more

difficult to attain that 51% of the market as an abuser, not to mention that his own peercoins would

decrease in value when buying up more of them making the effort quite futile.

Though a 51% attack could potentially be performed on the Bitcoin system, it would be near impossible

to do in reality. To put it in perspective, it has been argued that not even the collective computer power

that Google currently controls would be able to reach a 51% of the Bitcoin system [4]. So bitcoins are

still considered safe to use, without a risk of such an attack at this time.

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6.3 Mining pools As cryptocurrencies arose to popularity of the last few years, so did the idea of collecting mining power

together to mine as a single entity. This presents a challenging risk, as the greater a mining pool

becomes, the more impact it has on the global mining. For instance, the “BTC Guild” has solved six

blocks in a row in the bitcoin system [4]. Had it not been for them limiting their member numbers, they

could potentially have a great security impact on the network, allowing them to modify blocks and

transactions if they wanted to.

6.4 Cryptocurrencies are volatile The cryptocurrency schemes I have mentioned in this report all use public-private key pairs when

paying from one user to another (see section 3.1). The users access their funds through the private

keys, kept in their digital wallets stored on their local hard drives. Since the key pairs are something

that the user controls himself, the network cannot check them or back them up in any way (this would

also compromise their security). Thus, the user has total responsibility in ensuring their safety on his

own drives. If the keys were to be compromised the user would not be able to get them back, and he

would get no type of compensation back from the system (as it is not represented by any group, like

for instance PayPal) [4].

Therefore, the entire security of his funds rests on the security of the drives. A user who wants to

actively protect his funds would have to protect himself against active cyber-attacks (to either steal or

corrupt the funds), and hard drive failures (which is a realistic problem that can happen to any drive).

A necessary prevention for users would be to use bitcoin anonymously (accessing it through an IP

masking service like Tor), and having backups for their wallets (either drive mirroring them or

synchronizing them to a cloud service).

6.5 Anonymity There is no guarantee of anonymity as a user of cryptocurrencies. This is because the schemes I have

presented have all transactions that have ever happened registered publicly. You can use a service like

Tor to hide your IP and thus cover up where the user is controlling his funds. However, it is important

to remember that everything in cryptocurrencies happen publicly, so most of your actions and

payments are still visible [13].

Because bitcoin wallets allow users to generate as many key pairs as they wish, it helps to make it more

unclear for observers which keys are connected to what wallet. Yet, research on the anonymity of

bitcoin users (which in the current context applies for the three I have mentioned) has shown that their

activities can be tracked [14]. Despite the users acting behind an IP proxy, they still track their money

transfers, find connected trade partners and even some times are able to reveal the identity of a user.

15

7 Conclusion My project task was to write about cryptocurrencies. I was to describe and compare existing schemes

for cryptocurrencies, describe the crypto mechanisms they were based on and finally discuss their

security and privacy aspects.

In this report, I have listed the basics of cryptocurrencies and how they work. I have also gone in depth

on the cryptology mechanics in particular, and explained how the cryptocurrencies use them. I listed

the three leading cryptocurrency schemes Bitcoin, Litecoin and Peercoin, and compared them. Finally,

I discussed the security and privacy aspects of the cryptocurrencies listed, and pointed out some

important factors.

During the project I examined how complex and complicated the cryptocurrency networks can be.

Considering the number of different types of schemes, one can potentially find a suitable one for most

users interested in joining. The most interesting factor when examining the leading schemes was that

only the ones that had their own distinct features were the most popular. Everything ranging from

early starts in the market, to fairness in mining to environmentally friendly options and more are

available.

Despite their basis on cryptology principles and open awareness of use, cryptocurrencies still have a

number of vulnerable factors. While Peercoin focuses on long-term operating principles, it still tries to

solve problems that are not necessarily going to be an issue. Collected mining power also serves as a

way for users to contribute to the respective system as well as giving them a chance to solve a hash,

yet the security problems with the mining pools remain a problem. In addition, cryptocurrency funds

are quite volatile and large investments in coins could become a great risk if not treated properly.

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8 References

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https://coinmarketcap.com/. [Accessed 14 April 2014].

[3] M. G. Olsen and A. Prinz, "http://grimstad.uia.no/dat300/," Universitetet i Agder, 2014.

[Online]. Available:

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March 2014].

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[Accessed 16 March 2014].

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[10] T. Worstall, "Forbes.com," Forbes, 12 March 2013. [Online]. Available:

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uses-15-millions-worth-of-electricity-every-day/. [Accessed 21 May 2014].

[11] "Wikipedia.org: Bitcoin," 2014. [Online]. Available: http://en.wikipedia.org/wiki/Bitcoin.

[Accessed 09 March 2014].

[12] "Bitcoinwiki.org: Weaknesses," 2014. [Online]. Available:

https://en.bitcoin.it/wiki/Weaknesses. [Accessed 19 April 2014].

[13] "Bitcoin.org," The Bitcoin Foundation, 2009-2014. [Online]. Available:

https://bitcoin.org/en/protect-your-privacy. [Accessed 8 April 2014].

[14] R. Fergal and H. Martin, "IEEE Explore," 2011. [Online]. Available:

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oin. [Accessed 19 March 2014].

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