Exchange-enhanced Ultrastrong Magnon-Magnon Coupling in a Compensated Ferrimagnet

The ultrastrong coupling of (quasi-)particles has gained considerable attention due to its application potential and richness of the underlying physics. Coupling phenomena arising due to electromagnetic interactions are well explored. In magnetically ordered systems, the quantum-mechanical exchange-interaction should furthermore enable a fundamentally different coupling mechanism. Here, we report the observation of ultrastrong intralayer exchange-enhanced magnon-magnon coupling in a compensated ferrimagnet. We experimentally study the spin dynamics in a gadolinium iron garnet single crystal using broadband ferromagnetic resonance. Close to the ferrimagnetic compensation temperature, we observe ultrastrong coupling of clockwise and anticlockwise magnon modes. The magnon-magnon coupling strength reaches more than 30% of the mode frequency and can be tuned by varying the direction of the external magnetic field. We theoretically explain the observed phenomenon in terms of an exchange-enhanced mode-coupling mediated by a weak cubic anisotropy

Domain-Oriented Masking: Compact Masked Hardware Implementations with Arbitrary Protection Order

Passive physical attacks, like power analysis, pose a serious threat to the security of embedded systems and corresponding countermeasures need to be implemented. In this work, we demonstrate how the costs for protecting digital circuits against passive physical attacks can be lowered significantly. We introduce a novel masking approach called domain-oriented masking (DOM). Our approach provides the same level of security as threshold implementations (TI), while it requires less chip area and less randomness. DOM can also be scaled easily to arbitrary protection orders for any circuit. To demonstrate the flexibility of our scheme, we apply DOM to a hardware design of the Advanced Encryption Standard (AES). The presented AES implementation is built in a way that it can be synthesized for any protection order. Although the design is scalable, it leads to the smallest (7.1 kGE), fastest, and least randomness demanding (18 bits) first-order secure AES implementation. The gap between DOM and TI increases with the protection order. Our second-order secure AES S-box implementation, for example, has a hardware footprint that is half the size of the smallest existing second-order TI of the S-box. This paper includes synthesis results of our AES implementation up to the 15th protection order

Higher-Order Side-Channel Protected Implementations of Keccak

The efficient protection of security critical devices against side-channel analysis attacks is a fundamental need in the age of Internet of Things and ubiquitous computing. In this work, we introduce a configurable hardware design of Keccak (SHA-3) which can be tailored to fulfill the needs of a wide range of different applications. Our Keccak design is therefore equipped with generic side-channel protection capabilities. The design can thus be synthesized for any desired protection level by just changing one design parameter. Regardless of its generic appearance, the introduced Keccak design yields the smallest (15.7 kGE) firstorder protected Keccak implementation published to this date. Furthermore, it is to the best of our knowledge the first higher-order side-channel resistant implementation of Keccak. In total, we state results for four different Keccak variants up to the ninth protection order

Privacy-Aware Authentication in the Internet of Things

Besides the opportunities o ered by the all-embracing Internet of Things (IoT) technology, it also poses a tremendous threat to the privacy of the carriers of these devices. In this work, we build upon the idea of an RFID-based IoT realized by means of standardized and well-established Internet protocols. In particular, we demonstrate how the Internet Protocol Security protocol suite (IPsec) can be applied in a privacy-aware manner. Therefore, we introduce a privacy-aware mutual authentication protocol compatible with restrictions imposed by the IPsec standard and analyze its privacy and security properties. In order do so, we revisit and adapt the RFID privacy model (HPVP) of Hermans et al. (ESORICS\u2711). With this work, we show that privacy in the IoT can be achieved without relying on proprietary protocols and on the basis of existing Internet standards

Concealing Secrets in Embedded Processors Designs

Side-channel analysis (SCA) attacks pose a serious threat to embedded systems. So far, the research on masking as a countermeasure against SCA focuses merely on cryptographic algorithms, and has either been implemented for particular hardware or software implementations. However, the drawbacks of protecting specific implementations are the lack of flexibility in terms of used algorithms, the impossibility to update protected hardware implementations, and long development cycles for protecting new algorithms. Furthermore, cryptographic algorithms are usually just one part of an embedded system that operates on informational assets. Protecting only this part of a system is thus not sufficient for most security critical embedded applications. In this work, we introduce a flexible, SCA-protected processor design based on the open-source V-scale RISC-V processor. The introduced processor design can be synthesized to defeat SCA attacks of arbitrary attack order. Once synthesized, the processor protects the computation on security-sensitive data against side-channel leakage. The benefits of our approach are (1) flexibility and updatability, (2) faster development of SCA-protected systems, (3) transparency for software developers, (4) arbitrary SCA protection level, (5) protection not only for cryptographic algorithms, but against leakage in general caused by processing sensitive data

Ab Initio Second-Order Nonlinear Optics in Solids: Second-Harmonic Generation Spectroscopy from Time-Dependent Density-Functional Theory

We present in detail the formulation of the ab initio theory we have developed for the calculation of the macroscopic second-order susceptibility $\chi^{(2)}$. We find a general expression for $\chi^{(2)}$ valid for any fields, containing the ab initio relation between the \textit{microscopic} and \textit{macroscopic} formulation of the second-order responses. We consider the long wavelength limit and we develop our theory in the Time-Dependent Density-Functional Theory framework. This allows us to include straightforwardly many-body effects such as crystal local-field and excitonic effects. We compute the Second-Harmonic Generation spectra for the cubic semiconductors SiC, AlAs and GaAs and starting from the Independent-Particle Approximation for $\chi^{(2)}$, we include quasiparticle effects via the scissors operator, crystal local-field and excitonic effects. In particular, we consider two different types of kernels: the ALDA and the "long-range" kernel. We find good agreement with other theoretical calculations and experiments presented in literature, showing the importance of very accurate description of the many-body interactions