Özet:
Stream ciphers are an important class of encryption algorithms. They encrypt individual characters (usually binary digits) of a plaintext message one at a time, using an encryption transformation which varies with time. A stream cipher can not be considered suitable for cryptographic applications unless its output sequences have large periods, large linear complexities, high throughput rate and possess certain randomness properties. Moreover a stream cipher must provide high resistance against well known cryptanalytic attacks such as brute force, time-memory trade-off , correlation, algebraic and divide and conquer attacks. In this thesis, a new stream cipher GO is proposed. The main idea behind GO is that it uses two secret S-boxes while generating an output and an alternative bit search generator ( ABSG ) component to obtain a more secure keystream. Keystream properties of this algorithm and its resistance with respect to some well known cryptographic attacks is investigated. From the mathematical expressions and test results, it is shown that the new algorithm produces keystream sequences with satisfying basic security requirements and provide high resistance against currently known styles of attacks.
