design knowledge management processes to measure
interactions between humans and connected objects
in order to evaluate the relationships between these
two types of actors. The objective is to provide clear
information about what these actors can do and for
which purposes. To do this, we can model the power
of action of these actors (Brun, 2017) to analyze how
their interactions in a given situation and for a spe-
cific purpose, increases or decreases their power to
act. Our hypothesis is that dynamic and interactive
representations of this power to act are a way to bet-
ter understand the capabilities of IoT devices: what
are the offered services? Which difficulties can be
encountered? What are the relationships between dif-
ferent objects? The main issue then becomes a ques-
tion of knowledge design: how to manage the inter-
actions between the knowledge of users and those of
connected objects in a digital environment?
Alongside these knowledge management issues,
the centralized architecture of IoT platforms raises
many issues in terms of security and privacy pro-
tection. Due to its decentralized and distributed na-
ture, Blockchain technology seems to address these
issues (De Filippi, 2018). However, the character-
istics of the IoT devices, for example their limited
computing power, do not facilitate this adaptation.
Similarly,understanding the complex mechanisms in-
volved in the Blockchain makes this technology diffi-
cult to master for non-specialist users.
To illustrate and clarify how to conceive a secured
knowledge design that respects users’ privacy in the
context of smart devices, we will begin by examining
the Blockchain and its related technologies. In partic-
ular, we will focus on ”smart contracts” which give
us a glimpse on a new way of contracting without a
need for a trusted third party. In a second step, we
will describe how to use the Blockchain in the IoT
through the example of a dynamic and interactive de-
vice for collectively analyzing activities related to a
connected refrigerator. Finally, we will discuss the
advantages and drawbacks of this type of system.
2 WHAT IS THE Blockchain
In 2008, Satoshi Nakamoto (pseudonym) published
a paper on Bitcoin (Nakamoto, 2008). In this arti-
cle, the author describes a new cryptocurrency called
Bitcoin. The latter is based on a technology called
Blockchain. It is a public distributed and decentral-
ized ledger in which transactions are recorded across
multiple nodes of a peer-to-peer (P2P) network. The
Blockchain is attack resistant, ubiquitous, verifiable
and auditable.
To transfer virtual currency, Blockchain users,
who are identified by their public keys,generate and
broadcast transactions on the network. These transac-
tions are grouped into blocks by users. When a block
is filled, it is added to the Blockchain after a ”mining”
process. To mine a block, nodes of the network, called
”miners”, try to solve a cryptographic puzzle called
”Proof-of-Work” (PoW). Once the block is validated,
it is time stamped and added to the Blockchain. The
transaction is then visible to the receiver as well as to
the entire network (Saleh et al., 2018).
Since the invention of Bitcoin, other consensus
mechanisms beside PoW have emerged. For exam-
ple, we can talk about Proof-of-Stake (PoS) or Proof-
of-Importance (PoI). In the first one, users who have
more coins have the responsibility of validating trans-
actions and protecting the system because they are
the ones who invested the most in it and are there-
fore the most concerned about its good performance.
Proof-of-Importance was introduced by NEM (Cap-
stone, 2015). In this consensus mechanism, a rep-
utation system is built for the network, based on an
importance value associated with each account. The
higher this value is, the greater the chance of being
chosen to create the next block.
Based on the work of (Febin, 2018) (Sher-
min, 2017), we can distinguish three main types of
Blockchain :
• Public Blockchain: as its name suggests, it is a
large public ledger. No entity is in charge and
all nodes of the network can read data from the
Blockchain, participate in transaction validations
and auditing. Having a computer with an inter-
net connection in enough to become a node of
the network and get a complete history of the
Blockchain. The advantages of this system are
transparency and anonymity, since each node is
only identified by its public key. In addition, the
redundancy of the public Blockchain and its repli-
cation over the network makes it very secure and
immutable. However, transaction validations are
slow and require significant computation power.
This type of Blockchain is mainly used for cryp-
tocurrencies such as Bitcoin or Ethereum.
• Private Blockchain: It is a kind of restricted
Blockchain. It is under the management of an
authority that oversees the creation, verification
and validation of each transaction. The data is
not open to the public and permissions are re-
quired to access it. Because of their nature, pri-
vate Blockchains do not provide decentralized se-
curity, but offer increased efficiency for checking
and validating transactions. Their use is destined
for public or private companies.
IoTBDS 2019 - 4th International Conference on Internet of Things, Big Data and Security
400