The changes in structural arrangement in transformer oil based magnetic uids upon the eect of an external magnetic eld and temperature were studied by acoustic spectroscopy. The attenuation of acoustic waves was measured as a function of an external magnetic eld in the range of 0300 mT, parallel to the direction of the eld and as a function of temperature in the range of 1535• C for various magnetic nanoparticles concentrations. The strong inuence of the steeped magnetic eld on the acoustic wave attenuation was detected and its hysteresis was observed, too. When a magnetic eld is swept at a constant rate, the dominant interactions between the external magnetic eld and the magnetic moment of the nanoparticles occur, leading to the aggregation of magnetic nanoparticles and clusters formation. However, the temperature of magnetic uids has very important inuence on the obtained dependences, where the mechanism of thermal motion acts against the cluster creation. The observed inuences of magnetic eld and temperature on the investigated magnetic liquids structure are discussed.
This work focuses on the problem of detection and prevention of stolen and misused secrets (such as private keys) for authentication toward centralized services. We propose a solution for such a problem based on the blockchain-based two-factor authentication scheme SmartOTPs, which we modify for our purposes and utilize in the setting of two and half-factor authentication against a centralized service provider. Our proposed solution consists of four entities that interact together to ensure authentication: (1) the user, (2) the authenticator, (3) the service provider, and (4) the smart contract. Out of two and a half factors of our solution, the first factor stands for the private key, and the second and a half factor stands for one-time passwords (OTPs) and their precursors, where OTPs are obtained from the precursors (a.k.a., pre-images) by cryptographically secure hashing. We describe the protocol for bootstrapping our approach as well as the authentication procedure. We make the security analysis of our solution, where on top of the main attacker model that steals secrets from the client, we analyze man-in-the-middle attacks and malware tampering with the client. In the case of stolen credentials, we show that our solution enables the user to immediately detect the attack occurrence and proceed to re-initialization with fresh credentials.
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