Remote attestation is a powerful mechanism that allows a verifier to know if the hardware of an IoT (Internet-of-Thing) device (acting as a prover) has been counterfeited or tampered with and if its firmware has been altered. Remote attestation is based on collecting and reporting measurements in a trusted way, and should be lightweight for resource-constrained IoT devices. This work proposes to include a low-cost Root of Trust for Measuring and Reporting (RoTMR) in the prover, based on the combination of a Physically Unclonable Function (PUF) and an Attestation Read-Only Memory (A-ROM), and to use hash-based digital signatures in the attestation protocol. The proposed RoTMR is addressed to IoT devices based on a microcontroller that executes some application code (the measurable object) located in an external non-volatile memory accessible by an attacker. The secret keys required by the digital signatures are not stored but reconstructed using the PUF. The A-ROM contains the attestation instructions and ensures that its contents cannot be altered and that its instructions are executed sequentially without modification. The use of hash-based digital signatures makes the solution quantum-resistant and very robust because its security relies solely on the unidirectionality of a hash function. The proposed attestation protocol takes advantage of the fact that One-Time Signature (OTS) generation and Many-Time Signature (MTS) verification are very well suited for low-end devices, and the MTS scheme is suitable for the verifier application context. The proposal was validated experimentally with the ESP32 microcontroller, which is widely employed in IoT devices, by using its SRAM as PUF and implementing WOTS+, which is a type of Winternitz One-Time Signature scheme (WOTS), the One-Time Signature of Smart Digital Signatures scheme (SDS-OTS), and the MTS schemes constructed with them. The OTS schemes require smaller codes and thus smaller A-ROM than MTS and ECDSA (Elliptic Curve Digital Signature Algorithm). The code of one of the WOTS+ takes about 4 times less space than ECDSA. In terms of execution times, the OTS schemes are very fast. One of the WOTS+ performs all the signature operations in a few tens of milliseconds. The OTS schemes (especially the SDS-OTS) are also very efficient in terms of communication bandwidth because they use small signatures compared to other post-quantum solutions.

Physically unclonable functions (PUFs) and true random number generators (TRNGs) are cryptographic primitives very well suited for secure IoT devices. This article proposes a circuit, named multibit-RO-PUF-TRNG, which offers the advantages of unifying PUF and TRNG in the same design. It is based on counting the oscillations of pairs of ring oscillators (ROs), one of them acting as a reference. Once the counter of the reference oscillator reaches a fixed value, the count value of the other RO is employed to provide the TRNG and the multibit PUF response. A mathematical model is presented that supports not only the circuit foundations but also a novel and simple calibration procedure that allows optimizing the selection of the design parameters. Experimental results are illustrated with large data sets from two families of FPGAs with different process nodes (90 and 28 nm). These results confirm that the proposed calibration provides TRNG and PUF responses with high quality. The raw TRNG bits do not need post-processing and the PUF bits (even 6 bits per RO) show very small aliasing. In the application context of obfuscating and reconstructing secrets generated by the TRNG, the multibit PUF response, together with the proposal of using error-correcting codes and RO selection adapted to each bit, provide savings of at least 79.38% of the ROs compared to using a unibit PUF without RO selection. The proposal has been implemented as an APB peripheral of a VexRiscv RV32I core to illustrate its use in a secure FPGA-based IoT device.

This paper describes a demonstrator of a post-quantum-secure facial authentication system distributed between a mobile device acting as a client and a remote computer acting as an authentication server. Homomorphic encryption based on Classic McEliece, one of the fourth-round candidates of the NIST post-quantum standardization process, is carried out by the client for protecting the biometric data extracted from the users' faces at enrollment and verification. The remote computer only stores and compares the received protected data, thus preserving user privacy. An Android App and a Graphical User Interface (GUI) were implemented at the client and the server, respectively, to show the system performance in terms of computation and security.

The Aerosol Optical Depth (AOD) is a very important atmospheric parameter which knowledge will help to understand the atmospheric processes and to propose different scenarios related with climate change. AOD plays a main role in the energy radiation balance in the atmosphere and in the aerosol radiative forcing. In this paper an analysis of time series of AOD, from MYD04_3K (MODIS Aqua Aerosols product gridded in a resolution of 3 kilometres), is analysed by means of Fourier Harmonics tool. Results shown in this paper are preliminary results because a more comprehensive study is envisaged where data coming from sun and lunar photometers installed in Artic stations will be analysed jointly.

A 1-D radiative transfer study is presented based on the measurements performed at Granada during a dust event within the framework of the ChArMEx/ADRIMED (Chemistry-Aerosol Mediterranean Experiment/Aerosol Direct Radiative Forcing on the Mediterranean Climate) campaign, during June 16-17, 2013. Ground-based AERONET and lidar measurements were performed and further processed with the GRASP algorithm to get spectrally-resolved profiles of extinction and single scattering albedo. Furthermore, the research aircraft ATR-42 made two flights above Granada providing vertical profiles of aerosol optical and microphysical properties together with measurements of broadband radiative fluxes. All of the ground-based and aircraft aerosol properties are used as input in the radiative transfer model GAME in order to evaluate its sensitivity to different input datasets. The aircraft fluxes are used for validation of the modelled ones.

The aerosol extinction profiles at Granada (Spain) have been obtained combining ceilometer and sun/sky measurements in the GRASP code. In order to see the goodness of these retrieved profiles, three photometers at different altitudes have been used. The aerosol optical depth (AOD) at different height layers have been calculated with these photometers and it has been compared against the integrated retrieved extinction at the same layers. The obtained AOD (from GRASP and from photometers at different altitudes) correlates well, showing the most of r2values above 0.6. The differences between both AOD values indicates that the retrieved aerosol extinction profiles are within the uncertainty of the photometers but this method overestimates the extinction at low levels and underestimates at high levels.

This work deals with the validation of integrated water vapor (IWV) products derived from the following satellite instruments: Global Ozone Monitoring Instrument (GOME-2), Moderate-Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites, Ozone Monitoring Instrument (OMI), Spining Enhanced Visible and InfraRed Imager (SEVIRI), Atmospheric Infrared Sounder (AIRS), and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). IWV data from GPS in nine ground-based stations located in the Iberian Peninsula are used as reference. The study period extends from 2007 to 2012, under cloud-free conditions. All satellite instruments showed a tendency to reduce IWV extreme values: low IWV is overestimated while high IWV is underestimated. As for the influence of solar zenith angle (SZA), Seasonal dependence is mainly due to the SZA and IWV typical values in each season. In general, in summer the tendency is to underestimate with low inter-quartile range (IQR) and in winter the trend is to overestimate with high IQR.