Research And Implementation Of Secure Communication System For OMA Lightweight Machine-to-Machine

As the main standardization organization of mobile services,open mobile alliance OMA puts forward the communication standard for the constrained-node networks of Internet of things,that is,lightweight machine to machine LWM2M.It adopts the CoAP protocol proposed by IETF core working group,and defines the protocol stack of CoAP over SMS to ensure the communication requirements of the constrained-node networks.The CoAP over SMS based on Californium open source framework studied in this paper can meet the communication requirements of the constrained-node networks.But there are still some problems in the network communication environment:The first is the lack of communication reuse capability between an application server and multiple restricted nodes;The second is the problem of DTLS1.2 in the communication environment of CAP over SMS,that is,the limitation of MTU using SMS makes the transmission of cookie carrying handshake message ClientHello error,and there is no corresponding response method in DTLS 1.2 standard text;The third problem is the integration of existing Internet applications and the constrained-node networks,that is,IP address is required in CoAP and DTLS 1.2,but there is no IP address in SMS,and this problem has not been properly considered in OMA and IETF CoRE working groups,which has become one of the important problems restricting CoAP over SMS applications.In order to solve the problem of CoAP over SMS,this paper proposes a secure communication system for OMA LWM2M based on the protocol stack of CoAP over SMS in Californium open source framework:Firstly,the UDP protocol is introduced into the CoAP/SMS protocol stack to form the CoAP/UDP/SMS protocol stack,and the UDP port number is used to realize the multiplexing ability of the application service using CoAP over SMS when managing multiple nodes;CoAP message is encapsulated in UDP datagram,and SMS message is used to deliver UDP datagram,so as to realize the reuse ability of CoAP over SMS application server.Using UDP port number to reuse application server is the standard method of Internet.Secondly,improve the fragmentation and reorganization mechanism of DTLS1.2 handshake messages to ensure the correct application of DTLS1.2 in COAP over SMS,that is,the availability of CoAP/DTLS/UDP/SMS in LWM2M environment.The length limit of SMS 140 bytes will be exceeded when ClientHello is encapsulated on UDP after carrying cookie.However,DTLS1.2 does not propose relevant solutions when the length of ClientHello is too long and exceeds the lower MTU limit.The solution proposed in this paper is to determine the size of the ClientHello message when it is sent.If it exceeds the set MTU,it will be transmitted in pieces;When the ClientHello message is accepted,it is judged whether it has been partitioned,so as to decide whether to cache it and reorganize it.This work is also a supplement and improvement to DTLS1.2 standard.Thirdly,a mapping method between SMS sender/receiver number and IPv6 address is defined.According to the format and length of international mobile phone number,SMS number is mapped to IPv6 unicast address within the specified range.Logically,it makes SMS number a specific IPv6 address to provide a form of IPv6 address in CoAP over SMS protocol stack,so as to support the communication integration between existing Internet applications and SMS based the constrained-node network.This paper designs and implements CoAP/UDP over SMS and CoAP/DTLS/UDP over SMS.In the system experiment,both of them can run in real Android environment.Among them,the server based on SMS has the ability of reuse,and can interact in the DTLS security environment,which supports the integration of the existing network and the limited network based on SMS.This paper presents a secure communication system for OMA LWM2M.