# Efficient Key Exchange Using Identity-Based Encryption in Multipath TCP Environment
## 3 Related Work: Identity-Based Encryption (IBE) and Elliptic Curve Cryptosystem (ECC)  
The [PERSON] and [PERSON] [25] referred the IBE algorithm proposed by [PERSON] to drop the use of certificate authority (CA) for email application. Assume that the sender [PERSON] sends an email to \"[PERSON]AIL_ADDRESS]\" by encrypting the message using the public key \"[PERSON]AIL_ADDRESS]\" and sending it to [PERSON]. After receiving the encrypted mail from [PERSON], [PERSON] requests a private key generator (PKG) for the private key through authentication and decrypts the mail. The private key will be delivered to [PERSON] in his mailbox. In this way, one can share encrypted mail without setting up a public key infrastructure. The whole scenario [42] is as shown in Figure 9.  
By using similar concepts, the session keys that are being exchanged during the initial handshake in MPTCP can be encrypted by using IBE. Here, the Internet Protocol (IP) address of the host can be used as a public parameter, and the corresponding private key can be retrieved from the PKG. Instead of delivering the private key to the mailbox, the private key will be handed over to the receiver by authenticating the receiver by using its IP address and port combination, which offers the service/receiving service. The communication between the hosts and PKG is secured using the ECC. The security level offered by ECC is similar to the use of a smaller key size as compared to RSA [31; 43]. \begin{table}
\begin{tabular}{c c c c} \hline
**References** & **Year** & **Solution** & **Remarks** \\ \hline
[20] & 2011 & Hash chain-based solution & It does not offer security against on-path active attackers. \\ \hline
[19] & 2014 & Tcpcrypt & It does not authenticate the public key and is vulnerable to man-in-the middle attacks. \\ \hline
[18] & 2016 & Multipath Transport Layer Security (MPTLS) & Computation overhead during initial handshake. Need to modify the packet sequence. \\ \hline
[24] & 2016 & Modified initial handshake & During initial handshake, the values of the points are communicated in a clear format, which can be used in the future to initiate time-shifted attack. \\ \hline
[21] & 2017 & Sum chain-based solution & Vulnerable to time-shifted attack. \\ \hline
[41] & 2017 & Data Scrambling technique for privacy & The proposed model only focuses on the eavesdropper on untrusted paths and does not work in a strict sense. Moreover, integrity of the data is not guaranteed. \\ \hline
[17] & 2018 & ADD\_ADDR2 & Vulnerable to time-shifted attack. \\ \hline
[22] & 2019 & Key exchange through SDN & Single point of failure. \\ \hline
[33] & 2020 & Secure connection Multipath TCP (SCMTCP) & For each new connection request, it generates the unique key for each option, which increases the computational overhead. \\ \hline
[23] & 2019 & Secure and lightweight connection establishment scheme & Increases the packet overhead every time, confirming the new address and does not offer security against an eavesdropper in the initial handshake. \\ \hline \end{tabular}
\end{table} 
Table 3: Existing security solutions for MPTCP. _Secure Communication between PKG and Communicating Hosts_  
In order to secure the communication between hosts and PKG for the exchange of public parameters and private keys for IBE, the ECC is used. The ECC [44,45] is based upon the elliptic curve \(E_{p}(a,b)\) over finite field \(GF(2^{m})\), which satisfies the below cubic equation. \[y^{2}=x^{3}+ax+b,\]  
where \(4a^{3}+27b^{2}\
eq 0,\ a,\ b,\ x,\ y\ \in GF(2^{m})\). Here, \(x\) and \(y\) are the variables, and \(a\)_and_\(b\) are the coefficients. The equation represents a non-singular elliptic curve, where \(x^{3}+ax+b=0\) has three distinct roots. On the basis of the selection of \(a\) and \(b\), the shape of the curve may vary. The ECC can be defined using the Discrete Logarithmic Problem (ECDLP) and the Diffie Hellman Problem (ECDHP). ECDHP is a key agreement protocol, which works upon the concept of Diffie Hellman over elliptic curves. ECDLP is an extended version of DLP over a finite field.