# A Survey of Public Key Infrastructure-Based Security for Mobile Communication Systems
## 3 A Survey of the Literature
### Review of Symmetric-Key Based Security for Mobile Systems  
Symmetric cryptography (single key cryptography) was the only type of encryption in use before public-key cryptography in 1976. The main idea is to use the same key for encrypt/decrypt or sign/verify unlike PKI cryptosystems which are used different keys. However most of the old security techniques for mobile communication systems based on symmetric cryptosystems due to its low computational cost and communication overhead, but it has low security level than PKI systems. Meanwhile, mobile systems have rapidly developed as well as the PKI techniques which became more flexible and suitable for the recent mobile systems. In 2009 [PERSON] et al. [46] proposed an efficient authentication scheme with anonymity for global mobility networks (GLOMONET) that uses low-cost functions such as one-way hash functions and exclusive-OR operations. It provides a relatively low computational cost and good resistance against possible attacks such as known-key, forgery, and replay attacks. However, the proposed scheme consists of three phases and three rounds handshaking processes between three entities. Thus, we can note that the proposed scheme has a relatively high exchange processes which is impractical with mobile systems especially in case of roaming. Moreover, the session key is controlled by the mobile user regarding his home agent without including all entities contributions, hence [PERSON]'s scheme provide unfair key agreement, besides that the scheme provide no mutual authentication or end-to-end security. In 2010 [PERSON] et al. [47] proposed a secure and lightweight authentication scheme with user anonymity for wireless communications. This scheme based on symmetric cryptography, hence it provides a relatively low computational cost. In addition, it requires four message exchanges between mobile user, foreign agent and home agent. The proposed scheme provide session key only between the mobile user and the visited network. In addition, this scheme claimed to provide a smart card security technique only if user password for the smart card remained secure. However, the scheme based on ECC cryptosystems and it used SHA-1 hash function in the authentication phase in total of five phases between four entities and that makes the proposed scheme unsuitable with the mobile systems beside it requires a certificate authority with high handshaking processes cost and does not provide mutual authentication or end-to-end security. In general, [PERSON]'s scheme [47] is not flexible with the requirements of wireless systems. [PERSON] and [PERSON] [48] proposed a lightweight mutual authentication and key agreement scheme for GLOMONET providing user anonymity. This scheme tried to correct some of the previous proposed techniques by simplify the scheme especially when we are dealing with lightweight mobile systems. The proposed protocol consists of three phases, and also consists of three entities. However, the proposed scheme lacks of end-to-end security and vulnerable to many kind of attacks. Therefore, in 2016 [PERSON] and [PERSON] [49] tried to improve their previous scheme and proposed an efficient mutual authentication and key agreement protocol (MAKA) to protect the data flow against interception as well as provide a key agreement technique based on session key. The proposed protocol also consists of three phases: registration, MAKA, and password renewal phase, and consists of three entities: mobile user, foreign agent, and home agent. Though Prosanta's scheme [49] is considered to be a highly secure, provides a relatively low computational cost, and achieves the security requirements, but it still lacks end-to-end security properties even the mobile user can change his/her password without any help from other entities; hence end-to-end security issue is considered as the new challenge for mobile networks today.