Abstract:By employing the characteristics of the basic structure (keystream), Stream ciphers designers attempt to create algorithms that have advanced features from security and speed point of view. They take into consideration the state-of-the-art scientific and technical developments to design more advanced algorithm versions. This research proposes the design of a new efficient and secure stream cipher, named BloStream which proves to be more secure than conventional stream ciphers that commonly implement Exclusive-OR (XOR) for mixing. The proposed algorithm encompasses two major components. The first part involves the Pseudo Random Number Generator (PRNG), exhausting Rabbit algorithm. And the second part involves a nonlinear invertible round function (combiner), depending on Rijndael-like function algorithm, to perform the encryption/decryption processes. This new construction strengthens the weak XOR combiner. The proposed cipher is not only a random number generator but also a self-synchronizing stream cipher in such a way that the cipher text influences its internal functioning. The proposed algorithm utilizes 16-bytes secret key to encrypt the plaintext which is a multiple of 16-bytes up to 2 64 bytes length. The evaluation of BloStream performance, in terms of implementation aspects and security properties as well as the statistical test for keystream and comparison with similar systems revealed that, BloStream was more efficient, faster, and securer than the conventional stream ciphers.Key words: Stream ciphers, rabbit cipher, Rijndael-like function, combiner algorithm, PRNG. IntroductionStream ciphers are an important class of symmetric encryption algorithms. They encrypt individual characters or binary digits of a plaintext message one at a time, using an encryption transformation which varies with time. They are also more appropriate, and in some cases mandatory (e.g. in some telecommunications applications), when buffering is limited or when characters must be individually Ring the plaintext with a random key. The drawback of the Vernam cipher is that the keystream must possess a true random sequence, shared by the sender and the receiver, and it can only be used once [1]-[3]. A combiner is the heart of a stream cipher, which generally employs an 'additive' combiner such as XOR. Additive combiners have absolutely no strength at all; this means that, if an opponent somehow comes up International Journal of Applied Physics and Mathematics 153Volume 5, Number 3, July 2015 An alternate approach to the design of a secure stream ciphers is to seek combining functions which can resist attack; such functions would act to conceal the pseudo-random sequence from analysis. Such cryptographic combining functions could be utilized to substitute the Vernam XOR combiner provided that they have an inverse. An improved combiner is intended to enhance the sophistication of cryptanalysis, making it more time consuming and expensive than simple combiners [6]. Dynamic substitution is a way to build a cryptographic comb...