ArticlePDF Available

What is Blockchain: a Gentle Introduction


Abstract and Figures

This paper presents a step by step introduction to what blockchain is and how it works.
Content may be subject to copyright.
Blockchain: Simple Explanation
Oleg Mazonka, 2016
Abstract—This paper presents a step by step introduction to
what blockchain is and how it works.
Index Terms—Blockchain, Hashchain, Bitcoin, Cryptocur-
Blockchain is a buzzword. You have probably heard it so
many times you feel like you should undersatand what it is.
By the end of reading this article you just might.
The original problem comes from the idea to have some-
thing represented as digital entity that can be passed securely
from one party to another. Imagine you have some money in
your bank account, and you would like to securely transfer
some of it to another person. This ususally goes through a
digital transaction – no physical money is passed around.
This is nice and simple. But, it requires trusting the bank.
Is it possible for some digital entity stored on my computer,
representing money, to be passed securely to someone’s else
computer, without a bank? Yes it is possible. However, re-
gardless of representation any digital sequence can be copied.
This creates the well-known problem of “double-spending”:
one person makes an electronic transaction more than once
using the same money. This problem was not solved properly
until the first blockchain cryptocurrency, Bitcoin, appeared in
Many other cryptocurrencies appeared in the following
years and followed the same principle of blockchain tech-
nology, which solves the double-spending problem without a
bank. The digital sequences, which are linked to a person, are
passed around without possibility to copy and double-spend
by placing one hashchain inside another hashchain. What is a
hashchain? Let us first recall what is hash.
Hash function is a method to convert data of arbitrary size
into a digital string of predefined fixed length, called hash.
One of the simplest hash functions is the modulo operation.
Any digital string can be converted into a number (possibly
very big); this number can be divided by a constant; and the
remainder of that division is the result, hash. Obviously the
result is less than the constant, because its size is no greater
than the size of the constant. This hash function is simple but
at the same time not used too often because people want to
have another property – one way computation. It should be
easy to compute the hash, but finding any input to the hash
function must be difficult, or better virtually impossible.
Hash functions with such a property are sometimes called
cryptographic hash functions, if necessary to distinguish from
others. Such functions digest the bits of the input data in
a very convoluted way to make the reversible computation
impossible. The best known cryptographic hash functions are
MD5, SHA1, SHA2. An example of MD5 is this
MD5(”abc”) = 900150983cd24fb0d6963f7d28e17f72
The result is a 128-bit string shown here in the hexadecimal
If the hash value, represented in some form, is fed again
into the hash function, a new hash is obtained. If this process
repeated and the results are combined into a sequence of
hashes, one obtains a hashchain.
Hashchain is a sequence homogeneous data chunks, or
simply blocks, linked together by a hash function. Figure 1
schematically shows a simple hashchain.
Figure 1
Each data block consists of the hash and the payload. The hash
of each block is calculated out of the whole previous block.
Payload in each block is arbitrary data. This hashchain has
the important property: no data can be modified at any block
without affecting the integrity of the subsequent blocks. For
example, if the payload of the first block is changed, then the
hash of the second block must be changed as well, and hence
the hash of the third, and so on.
Next step is to authorise only one person to create a
new block in the chain. One way to do it is Public Key
Cryptography (PKC).
The basic idea of PKC is similar to hash functions – one
way computation. Given some data m(mfor message) anyone
can compute encrypted value Enc(m). But, only the one who
knows a special key related to this encryption can compute in
the opposite way, i.e. find mfrom Enc(m). The latter process
is called decryption.
To achieve PKC, one must first create a so-called pair of
keys: public and private. The public key is used to encrypt
data and can let be known to anyone. The private key is used
to decrypt and must be kept in secret.
Figure 2 shows schematically the arrows of computation.
The top arrow represents the theoretical possibility to decrypt
without knowing the private key upfront. For example, RSA
encryption is based on mathematical property of big number
Figure 2
Public Key
Not possible but
theoretically imaginable
If someone finds a way to factorize a big number (which is the
public key), then that person would be able to decrypt without
knowing the private key, in fact breaking the cryptography.
There are two main scenarios where PKC works. The first
is when one party wants to send a secure message to another.
In this case the first party encrypts the message by the public
key of the second party. The encrypted message can be made
public because only the second party is able to read the
message encrypted with their key. The only vulnerability of
this method (apart from the theoretical one by cracking the
math) is knowing and trusting the public key in the first place.
To attack this problem a whole system of hierarchical public
certificates exists, for example, in the Internet https protocol.
The second scenario is quite opposite to the first. Given
some data, Alice encrypts it using its private key (or encrypts
only hash from the original data) and then publishes both data:
the original and encrypted. Anyone knowing the public key
can verify that encrypted data is actually computed using the
private key that is paired with the public key used for decryp-
tion. This verification works as a validation Alice actually did
that. That process is called digital signing and the encrypted
part is called digital signature.
Figure 2 shows the first scenario. In the second scenario the
private and public keys are swapped. Let us follow this again.
Alice takes a hash from a document mand encrypts this hash
using his private key, then makes both the document and the
encrypted hash public. Anyone else can take the hash of the
document and decrypt the encrypted hash using the public key
of Alice. If these two values are the same, then it means that
Alice has indeed signed the document m. This scenario with
digital signatures is the one which is useful in hashchains.
Now, let’s go back to the question of whether it is possible
that only one person is enabled to add a block to the hashchain.
If the last block (Figure 1) contains the public key of the
current owner and the digital signature of the previous block
owner, then creation of the next block will require the signature
of the current block, i.e. of the person who has the private key.
When creating a new block the current owner places another
public key in the next block and signs that block. So the
next block will be owned by whoever keeps the private key
corresponding to the newly published block. And the signature
proves that only the previous owner could have done that.
Figure 3 (from the original Bitcoin paper of Satoshi Nakamoto)
Figure 3 shows how PKC can be used in hashchains.
Hashchain with PKC authorisation can perform as a func-
tion for secure transfer of digital objects, called tokens.
Suppose that one hashchain represents a token. It may be
something to which the real world assigns a value. The owner
of the last block is the owner of this value because only he
is able to pass it to somebody else. However this kind of
hashchain implemented as-is would require a central place
where the blocks are actually created, stored, and can be
verified. We come back to the concept of a bank – a place
which is required to be trusted.
Imagine that there is a place (possibly in virtual reality)
where a continuous process exists that constantly creates new
blocks for some global hashchain. And imagine that you can
place any data you like into the payload of the blocks of that
global hashchain. If such a place and process would exist, then
you can insert the blocks of a hashchain representing values
into the blocks of this global hashchain. In other words that
would be one hashchain inside another hashchain. Essentially
this mechanism is called blockchain technology.
Figure 4
Hash Hash Hash
Figure 4 shows an external hashchain where block data
consists of blocks of internal hashchains. The blocks of the
internal hashchains can chaotically appear in the external
hashchain. The obvious condition is that older internal blocks
cannot appear in newer external blocks.
Different solutions exist on how to organise that global
hashchain. And one particular solution proposed in the original
Bitcoin paper made Bitcoin popular.
In Bitcoin network the global hashchain is a database dis-
tributed among many computers. This global hashchain con-
sists of many internal hashchains representing some valuable
tokens called bitcoins. New blocks created on those internal
hashchains are called transactions, because they represent
changing ownership of bitcoins. The owner of a particular
bitcoin creates a new block on the corresponding internal
hashchain and publishes this block as a new transaction to
be included into the next block of the external hashchain.
Publish means sending to all other known participants of P2P
Bitcoin network. When a new block of the external hashchain
is created it is published in the same way.
Any participant can create a new block for the external
hashchain including published transactions into the block. But
this is not easy. To avoid chaos all participants follow a
particular set of rules – the protocol. And whoever does not
play by these rules is ignored. The protocol is based on three
1) creating a new block requires significant computational
2) creating a new block is rewarding, so many would make
en effort to successfully create a new block, and
3) when branching occurs, the longest branch wins.
The first one simply requires that the hash taken from the block
plus some random data, starts with a number of zero bits. So
this random data is modified and the hash is calculated until
the condition of zero bits is achieved. That requirement makes
block creation difficult.
On the other hand whoever creates a block receives a num-
ber of newly created internal hashchains representing some
value, bitcoins. That also is part of the protocol. Moreover
since the bitcoins represent a kind of currency and internal
hashchains represent transactions with that currency, the trans-
action owners can give a small portion of the transaction value
(fees) to the creator of the new block of the global hashchain.
So the creator of the new block receives the newly created
bitcoins plus all fees collected from the transactions placed
into the block.
The third rule ensures that there is only one current valid
copy of the database distributed among many computers.
It is obvious that since many parties try to create blocks,
some different blocks are created independently. Since the
propagation is not instant, new blocks may be created on top
of those independently created blocks. That makes the global
hashchain branch. The third rule makes sure that only one
branch which is the longest is considered to be valid. This
rule works fine because block creation is difficult, hence the
probability of two or more branches surviving die out very
We can see that the external hashchain plays the role of
the central repository effectively replacing an authority entity.
Since the external hashchain is global, it stores bits and
pieces of internal hashchains uniquely and reliably binding
the tokens with their owners, at the same time making double-
spending impossible. The database of the external hashchain
is distributed among many not trusting each other parties, so
it makes it more difficult to enforce the whole community
of those parties to follow some externally applied regulations
such as political laws.
Blockchain is a particular organisation of hashchains inside
another hashchain. The external hashchain has to be based on
a set or rules that make balance between usability, simplicity,
incentive, and trust and authority. Its purpose is to replace
the central access point that can be controlled and possibly
abused by a human. Internal hashchains are required to have
authorisation mechanism so one party can own something
of particular value. The authorisation mechanism may not
necessarily be PKC. For example, Hasq hashchain is a much
simpler hashchain using only hash functions as authorisation.
... If the last block contains a public key of the current owner and the digital signature of the previous block owner, then next block creation will need a signature of the current block of the person who has the private key [7]. When creating new block current owner should place a new public key in the block and need to sign it with the private key. ...
E-commerce is the more reputed way to do transactions nowadays and all the online transaction use multicurrency. At present, e-commerce and online trade is the most popular way to buy or sell anything and this domain has become a very broad and wide area. These e-commerce and online trading applications are using a different level of security mechanism and those mechanisms provide some certain level of security. These security mechanisms basically depend on third-party authentications using symmetric or asymmetric key cryptography approaches. Most of the online trading applications use SSL (Secure Sockets Layer) mechanism to implement the secure connection between server and client. Anyway, all the existing security mechanisms have to use a third party to ensure their secure information and connectivity. When using any third party or middle hand to authenticate any transaction still there can be a lot of vulnerabilities since security control and sensitive data been shared with an external party. As a solution to this situation block-chain concept was introduced and using this concept, third-party dependencies of an application can be eliminated. Since blockchain concept working as a common ledger for all the users' access to the peer-to-peer network no need to validate information against external third party and also no one can update without knowing others in the network. Most of the existing online trading application and payment systems have been integrated with the actual bank and all these bank transactions are always use bank profiles to do any transaction. But using cryptocurrency like bitcoin no need to have a bank profile and it is very fast compared to others. Currently, all the other fiat-currencies has a tendency to inflate and it can be very time dependent but it's very important to find out noninflationary currency that will be helpful for the stability of the economy. This solution mainly based on the bitcoin which is well-organized crypto-currency and peer-to-peer payment method and it has more value-added features than existing wallet services and peer-to-peer payment applications. This application basically focuses on the high-security wallet mechanism, wallet restore functionality in any crash or vulnerability 3 situation and also user-friendly application to the user with seamless transaction delay time. And also this application is open source user creation and any user can create a wallet with basic validations and can use for any bitcoin transfer functionalities. Using this application user can always check his balances and transaction history at any time and also this APIs can be integrated with any front-end client since back-end service have been implemented as micro-services endpoints. As an end product, this will be an open source high secure bitcoin wallet application with integration capability with any third party services like a bank, card applications.
The analysis of latest tendencies in the market of information systems, shows two primary technologies which has high impact on industry. They are: cloud services and blockchain technologies. Both technologies are vivid for the business and found their application in the ERP systems. Development and use of ERP in cloud is not an innovative idea, as the number of cloud ERP solution exists currently, but blockchain technology use for ERP in the cloud gives additional benefits from difference points of view. As mentioned in Mearian, L. (2018), one of the potential benefits of blockchain for cloud ERP is related with changing private ERP systems of single company to the collaborative platform among partners and external users of the business entities. This tendency is especially highlighted in the field of supply chain management (SCM) and there are several publications, which discusses this issue and propose possible solution, as example Korpela, Kari & Hallikas, Jukka & Dahlberg, Tomi. (2017) deals with transformation of digital supply chain using blockchain technology; Banerjee, Arnab. (2018) makes the technical feasibility study on the mentioned issues. But development of the more open cloud ERP systems leads always to the security issues. Here the blockchain could be the possible solution, as it could create not only collaborative platform based on cloud ERP, but also provide the security mechanisms. As example Westerkamp, Martin & Victor, Friedhelm & Küpper, Axel. (2018) discusses the traceability of the transaction in supply chain management system and underlines the technical feasibility of the blockchain based solution. The analysis of the literature shows that question regarding cloud ERP and blockchain integration is still open for discussion and additional research in this area is expected. The aim of the current research is to provide the set of recommendation on blockchain technology application for cloud ERP. The study was conducted, by applying SWOT analysis and GAP analysis using the IS-AS technique. Explaining the potentiality of this migration of business into Cloud ERP by using Blockchain Technology to overcome the client security issues and making this transparency. This study underlines the security recommendations and how latest technology like Blockchain will fill this gap with this technology.
ResearchGate has not been able to resolve any references for this publication.