### Symmetric Stream Cipher Based On Chebyshev Polynomial

D. Sravana Kumar
2017 International Journal Of Engineering And Computer Science
The rapid development of information technology turned internet as the basic means and wide choice for communications. Due to extensive adoption of internet for communications it is essential these days to conceal the message from unintended reader. The present paper describes a new encryption algorithm using Chebyshev polynomial of I kind. The plain text is encrypted in three rounds each round consisting of two stages with the concatenation of the previous cipher character with different keys.
more » ... For making the algorithm more secure the key for the first round of encryption is generated from the main key (agreed upon by the sender and the receiver) and the subsequent round keys are concatenated with the previous round keys. The stream cipher proposed here has several advantages over conventional cryptosystems. Introduction: Secure transmission of the sensitive information to the intended recipient with confidentiality is the essence of cryptography. Message encryption is one way of achieving the confidentiality [10]. Performing modular arithmetic operations and bit-wise logical XOR operations repeatedly strengthens of the cipher [4]. But simple XOR encryption is vulnerable to several types of active and passive attacks. Performing logical XOR operation along with the concatenation with the previous round cipher enhances the security levels. Concatenation: String concatenation is an operation used in computer programming and data base theory. In conventional T 4 (x) = 8x 4 -8x 2 +1 T 5 (x) =16x 5 -20x 3 +5x T 6 (x) =32x 6 -48x 4 +18 x 2 -1 First few Chebyshev polynomials of I kind are shown in the following graph Earlier work on Chebyshev Polynomial: Chebyshev Polynomials have been recently proposed for assigning public key cryptosystems. G.J.Fee Et.al.[2] used Chebyshev Polynomial T n (x) for replacing monomial x n in Diffie-Helman and in RSA algorithms. Chebyshev polynomial can be mapped into classical discrete log problem. Based on Chebyshev Polynomial, we get RSA algorithm. Kai-Yuen Cheong [5] used Chebyshev polynomial to compare chaotic encryption systems with one-way functions to get new insights for chaos-based cryptosystems.K. Prasadh Et.al [9] described public key encryption based on Chebyshev polynomial. Proposed Method: Procedure for schedule round key generation: If two communicating parties want to communicate with each other first they agree upon to use a 8 digit decimal number to act as the secret key or main key for their communication. The 8 digit key is divided into two equal parts K