Contributions to Confidentiality and Integrity Algorithms for 5G

The confidentiality and integrity algorithms in cellular networks protect the transmission of user and signaling data over the air between users and the network, e.g., the base stations. There are three standardised cryptographic suites for confidentiality and integrity protection in 4G, which are based on the AES, SNOW 3G, and ZUC primitives, respectively. These primitives are used for providing a 128-bit security level and are usually implemented in hardware, e.g., using IP (intellectual property) cores, thus can be quite efficient. When we come to 5G, the innovative network architecture and high-performance demands pose new challenges to security. For the confidentiality and integrity protection, there are some new requirements on the underlying cryptographic algorithms. Specifically, these algorithms should: 1) provide 256 bits of security to protect against attackers equipped with quantum computing capabilities; and 2) provide at least 20 Gbps (Gigabits per second) speed in pure software environments, which is the downlink peak data rate in 5G. The reason for considering software environments is that the encryption in 5G will likely be moved to the cloud and implemented in software. Therefore, it is crucial to investigate existing algorithms in 4G, checking if they can satisfy the 5G requirements in terms of security and speed, and possibly propose new dedicated algorithms targeting these goals. This is the motivation of this thesis, which focuses on the confidentiality and integrity algorithms for 5G. The results can be summarised as follows.1. We investigate the security of SNOW 3G under 256-bit keys and propose two linear attacks against it with complexities 2172 and 2177, respectively. These cryptanalysis results indicate that SNOW 3G cannot provide the full 256-bit security level. 2. We design some spectral tools for linear cryptanalysis and apply these tools to investigate the security of ZUC-256, the 256-bit version of ZUC. We propose a distinguishing attack against ZUC-256 with complexity 2236, which is 220 faster than exhaustive key search. 3. We design a new stream cipher called SNOW-V in response to the new requirements for 5G confidentiality and integrity protection, in terms of security and speed. SNOW-V can provide a 256-bit security level and achieve a speed as high as 58 Gbps in software based on our extensive evaluation. The cipher is currently under evaluation in ETSI SAGE (Security Algorithms Group of Experts) as a promising candidate for 5G confidentiality and integrity algorithms. 4. We perform deeper cryptanalysis of SNOW-V to ensure that two common cryptanalysis techniques, guess-and-determine attacks and linear cryptanalysis, do not apply to SNOW-V faster than exhaustive key search. 5. We introduce two minor modifications in SNOW-V and propose an extreme performance variant, called SNOW-Vi, in response to the feedback about SNOW-V that some use cases are not fully covered. SNOW-Vi covers more use cases, especially some platforms with less capabilities. The speeds in software are increased by 50% in average over SNOW-V and can be up to 92 Gbps.Besides these works on 5G confidentiality and integrity algorithms, the thesis is also devoted to local pseudorandom generators (PRGs). 6. We investigate the security of local PRGs and propose two attacks against some constructions instantiated on the P5 predicate. The attacks improve existing results with a large gap and narrow down the secure parameter regime. We also extend the attacks to other local PRGs instantiated on general XOR-AND and XOR-MAJ predicates and provide some insight in the choice of safe parameters

Revisiting LFSMs

Linear Finite State Machines (LFSMs) are particular primitives widely used in information theory, coding theory and cryptography. Among those linear automata, a particular case of study is Linear Feedback Shift Registers (LFSRs) used in many cryptographic applications such as design of stream ciphers or pseudo-random generation. LFSRs could be seen as particular LFSMs without inputs. In this paper, we first recall the description of LFSMs using traditional matrices representation. Then, we introduce a new matrices representation with polynomial fractional coefficients. This new representation leads to sparse representations and implementations. As direct applications, we focus our work on the Windmill LFSRs case, used for example in the E0 stream cipher and on other general applications that use this new representation. In a second part, a new design criterion called diffusion delay for LFSRs is introduced and well compared with existing related notions. This criterion represents the diffusion capacity of an LFSR. Thus, using the matrices representation, we present a new algorithm to randomly pick LFSRs with good properties (including the new one) and sparse descriptions dedicated to hardware and software designs. We present some examples of LFSRs generated using our algorithm to show the relevance of our approach.Comment: Submitted to IEEE-I

Execution Integrity with In-Place Encryption

Instruction set randomization (ISR) was initially proposed with the main goal of countering code-injection attacks. However, ISR seems to have lost its appeal since code-injection attacks became less attractive because protection mechanisms such as data execution prevention (DEP) as well as code-reuse attacks became more prevalent. In this paper, we show that ISR can be extended to also protect against code-reuse attacks while at the same time offering security guarantees similar to those of software diversity, control-flow integrity, and information hiding. We present Scylla, a scheme that deploys a new technique for in-place code encryption to hide the code layout of a randomized binary, and restricts the control flow to a benign execution path. This allows us to i) implicitly restrict control-flow targets to basic block entries without requiring the extraction of a control-flow graph, ii) achieve execution integrity within legitimate basic blocks, and iii) hide the underlying code layout under malicious read access to the program. Our analysis demonstrates that Scylla is capable of preventing state-of-the-art attacks such as just-in-time return-oriented programming (JIT-ROP) and crash-resistant oriented programming (CROP). We extensively evaluate our prototype implementation of Scylla and show feasible performance overhead. We also provide details on how this overhead can be significantly reduced with dedicated hardware support

Implementation and Benchmarking of a Crypto Processor for a NB-IoT SoC Platform

The goal of this Master’s Thesis is to investigate the implementation of cryptographic algorithms for IoT and how these encryption systems can be integrated in a NarrowBand IoT platform. Following 3rd Generation Partnership Project (3GPP) specifications, the Evolved Packet System (EPS) Encryption Algorithms (EEA) and EPS Integrity Algorithms (EIA) have been implemented and tested. The latter are based on three different ciphering algorithms, used as keystream generators: Advanced Encryption Standard (AES), SNOW 3G and ZUC. These algorithms are used in Long Term Evolution (LTE) terminals to perform user data confidentiality and integrity protection. In the first place, a thorough study of the algorithms has been conducted. Then, we have used Matlab to generate a reference model of the algorithms and the High-Level Synthesis (HLS) design flow to generate the Register-Transfer Level (RTL) description from algorithmic descriptions in C++. The keystream generation and integrity blocks have been tested at RTL level. The confidentiality block has been described along with the control, datapath and interface block at a RTL level using System C language. The hardware blocks have been integrated into a processor capable of performing hardware confidentiality and integrity protection: the crypto processor. This Intellectual Property (IP) has been integrated and tested in a cycle accurate virtual platform. The outcome of this Master’s Thesis is a crypto processor capable of performing the proposed confidentiality and integrity algorithms under request.The Internet of Things (IoT) is one of the big revolutions that our society is expected to go through in the near future. This represents the inter-connection of devices, sensors, controllers, and any items, refereed as things, through a network that enables machine-to-machine communication. The number of connected devices will greatly increase. The applications taking advantage of IoT will enable to develop a great amount of technologies such as smart homes, smart cities and intelligent transportation. The possibilities allowed are huge and not yet fully explored. Picture yourself in the near future having a nice dinner with some friends. Then, you suddenly recall that your parking ticket expires in five minutes and unfortunately your car is parked some blocks away. You are having a good time and feel lazy to walk all the way to where you parked your car to pay for a time extension. Luckily enough, the parking meter is part of the IoT network and allows you, with the recently installed new application in your smart-phone, to pay this bill from anywhere you are. This payment will be sent to the parking meter and your time will be extended. Problem solved, right? Well, the risk comes when you perform your payment, not knowing that your "worst enemy" has interceded this communication and is able to alter your transaction. Perhaps, this individual decides to cancel your payment and you will have to pay a fine. Or even worse, this person steals your banking details and uses your money to take the vacations you’ve always wanted. There are many examples in our everyday life where we expose our personal information. With an increasing number of devices existing and using wireless communications without the action of an human, the security is a key aspect of IoT. This Master’s Thesis addresses the need to cover these security breaches in a world where an increasing amount of devices are communicating with each other. With the expansion of IoT where billions of devices will be connected wirelessly, our data will be widely spread over the air. The user will not be able to protect their sensible data without these securing capabilities. Therefore, different security algorithms used in today’s and tomorrow’s wireless technologies have been implemented on a chip to secure the communication. The confidentiality and integrity algorithms aim to solve the two aspects of the problem: protect the secrecy of banking details and prevent the alteration of the communication’s information. In this Master’s Thesis we have developed a hardware processor for securing data during a wireless communication, specifically designed for IoT applications. The developed system is realized with minimal area and power in mind, so that they can be fitted even in the smallest devices. We have compared many different hardware architectures, and after exploring many possible implementations, we have implemented the security algorithms on a hardware platform. We believe the content of this Thesis work is of great interest to anybody interested in hardware security applied to the IoT field. Furthermore, due to the processes and methodology used in this work, it will also be of interest to people who want to know more about how higher level programming languages can be used to describe such a specialized circuit, like one performing security algorithms. Finally, people interested in hardware and software co-simulation will find in this project a good example of the utilization of such system modeling technique

Stream ciphers for secure display

In any situation where private, proprietary or highly confidential material is being dealt with, the need to consider aspects of data security has grown ever more important. It is usual to secure such data from its source, over networks and on to the intended recipient. However, data security considerations typically stop at the recipient's processor, leaving connections to a display transmitting raw data which is increasingly in a digital format and of value to an adversary. With a progression to wireless display technologies the prominence of this vulnerability is set to rise, making the implementation of 'secure display' increasingly desirable. Secure display takes aspects of data security right to the display panel itself, potentially minimising the cost, component count and thickness of the final product. Recent developments in display technologies should help make this integration possible. However, the processing of large quantities of time-sensitive data presents a significant challenge in such resource constrained environments. Efficient high- throughput decryption is a crucial aspect of the implementation of secure display and one for which the widely used and well understood block cipher may not be best suited. Stream ciphers present a promising alternative and a number of strong candidate algorithms potentially offer the hardware speed and efficiency required. In the past, similar stream ciphers have suffered from algorithmic vulnerabilities. Although these new-generation designs have done much to respond to this concern, the relatively short 80-bit key lengths of some proposed hardware candidates, when combined with ever-advancing computational power, leads to the thesis identifying exhaustive search of key space as a potential attack vector. To determine the value of protection afforded by such short key lengths a unique hardware key search engine for stream ciphers is developed that makes use of an appropriate data element to improve search efficiency. The simulations from this system indicate that the proposed key lengths may be insufficient for applications where data is of long-term or high value. It is suggested that for the concept of secure display to be accepted, a longer key length should be used

ECSC-128: New Stream Cipher Based On Elliptic Curve Discrete Logarithm Problem.

Ecsc-128 is a new stream cipher based on the intractability of the Elliptic curve discrete logarithm problem. The design of ECSC-l2g is divided into three important stages: Initialization Stage, Keystream Generation stage, and the Encryption Stage. The design goal of ECSC-128 is to come up with a secure stream cipher for data encryption. Ecsc-l2g was designed based on some hard mathematical problems instead of using simple logical operations. In terms of performance and security, Ecsc-l2g was slower, but it provided high level of security against all possible cryptanalysis attacks

International standards for stream ciphers: a progress report

The main objective of this paper is to review the current status of stream cipher standardisation. The hope is that, by doing so, the algorithms and techniques that are likely to be standardised at some point during the next year or so will be subjected to rigorous scrutiny by the crytopgraphic community