**5. Performance discussion**

*Computer and Network Security*

as database) with the server.

**4. Covert channel with authentication leads to secure communication**

The proposed technique is responsible for creating secure communication channel using covert channel, encryption, and authentication. In the first step before using covert channel, the client and server must agree on pre-agreement table as shown in **Figure 4**, where it depicts out the pre-agreement table consisting of original key (OK) and its corresponding fake keys. The key point here is that the fake key is used in communication channel and the original key is kept secret in both sides (client and server). **Figure 5** illustrates the proposed technique, where the network consists of the client and server. The client agrees on shared information (e.g., table

The client wants to send to the server a message. Then, he encrypts the message using the original key. After that the encrypted message is attached with the fake key to be a parameter to HMAC function. HMAC depends on shared key between the client and server. Then the client sends (HMAC + encrypted message + fake key) to the server. Where, HMAC is used for integrity and fake key for server to know the

*Technique for transferring secure data through covert channel using covert channel, encryption, and* 

**114**

**Figure 5.**

*authentication.*

The implementation of technique is done by: first create a network as client and server with implemented java application. Client and server machines are 32 bit ×86, CPU Core (TM) i5 2.40 GHz, and Ram 4GB. Advanced Encryption Standard (AES) [26] algorithm is used in the implementation. Hashed message authentication code (HMAC) is used to guarantee the integrity [7, 11, 12]. The following issues are satisfying in this technique:


**Figure 6.** *The technique can handle multiple users in acceptable time.*

The time that is needed by the server to serve the client is measured. The technique can handle several clients with acceptable time as shown in **Figure 6**. The server needs less than 0.25 s to deal and handle 30 clients.
