The Designs Of Stream Cipher Based On FCSR And Their Analysis

The Feedback with Carry Shift Registers (FCSR for short) has the similar structure with Linear Feedback Shift Registers (LFSR for short), but its generated sequence has high linear complexity by using addition with carry. Now it is very popular to design the stream cipher by means of nonlinear components. So, as an important nonlinear component, the FCSR is playing a key role in stream cipher design.This thesis focuses on the usage of FCSR as keystream generator in stream cipher. Firstly based on the properties of FCSR, we study a keystream generator-F-FCSR-Hv2and improve it in two ways, and then propose two generators—Combined F-FCSR keystream generator and Dynamic filter keystream generator DF-FCSR-8. Next, we use FCSR in clock control instead of LFSR, which show better property than those based on LFSR. Combining the dynamic filter generator and clock controlled generator, we build a new type of keystream generator. Finally, aiming the Radio Frequency Identification (RFID for short) technology and the light weight certification scheme-SQUASH, we present a new certification scheme based on FCSR called SQUASH+, and a scheme called SQUASH+DF-FCSR for both certification and encryption, which is combination of the SQUASH+and the light weighted DF-FCSR.The main result of this thesis is as follows:1. Based on the properties of F-FCSR-Hv2generator and analysis of the Hell-Johansson attack which is an effective attack for F-FCSR-Hv2, an improved generator for filtered FCSR generator called Combined F-FCSR generator is presented. This generator maintains high output rate and good property at the cost of increasing more registers, and is resistant to Hell-Johansson attack and other attacks as well.2. A new generator named dynamic filtered generator DF-FCSR-8is proposed. This generator uses dynamic filter as the filter of an FCSR’s main register instead of the original static one. Because the filter is changed each time, the attacker cannot acquire enough linear functions so that this generator can resist Hell-Johansson attack. Other analyses indicate that DF-FCSR-8can withstand the correlation attack, algebraic attack and other attacks. While the test shows that DF-FCSR-8has good statistic characteristics.3. Using FCSR to construct clock controlled generator instead of LFSR, two genera-tors:Stop and Go generator based on FCSR and Alternating Step generator based on FCSR, are proposed. This thesis gives the parameters of those generators, the period of generated sequence, lower bound of linear complexity, the ability against Hell-Johansson attack and other attacks, and statistic properties. Those results show that Stop and Go generator has a large period and high lower bound of linear complexity, but less good statistic property, while Alternating Step Generator has large period, high lower bound of linear complexity, good statistic properties, and ability to against Hell-Johansson attack and other attacks.4. With the combination of dynamic filtered generator and clock controlled generator, two generators:SGDF-FCSR-8and ASDF-FCSR-8, are developed. The former is a combi-nation of Stop and Go generator and dynamic filtered generator; the later is a combination of Alternating Step generator and dynamic filtered generator. This thesis gives the parameters, the period of generated sequence, lower bound of linear complexity, and the ability against Hell-Johansson attack and other attacks, and also tests statistic properties of both generators. Although SGDF-FCSR-8has better statistic property than Stop and Go generator, it does not pass all the tests. WhereasASDF-FCSR-8improves the output rate based on a large period of Alternating Step Generator, and also has high lower bound on linear complexity and good statistic properties.5. Through the investigation of a lightweight certification scheme, SQUASH, which is used in RFID environment, an improved version SQUASH+is given based on FCSR and standard SQUASH in this thesis. This scheme can complete the computation much more effi-ciently while ensuring the security. After that, considering the SQUASH+and the properties of stream-cipher based on FCSR, this thesis give a lightweight scheme named SQUASH+DF-FCSR which uses the FCSR as the data generator. The calculation process for certification is also initializing the keystream generator, and then encrypts the data. The FCSR is employed for both the certification and encryption, which makes the scheme more effective and use less memory. This scheme is a good practical lightweight scheme combined with certification and encryption in RFID environment.The proposed keystream generator in this thesis can be used in some environment with limited resources, such as sensor network, Ad-Hoc wireless communication net work and RFID environment..