This document proposes a decentralized instant messaging system for the Internet of Things based on blockchain technology. It analyzes problems with centralized instant messaging systems, including potential information leaks and identity forgery. The system would use a peer-to-peer network without a central server, separating nodes into full nodes that store all blockchain data and light nodes that process messages without storing the full blockchain. This model is analyzed as a secure and reliable way to enable communication and data transmission between growing numbers of Internet of Things devices.

1. A Decentralized Instant Messaging System
of Internet of Things Base on Block Chain
Technology
ABSTRACT
Bitcoin block chain technology architecture is emerging based on
decentralized technology, which is the main innovation of Bitcoin.
There are lots of applications based on block chain technology, such
as Bitcoin, Bitshares and IBM ADEPT systems in the Internet Finance
field. But there is not too many application and literature related to
the block chain on the Internet of Things. Applying the block chain
technology of decentralization on the Internet of Things, which could
work without a centralized server. It has many advantages, such as
high security, anti-counterfeiting, peer nodes, and undeniably digital
signatures.
There are lots of problems with the Internet of Things and instant
messaging system:
1. There are more and more nodes with the development of the
Internet of Things. We need to build a safe, reliable connection and
communication between the nodes and have good robustness and anti-
aggressive.
2. Traditional instant messaging system has the problem of
centralized server architecture, information storage, transmission
possibly leaking, identity forgery and so on.
This paper focuses on two aspects of these problems. The main work
is summarized as follows:
1. Analyzed the advantages and disadvantages of the traditional
star network of centralized network architecture. Proposed to create
a peer to peer network based on block chain technology. This network
has a multi-node communication system, which doesn't need a central

2. server of administration.
2. Block chain for networking applications in some of the smaller
equipment storage space, this paper proposed the concept of full nodes
and light nodes. Full nodes store all the messages of blocks, and the
light nodes processing the message without store the block chain, which
could meet the growing demand of memory storage. Full nodes include
complete block chain, generate a new block of block chain, receive the
information which is light nodes sending, receiving and forwarding
information. Light nodes have a complete business process logic
functions, but only have a network of reception, as well as a small
amount of computing power and storage space for things some have low
storage capacity and computing device application scenarios.
3. In response to the industry's expectations of Internet of Things
based on the block chain technology. This paper proposed a complete
model based on block chain, and an instant messaging system is built
based on this model. And the system is simulated and verified.
4. To solve the problem of the real-time communication, information
leaking in storage and how to establish a proper trust model and other
issues in peer P2P networks ,the tile-based chain of IOT model
established by this article, is a credible peer P2P network trust model,
to achieve a safe and reliable public key encryption algorithm
asymmetric exchange mechanism. Block chain by way of open public key
technology node and the node name and bind, thus ensuring the data
during transmission and storage confidentiality, as well as the message
sender's repudiation of its signature.
This paper is divided into five chapters: Chapter 1 described the
research background, methods and content; the second chapter analyzed
the main features and technical architecture bitcoin block chain
technology; the third chapter designed the architecture of the Internet
of Things based on block chain; Chapter 4 designed and validated a
decentralized instant messaging system, based on the application of
the Internet of Things of block chain. And Chapter 5 draw the
conclusions and outlook, and summarized the advantages and
disadvantages of the block chain technology.

3. Keywords Bitcoin， Block chain， Decentralization， the Internet
of Things， Instant messaging