Smart phones have become an essential part in the life of the individuals and their priorities at the present time. The most prominent uses are in chatting and conversation applications. Most of these applications do not provide the required protection and privacy of the data exchanged between users. Yet there are very few mobile chat applications that provides an End-to-End (E2E) security and privacy-preserving service to their clients. In this paper, a secure chatting application with end to end encryption for smart phones that use the android OS has been proposed. The proposed application uses the ECDH algorithm to generate the key pair and exchange to produce the shared key that will be used for the encryption of data by symmetric algorithms. The proposed Application allows the users to communicate via text messages, voice messages, as well as exchange photos. For the text message security the standard AES algorithm with a 128 bit key is used. The generated key (160 bit) minimized to 128 bit length in order to be used by the AES algorithm. For the voice and image security processes the proposed application uses the symmetric algorithm RC4 for this purpose. RC4 provides less security than AES, but it performs faster and this is required for such types and sizes of data.

RC4 algorithm is one of the most significant stream and symmetric cryptographic algorithms, it is simple and used in various commercial products, it has many weaknesses such as a bias in the key stream that some key bytes are biased toward some values. In this paper, a new algorithm is proposed by using initial state factorial to solve the correlation issue between public known outputs of the internal state by using an additional state table with the same length as that of the state to contain the factorial of initial state elements. The analysis of RC4 and developed RC4 algorithm is done based on their single bias and double byte bias and shows that many keystream output bytes of RC4 are produced key stream bytes that are biased to many linear combinations while developed RC4 key bytes have no single and double biases. The results show that the series that is generated by developed RC4 is more random than that generated by RC4 and the developed algorithm is faster than RC4 execution time and requires less time. Additionally, the developed algorithm is robust against many attacks such as distinguishing attack.