Abstract
ABSTRACT Stream ciphers are commonly used to provide confidentiality for a wide range of frame based applications such as mobile devices or embedded systems. For these applications, stream ciphers are preferred for encryption due to the simplicity of their implementation, efficiency and high throughput. However, practical attacks have been discovered on well-known stream ciphers. Many stream ciphers are designed to resist these attacks. The majority of these ciphers have a fixed structure, which is an advantage that their security against the known attacks can be proved. However, the fixed building structure of these ciphers also provides opportunities for potential new attacks. There have been a few approaches that have tried to add dynamicity to the structure of these ciphers to improve their security level. The idea behind this is that when the structures of ciphers are unknown to attackers, they are more resistant to attacks. However, these ciphers are not widely discussed among researchers. Moreover, the existing research concerning stream ciphers with dynamic structures has focused on dynamic polynomial switching in the Linear Feedback Shift Registers.