313,725 research outputs found
Equivalent Capacity-Based Joint Multilevel Coding and Space–Time Transmit Diversity Design
No full textTEE - The Electronic Exercise
No full textThe Electronic Exercise (TEE) is an experimental adaptive learning system which uses knowledge structures to apply an intelligent tutoring algorithm and especially the representation of its surmise relation via HASSE diagrams to navigate within the learning material, to visualize the learning progress and convey the structure itself to the learner. TEE is implemented via dynamic HTML and comes with an editor tool for the structure and the test exercises. Thus an author or teacher can build its own TEE system easily
Analysis of Reentrant Hybrid Tee
No full textThe conventional hybrid tee, which is symmetrical and reciprocal, has been used exclusively in mixer and impedance bridges in microwave engineering. The interconnection of the E-arm and H-arm of the hybrid tee through a 90-degree twist and a phase-shifter by Ishii and Jenners has turned the magic tee into a reentrant hybrid tee with different properties. Ishii and Jenners\u27 paper on the different attenuation levels of port 1 and port 2 of the reentrant hybrid tee has aroused the public interest about the characteristics of the reentrant hybrid tee. It is intended in this study to investigate the characteristics of the reentrant hybrid tee experimentally and theoretically. In the experiment, the author has done the measurements about attenuation, VSWR and impedance against the variation of frequency or phase-shifter setting of the reentrant loop. In theory, the author has derived a general equation for the reentrant hybrid tee, in terms of the scattering parameters of a basic hybrid tee. Conclusions were made about the reentrant hybrid tee by combining the experimental results and theoretical equations
Reflection Co-Efficients of Re-Entrant Hybrid Tee
No full textThe conventional hybrid tee is a result of the combination of the E- plane tee and the H- plane tee into one device. The E-H hybrid tee has wide application as impedance bridge, Duplexer, mixer, discriminator, and in cascading of one port amplifier. The field of study in the hybrid tee was widened by introduction of the E-H reentrant tee which interconnects the E and H ports. Such a loop has been studied with reflectionless load. The author has extended the field of study of the E- H reentrant tee to the case of shorting load. A whole new reentrant tee has also been experimented on by interconnecting the collinear ports instead of the E-H ports. This study will help further work on the collinear hybrid tee
Assessment of damage tolerance levels in FRP ship structures
No full textThis work is concerned with the damage tolerance assessment of laminated composite structures used in ship structures. An intensive review has been carried out with regard to current experimental, analytical and numerical work on both laminates and structural elements. Particular attention has been focused on the problem of damage due to delamination and its structural consequences. Strength assessments of top hat stiffeners and tee joints has been carried out with a view to identifying regions most susceptible to delaminations. It has been shown that such regions are contained within the curved region of the overlaminate in both types of structural elements. Strain energy release rates and J-integral values have been calculated for specific cracks to determine their likelihood of propagation under a variety of loading conditions. Overall, a number of conclusions have been drawn with regard to single-skin marine FRP structures. For example, both the strength - and the energy - based approaches have predicted that a tee joint subjected to a 45 degree pull-off load, delaminations which are deep within the overlaminate are more likely to propagate than those close to the surface
Tee, J E, VX61461
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/420815Surname: TEE. Given Name(s) or Initials: J E. Military Service Number or Last Known Location: VX61461. Missing, Wounded and Prisoner of War Enquiry Card Index Number: 39434.245525
Item: [2016.0049.53076] "Tee, J E, VX61461
TZ logger. A multi-platform TEE logger
No full textLAUREA MAGISTRALEI Trusted Execution Environments (TEEs, Ambienti di esecuzione sicura) sono comunemente usati per gestire dati ed operazioni sensibili nei dispositivi mobili. Un TEE è un ambiente di esecuzione separato che fornisce un piccolo insieme di servizi. Questi servizi possono continuare la loro esecuzione senza essere compromessi anche quando il sistema operativo (OS, operative system) principale, chiamato anche "_ricco_" ( Rich ), è completamente compromesso. Nei sistemi Android, le TEEs sono tipicamente implementate usando la tecnologia ARM TrustZone, mentre il sistema operative principale è basato su Linux.
Teoricamente, un malintenzionato capace di compromettere completamente il Rich OS di un dispositivo non dovrebbe essere in grado di interferire con le operazioni gestite dal TEE. Tuttavia, è stato mostrato che, in casi specifici [][#broken_fingers], un malintenzionato in grado di compromettere completamente il Rich OS ( ottenendo esecuzione arbitraria al livello del kernel ) può manomettere il canale di comunicazione tra il Rich OS ed il TEE, e, di conseguenza, interferire con i servizi e le periferiche gestite dal TEE.
Per esempio, consideriamo la funzionalità di sblocco con impronta digitale supportato da molti dispositivi moderni. La scansione e confronto dell'impronta sono completamente gestiti dal TEE e perciò fuori dalla portata del nostro modello di attaccante. Tuttavia, quando TEE riconosce che un utente legittimo ha toccato il sensore, un messaggio costante viene inviato dal TEE al Rich OS, il quale procede allo sblocco del dispositivo. Siccome il messaggio è costante (i.e., nessuna firma crittografica è generata dal TEE per confermare l'autore del messaggio di sblocco ), un malintenzionato che ha completamente compromesso il Rich OS può facilmente falsificare questo messaggio e sbloccare il dispositivo senza che un utente legittimo abbia toccato il sensore.
L'obiettivo principale della nostra ricerca è dimostrare che molte delle funzionalità offerte dai TEEs non sono resistenti ad un attacco con permessi di esecuzione nel kernel del Rich OS. Con questo scopo, svilupperemo un modulo per il kernel che intercetta e registra tutti i messaggi scambiati tra TEE ed il Rich OS. Questi registri verranno poi utilizzati per studiare i dati scambiati, cercando casi problematici in modo semi-automatico. In particolar modo, la nostra intuizione è che i casi problematici ( come quello precedentemente menzionato della funzionalità di sblocco con impronta digitale ) possono essere automaticamente evidenziati analizzando i registri e rilevando risposte costanti dal TEE al Rich OS, poiché l'attaccante può facilmente manomettere questi messaggi.
Implementeremo il nostro logger ( registratore ), chiamato **TZ Logger**, in maniera modulare ed estensibile che permetta di ispezionare e modificare i dati scambiati con il TEE. La sua architettura permette di adattarsi velocemente a diversi dispositivi e versioni del sistema operativo. Esso consente inoltre di scrivere rapidamente dei moduli “dissector” per deserializzare alcuni tipi specifici di messaggi scambiati tra il Rich OS e TEE ( e.g., messaggi crittografici, messaggi relativi al sensore delle impronte digitali, ... ) e dei moduli “patcher” che si occupano di mutare i messaggi scambiati a piacere.
Siamo riusciti ad utilizzare un prototipo preliminare di **TZ Logger** per dimostrare con successo che un attaccante con esecuzione di codice nel kernel può sbloccare il dispositivo. Questo senza che un utente legittimo scansioni la propria impronta digitale e senza aver compromesso il codice all'interno del TEE.Trusted Execution Environments (TEEs) are commonly used to handle security-sensitive data and operations in mobile devices. A TEE is a separate execution environment that provides a small set of services. These services can run uncompromised even when the main (rich) OS has been entirely compromised. In Android systems, TEEs are typically implemented using the ARM TrustZone technology and the main OS is based on Linux.
In theory, an attacker able to fully compromise the main OS of a device should not be able to interfere with operations handled by the TEE. However, it has been shown that, in specific cases [][#broken_fingers], an attacker able to fully compromise the main OS (a kernel-level attacker) can tamper the communication channel between the main OS and the TEE, and, consequently, interfere with TEE-managed services and peripherals.
For instance, consider the case of the fingerprint-unlock functionality supported by many modern devices. The fingerprint scanning and matching operations are fully handled by the TEE and therefore out of scope in our attacker’s model. However, when the TEE detects that a legitimate user touched the sensor, a constant message is sent from the TEE to the main OS, which proceeds in unlocking the device. Since this message is constant (i.e., no cryptographic signature is generated by the TEE to “attest” the “unlock the device” message), an attacker that has compromised the main OS can easily spoof this message and unlock the device without having a legitimate user touching the sensor.
The primary goal of our research is to prove that many TEE features are not resistant against a kernel-level attacker. To this aim, we are planning to build a kernel module that intercepts and logs all the messages exchanged between the TEE and the main OS. These logs will then be used to study exchanged data, looking for problematic cases in a semi-automatic way. Specifically, our intuition is that problematic cases (such as the previously mentioned fingerprint-unlock functionality) can be automatically pinpointed by analysing the logs and detecting constant replies from the TEE to the OS since an attacker can easily spoof these constant replies.
We are planning to implement our logger, called **TZ Logger**, as a modular and extensible system to inspect and change the data exchanged with a TEE on-the-fly. **TZ Logger**’s design allows to adapt it to different devices and operating system versions easily. Additionally, it allows to quickly write “dissector” modules to de-serialise specific types of messages exchanged by the OS and the TEE (e.g., cryptographic-related messages, fingerprint- sensor-related messages, ...) and “patcher” modules to mutate at will exchanged messages.
We used a preliminary prototype of **TZ Logger** to successfully showcase that a kernel-level attacker can unlock a device, without having a legitimate user touching the fingerprint reader sensor and without compromising the TEE’s code
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