Abstract-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.

RC4 stream cipher is an encryption algorithm that is used in two domains of security realized for IEEE 802.11 LANs: one of them is wired equivalent confidentiality and the other is WI-FI Protected Access protocol. It is symmetric encryption, fast, and simple algorithm. It has different weaknesses such as the bias that occurs in the key stream bytes. Key scheduling phase is more intricate. It was prepared to be unnecessarily easy. The initial few bytes of keystream that are generated by pseudo random generation algorithm (PRGA) are biased to several bytes of the private key. Thus, the byte analysis makes it probable for attacking RC4 in some methods of operations. This paper presents a new stream cipher algorithm as a development for RC4, named double RC4 key generation, which is submitted to solve interconnection problems in the output of the inner state and solve the problem of weak keys. The new idea allows random access to the key stream. The keystream depends on all preceding state bytes. RC4 and the proposed algorithm are analyzed and proved that the new algorithm has no single or double byte bias in the key stream while RC4 has proved the same bias that is shown in the literature. The proposed algorithm introduces high resistance against different attacks that are applied to RC4 and the generated key stream has high randomness, large complexity, and good statistical properties.

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