consider a 255-bit curve proposed by Bernstein known as Curve25519, which has also been adopted by the IETF. We optimize the X25519 key-exchange protocol proposed by Bernstein in 2006 for AVR ATmega 8-bit microcontrollers, MSP430X 16-bit microcontrollers, and for ARM Cortex-M0 32-bit microcontrollers. Our software for the AVR takes only 13,900,397 cycles for the computation of a Diffie-Hellman shared secret, and is the first to perform this computation in less than a second if clocked at 16 MHz for a security level of 128 bits. Our MSP430X software computes a shared secret in 5,301,792 cycles on MSP430X microcontrollers that have a 32-bit hardware multiplier and in 7,933,296 cycles on MSP430X microcontrollers that have a 16-bit multiplier. It thus outperforms previous constant-time ECDH software at the 128-bit security level on the MSP430X by more than a factor of 1.2 and 1.15, respectively. Our implementation on the Cortex-M0 runs in only 3,589,850 cycles and outperforms previous 128-bit secure ECDH software by a factor of 3.

Four-wave-mixing signals from excitons under linear-circular polarized excitation exhibit an elliptical polarization, depending on both the pulse delay and the spectral position. Besides the resonances corresponding to excitons and exciton-biexciton transitions, a breakup of the exciton line is found reflecting the influence of correlations on the four-point level. An analysis accounting for the exciton density, the bound biexciton, and the exciton-exciton scattering continuum reveals that these features are not due to an antibound two-exciton state. Instead, they result from an interference of the correlated exciton continuum with the exciton density. In addition, the modeling shows that the signals ellipticity is highly sensitive to the influences of different correlations and, therefore, allows for a discrimination of their contributions. [S0031-9007(98)08064-8] PACS numbers: 71.35. Gg, 42.50.Md, Quantum kinetic effects have a key role in revealing the quantum nature of the matter light interaction. Therefore, the search for distinct experimental fingerprints of correlated quantum kinetics beyond the scope of the Boltzmann equation or time-dependent Hartree-Fock theory has attracted much attention in recent years [1][2][3][4][5][6][7]. So far, firm evidence for phonon quantum kinetics has been found by demonstrating the occurrence and the controllability [2] of phonon sidebands and by a demonstration of the limits imposed by the energy-time uncertainty [4,5]. Also for the case of Coulomb quantum kinetics in the high excitation regime specific predictions have been made [7], namely, that time-resolved four-wave-mixing (FWM) spectra should show a sideband having a frequency which scales with the plasma frequency. However, this prediction has not been experimentally verified up to now.The dynamics of biexcitonic contributions to FWM on the other hand is a prominent example related to Coulomb quantum kinetics at moderate excitation densities [8][9][10][11][12][13][14]. Recently, the dependence of the exciton-exciton correlation in the scattering state continuum on a magnetic field has been investigated [11]. In this Letter we demonstrate that even for moderate excitation the correlated Coulomb quantum kinetics leads to significant effects the description of which requires one to go beyond the coherent limit. In particular, the combined dynamics of the correlated two-pair scattering continuum and exciton densities, the latter having lost their interband coherence, leads to characteristic spectral signatures of the polarization state of FWM signals. The almost perfect agreement between calculated and experimental data obtained from ZnSe quantum wells allows one to draw a conclusive picture of the processes relevant for the signal generation.Spectrally resolved degenerate FWM experiments are performed on a 7.5 nm thin ZnSe͞ZnS 0.06 Se 0.94 singlequantum-well sample grown by molecular-beam epitaxy lattice matched to subsequently removed GaAs substrates. The exciton binding energy amounts to 20 meV. Pulses from a frequ...

The memory structure induced by coherent transitions to the exciton-exciton scattering continuum is shown to have significant influence on spectrally resolved four-wave-mixing signals even under selective excitation of 1s excitons. Comparisons between experiments and calculations that account nonperturbatively for these quantum kinetic Coulomb correlations demonstrate large compensations between mean-field contributions and transitions to the two-pair continuum. Experiments with different polarizations of the laser pulses show that two-pair continuum correlations are responsible for delay-time dependent shifts of the excitonic emission as well as for substantial deformations of the line shape.

Increasingly connectivity becomes integrated in products and devices that previously operated in a stand-alone setting. This observation holds for many consumer applications in the so-called "Internet of Things" (IoT) as well as for corresponding industry applications (IIoT), such as industrial process sensors. Often the only practicable means for authentication of human users is a password. The security of password-based authentication schemes frequently forms the weakest point of the security infrastructure. In this paper we first explain why a tailored protocol designed for the IIoT use case is considered necessary. The differences between IIoT and the conventional Internet use-cases result in largely modified threats and require special procedures for allowing both, convenient and secure use in the highly constrained industrial setting. Specifically the use of a verifier-based password-authenticated key-exchange (V-PAKE) protocol as a hedge against public-key-infrastructure (PKI) failures is considered important. Availability concerns for the case of failures of (part of) the communication infrastructure makes local storage of access credentials mandatory. The larger threat of physical attacks makes it important to use memory-hard password hashing. This paper presents a corresponding tailored protocol, AuCPace, together with a security proof within the Universal Composability (UC) framework considering fully adaptive adversaries. We also introduce a new security notion of partially augmented PAKE that provides specific performance advantages and makes them suitable for a larger set of IIoT applications. We also present an actual instantiation of our protocol, AuCPace25519, and present performance results on ARM Cortex-M0 and Cortex-M4 microcontrollers. Our implementation realizes new speed-records for PAKE and X25519 Diffie-Hellman for the ARM Cortex M4 architecture.

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