**Abstract**

The keys which are generated by cryptography algorithms have still been compromised by attackers. So, they extra efforts to enhance security, time consumption and communication overheads. Encryption can achieve confidentiality but cannot achieve integrity. Authentication is needed beside encryption technique to achieve integrity. The client can send data indirectly to the server through a covert channel. The covert channel needs pre-shared information between parties before using the channel. The main challenges of covert channel are security of pre-agreement information and detectability. In this chapter, merging between encryption, authentication, and covert channel leads to a new covert channel satisfying integrity and confidentiality of sending data. This channel is used for secure communication that enables parties to agree on keys that are used for future communication.

**Keywords:** encryption, authentication, dynamically, covert channel, confidentiality, algorithm, undetectability, fake key

## **1. Introduction**

Encryption is considered the main key factor of security to achieve confidentiality and to protect data from disclosure [1]. Encryption is not efficient to achieve integrity. It needs another factor called authentication [2]. Covert channel is created to transfer data indirectly between client and server; it was created by Lampson [3].

Before the client and server use the covert channel, they must agree on a preagreement knowledge. Also, they agree on how to send that knowledge. A good example is they agree on even word meaning "00" and odd word meaning "11." If the client sends "communication channels," the server will know that the client's message is "1100" [4, 5].

Covert channel cannot be detected if the following two factors exist: plausibility and bit distribution. Plausibility deceives the attacker who thinks that the channel is normal channel and it is not used to send secret information. On the other hand, the bit distribution of normal channel must same distribution of covert channel [5].

The technique is worked as shown in **Figure 1**, where it shows the general idea of the proposed technique. Covert channel needs shared information. In my protocol, it is considered as a table shared between the client and server. This table contains characteristics of the client such as the name which represents the original key. Each

**Figure 1.**

*Secure communication using covert channel, encryption, and authentication.*

original key has fake keys. I used encryption algorithm to guarantee the confidentiality. HMAC is used to check integrity. Finally, the time that is needed for the client and server to agree on secret information (e.g., secret keys) is measured.

In this chapter, secure communication channel for transferring data is implemented. The channel between the client and server is considered a covert channel that depends on authentication and encryption.
