# A Survey of Public Key Infrastructure-Based Security for Mobile Communication Systems
## 3 A Survey of the Literature
### Review of PKI-Based Security for 3 GPP Systems  
The standard for the 3 GPP is evolving the system architecture evolution SAE-LTE architecture for the next generation of mobile communication systems. The SAE/LTE architecture provides secure service as well as 3G wireless local area network (3G-WLAN) interworking [26]. In order to provide secure 3G-WLAN interworking in the SAE/LTE architecture, extensible authentication protocol-authentication and key agreement (EAP-AKA) is used. However, EAP-AKA has several vulnerabilities such as disclosure of user identity, man-in-the middle attacks, sequence number (SQN) synchronization, and additional bandwidth consumption. The next generation mobile communication system is being developed for secure and fast communication [27]. The SAE/LTE architecture that is being developed by 3 GPP provides more secure communication than UMTS [28; 29]. To provide mutual authentication between UE and MME through E-UTRAN, the SAE/LTE architecture reuses UMTS-AKA [27]. This AKA protocol is called EPS-AKA. It generates an intermediate key, K-ASME, which can generate 5 keys for protecting transmission between the 3 GPP entities [28]. In this section, we present a brief review of the previous works done in the field of AKA for 3 GPP networks. [PERSON] et al. [30] proposed a mutual authentication scheme based on secure hash algorithm (SHA) for LTE using hyper elliptic curve cryptography, which is a PKC and helps in secure communication for data exchange. This mutual authentication scheme reduces communication complexity and computation cost by using smaller key sizes, which result in less processing time and also provide security against DoS attacks. Moreover, this scheme offers major advantages over traditional ones such as increased speed, less memory and smaller key sizes with higher level of security. [PERSON] and [PERSON] [31] in 2006 proposed an authentication scheme based on PKI for mobile systems (UMTS systems) to solve IMSI issues such as IMSI catcher, and man-in-the-middle (MITM)attack, and provide mutual authentication, integrity, and non-repudiation security requirements. Moreover, in this scheme the IMSI identifier is encrypted on the air interface and use the SQN as a random numbers to protect the users against replay and MITM attacks. However, we clearly can observe that the SQN is used in UMTS for a communication purpose in the particular of multiplexing and multiple access techniques e.g., CDMA as well as in data scrambling technique. Building on that and compared with [21; 24] this scheme consider to be impractical with low reliability due to its lack of security parameters functionalities. On the other hand, [PERSON] et al. [32] studied on the threats and attacks in 3G-WLAN interworking proposed a new AKA protocol based on EAP-AKA, which combines elliptic curve Diffie-Hellman (ECDH) with symmetric key cryptosystem. Furthermore, the proposed protocol provides perfect forward secrecy (PFS), mutual authentication, and resistance to replay attack. Additionally, compared with many previous protocols, which use PKI cryptosystem with certificates, this scheme reduces computational overhead. This is because it does not make SQN synchronization and does not consume bandwidth between the authentication authorization and accounting (AAA) server and the home subscriber server (HSS). Meanwhile, it still has a high computational cost due to the combination of ECDH with symmetric cryptosystems. [PERSON] et al. [33] proposed techniques for the existing problems that are related to AKA. This include compromising authentication vector attacks as they appear in current 2/2.5G/3G mobile communication systems, the study also proposed a scheme that combined secure sockets layer (SSL) with PKI elements and protects user's identity IMSI. This scheme assumed authentication as a service as to be performed at the higher protocol layers regardless of the basic network technology. Furthermore, the performance measurements are calculated based on \"prototype\" implementation for handshaking protocols.