# Efficient Key Exchange Using Identity-Based Encryption in Multipath TCP Environment
are adopting MPTCP for performance improvement in terms of bandwidth and fault tolerance by combining the usage of multiple network interfaces in mobile devices as well as in servers, datacenters, and end machines [7; 8; 9; 10; 11]. In order to facilitate the people of rural areas by providing access to various facilities using high-speed internet, Tessares has deployed MPTCP proxies to support hybrid access networks in different networks [12]. Smartphone companies such as Samsung, Huawei, LG, etc., have adopted MPTCP in their android devices to allow for the usage of multiple network interfaces such as Wi-Fi and long-term evolution (LTE) simultaneously to offer high-speed internet connectivity. By looking toward, the benefits of MPTCP in terms of higher throughput and fault tolerance at the time of Wi-Fi/Mobile network handover, Apple has adopted MPTCP for Apple Maps and Apple Music along with Siri since 2013 [8]. MPTCP also solves the issues related to reliability with high speed and robustness in vehicular IoT systems [13]. One of the important use cases of MPTCP is load management in data centers through multiple disjoint paths. Many architectures have been proposed for data centers, which differ from traditional systems in terms of link organization, but in all the architectures, servers are connected through multiple disjoint paths [14]. MPTCP can also be integrated with software-defined networks (SDNs) [15] to support optimized communication among governmental and commercial satellite communication systems and mobile unmanned aerial vehicle (UAV) heterogeneous networks [16]. MPTCP [17], an initiative of the Internet Engineering Task Force (IETF), is developed to offer efficient utilization of network resources, fault tolerance, and backward compatibility, which attracts various industries and academia to offer solutions in areas such as  
Figure 1: MPTCP and TCP connection. mobile communication, vehicular networks, datacenter networks, robotics communication, software-defined networks, etc. MPTCP supports the multi-homing and multi-addressed nature of hosts for data transmission, which opens the door for security threats while availing the higher bandwidth and fault-tolerance that encourage many researchers to study the security issues of MPTCP and its solutions. MPTCP uses the TCP header to incur a positive impact on the traditional TCP aware applications to achieve the goal of backward compatibility by using various options in TCP headers such as MP_CAPABLE, MP_JOIN, ADD_ADDR, etc., but they are vulnerable to attacks other than TCP. The ADD_ADDR option can be used to initiate a session hijacking attack by a man-in-the-middle attack, MP_JOIN can be exploited to initiate SYN flooding attacks and denial of service (DoS) attacks. Moreover, the key exchange in plaintext during the initial handshake in MPTCP invites other security threats because these keys are used for subflow authentication in the future. The focus of this article is on the security of MPTCP against ADD_ADDR vulnerability and security of keys exchanged during the initial handshake, which can be used to initiate various attacks. Many solutions such as Transport Layer Security (TLS) [18], tcpcrypt [19], hash chained [20] and sum hash chained-based encryption [21], key exchange using SDN [22], secure and light-weight solutions [23] have been proposed and implemented by researchers to provide security against various attacks such as session hijacking, DoS attack, SYN flooding, etc., but some solutions increase overhead, which decreases overall performance of MPTCP, and in some solutions, the doors are still open for the attackers, which are available during initial key exchange. The attacker present during the initial handshake can obtain the key to initiate various attacks by bypassing the authentication at the time of adding a new subflow, advertisement of a new address, changing the priority of subflow, etc.