A New Stream Cipher HC-256

HC-256 is a software-efficient stream cipher. It generates keystream from a 256-bit secret key and a 256-bit initialization vector. The encryption speed of the C implementation of HC-256 is about 1.9 bits per clock cycle (4.2 cycle/byte) on the Intel Pentium 4 processor. A variant of HC-256 is also introduced in this paper

Cryptanalysis of Symmetric Cryptographic Primitives

Symmetric key cryptographic primitives are the essential building blocks in modern information security systems. The overall security of such systems is crucially dependent on these mathematical functions, which makes the analysis of symmetric key primitives a goal of critical importance. The security argument for the majority of such primitives in use is only a heuristic one and therefore their respective security evaluation continually remains an open question. In this thesis, we provide cryptanalytic results for several relevant cryptographic hash functions and stream ciphers. First, we provide results concerning two hash functions: HAS-160 and SM3. In particular, we develop a new heuristic for finding compatible differential paths and apply it to the the Korean hash function standard HAS-160. Our heuristic leads to a practical second order collision attack over all of the HAS-160 function steps, which is the first practical-complexity distinguisher on this function. An example of a colliding quartet is provided. In case of SM3, which is a design that builds upon the SHA-2 hash and is published by the Chinese Commercial Cryptography Administration Office for the use in the electronic authentication service system, we study second order collision attacks over reduced-round versions and point out a structural slide-rotational property that exists in the function. Next, we examine the security of the following three stream ciphers: Loiss, SNOW 3G and SNOW 2.0. Loiss stream cipher is designed by Dengguo Feng et al. aiming to be implemented in byte-oriented processors. By exploiting some differential properties of a particular component utilized in the cipher, we provide an attack of a practical complexity on Loiss in the related-key model. As confirmed by our experimental results, our attack recovers 92 bits of the 128-bit key in less than one hour on a PC with 3 GHz Intel Pentium 4 processor. SNOW 3G stream cipher is used in 3rd Generation Partnership Project (3GPP) and the SNOW 2.0 cipher is an ISO/IEC standard (IS 18033-4). For both of these two ciphers, we show that the initialization procedure admits a sliding property, resulting in several sets of related-key pairs. In addition to allowing related-key key recovery attacks against SNOW 2.0 with 256-bit keys, the presented properties reveal non-random behavior of the primitives, yield related-key distinguishers for the two ciphers and question the validity of the security proofs of protocols based on the assumption that these ciphers behave like perfect random functions of the key-IV. Finally, we provide differential fault analysis attacks against two stream ciphers, namely, HC-128 and Rabbit. In this type of attacks, the attacker is assumed to have physical influence over the device that performs the encryption and is able to introduce random faults into the computational process. In case of HC-128, the fault model in which we analyze the cipher is the one in which the attacker is able to fault a random word of the inner state of the cipher but cannot control its exact location nor its new faulted value. Our attack requires about 7968 faults and recovers the complete internal state of HC-128 by solving a set of 32 systems of linear equations over Z2 in 1024 variables. In case of Rabbit stream cipher, the fault model in which the cipher is analyzed is the one in which a random bit of the internal state of the cipher is faulted, however, without control over the location of the injected fault. Our attack requires around 128 − 256 faults, precomputed table of size 2^41.6 bytes and recovers the complete internal state of Rabbit in about 2^38 steps

Improved distinguishers for HC-128

HC-128 is an eSTREAM final portfolio stream cipher. Several authors have investigated its security and, in particular, distinguishing attacks have been considered. Still, no one has been able to provide a distinguisher stronger than the one presented by Wu in the original HC-128 paper. In this paper we first argue that the keystream requirement in Wu’s original attack is underestimated by a factor of almost 2^8. Our revised analysis shows that the keystream complexity of Wu’s original attack is 2^160.471 32-bit keystream blocks. We then go on to investigate two new types of distinguishers on HC-128. One of them, a distinguisher counting the number of zeros in created blocks of bits, gives a biased distribution that requires 2^143.537 such constructed block samples (2^152.537 32-bit keystream blocks). For fairness, the same metric is used to compare our attack to Wu’s, and our improvement is significant compared to Wu’s original result. Furthermore, the vector-based methodology used is general and can be applied to any cryptographic primitive that reveals a suitable probability distribution

Freestyle, a randomized version of ChaCha for resisting offline brute-force and dictionary attacks

This paper introduces Freestyle, a randomized and variable round version of the ChaCha cipher. Freestyle uses the concept of hash based halting condition where a decryption attempt with an incorrect key is likely to take longer time to halt. This makes Freestyle resistant to key-guessing attacks i.e. brute-force and dictionary based attacks. Freestyle demonstrates a novel approach for ciphertext randomization by using random number of rounds for each block, where the exact number of rounds are unknown to the receiver in advance. Freestyle provides the possibility of generating $2^{128}$ different ciphertexts for a given key, nonce, and message; thus resisting key and nonce reuse attacks. Due to its inherent random behavior, Freestyle makes cryptanalysis through known-plaintext, chosen-plaintext, and chosen-ciphertext attacks difficult in practice. On the other hand, Freestyle has costlier cipher initialization process, typically generates 3.125% larger ciphertext, and was found to be 1.6 to 3.2 times slower than ChaCha20. Freestyle is suitable for applications that favor ciphertext randomization and resistance to key-guessing and key reuse attacks over performance and ciphertext size. Freestyle is ideal for applications where ciphertext can be assumed to be in full control of an adversary, and an offline key-guessing attack can be carried out

SAFE-NET: Secure and Fast Encryption using Network of Pseudo-Random Number Generators

We propose a general framework to design a general class of random number generators suit- able for both computer simulation and computer security applications. It can include newly pro- posed generators SAFE (Secure And Fast Encryption) and ChaCha, a variant of Salsa, one of the four finalists of the eSTREAM ciphers. Two requirements for ciphers to be considered se- cure is that they must be unpredictable with a nice distributional property. Proposed SAFE-NET is a network of n nodes with external pseudo-random number generators as inputs nodes, several inner layers of nodes with a sequence of random variates through ARX (Addition, Rotation, XOR) transformations to diffuse the components of the initial state vector. After several rounds of transformations (with complex inner connections) are done, the output layer with n nodes are outputted via additional transformations. By utilizing random number generators with desirable empirical properties, SAFE-NET injects randomness into the keystream generation process and constantly updates the cipher’s state with external pseudo-random numbers during each iteration. Through the integration of shuffle tables and advanced output functions, extra layers of security are provided, making it harder for attackers to exploit weaknesses in the cipher. Empirical results demonstrate that SAFE-NET requires fewer operations than ChaCha while still producing a sequence of uniformly distributed random numbers

RC4 Encryption-A Literature Survey

AbstractA chronological survey demonstrating the cryptanalysis of RC4 stream cipher is presented in this paper. We have summarized the various weaknesses of RC4 algorithm followed by the recently proposed enhancements available in the literature. It is established that innovative research efforts are required to develop secure RC4 algorithm, which can remove the weaknesses of RC4, such as biased bytes, key collisions, and key recovery attacks on WPA. These flaws in RC4 are still offering an open challenge for developers. Hence our chronological survey corroborates the fact that even though researchers are working on RC4 stream cipher since last two decades, it still offers a plethora of research issues. The attraction of community towards RC4 is still alive

A dynamic data encryption method based on addressing the data importance on the internet of things

The rapid growth of internet of things (IoT) in multiple areas brings research challenges closely linked to the nature of IoT technology. Therefore, there has been a need to secure the collected data from IoT sensors in an efficient and dynamic way taking into consideration the nature of collected data due to its importance. So, in this paper, a dynamic algorithm has been developed to distinguish the importance of data collected and apply the suitable security approach for each type of data collected. This was done by using hybrid system that combines block cipher and stream cipher systems. After data classification using machine learning classifiers the less important data are encrypted using stream cipher (SC) that use rivest cipher 4 algorithm, and more important data encrypted using block cipher (BC) that use advanced encryption standard algorithm. By applying a performance evaluation using simulation, the proposed method guarantees that it encrypts the data with less central processing unit (CPU) time with improvement in the security over the data by using the proposed hybrid system