Coating objects with microscopic droplets of liquid crystals makes it possible to identify and authenticate objects as if they had biometric-like features: this is extremely valuable as an anti-counterfeiting measure. How to extract features from images has been studied elsewhere, but exchanging data about features is not enough if we wish to build secure cryptographic authentication protocols . What we need are authentication tokens (i.e., bitstrings), strategies to cope with noise, always present when processing images , and solutions to protect the original features so that it is impossible to reproduce them from the tokens. Secure sketches and fuzzy extractors are the cryptographic toolkits that offer these functionalities, but they must be instantiated to work with the peculiar specific features extracted from images of liquid crystals. We show how this can work and how we can obtain uniform, error-tolerant, and random strings, and how they are used to authenticate liquid crystal coated objects. Our protocol reminds an existing biometric-based protocol, but only apparently. Using the original protocol as-it-is would make the process vulnerable to an attack that exploits certain physical peculiarities of our liquid crystal coatings. Instead, our protocol is robust against the attack. We prove all our security claims formally, by modeling and verifying in Proverif, our protocol and its cryptographic schemes. We implement and benchmark our solution, measuring both the performance and the quality of authentication .

Multi-Precision Integer (MPI) arithmetic is a performance-critical component of many public-key cryptosystems, including besides classical ones (e.g., RSA, ECC) also isogeny-based post-quantum schemes. In this paper, we analyze and compare two widely-used MPI representations, namely full-radix and reduced-radix, for the efficient implementation of modular arithmetic operations on the 64-bit RISC-V (RV64GC) architecture. We also evaluate how the execution times of both can be further improved with Instruction Set Extensions (ISEs). The ISEs we propose are able to accelerate a CSIDH-512 class group action by a factor of 1.71 compared to a standard software implementation on a 64-bit Rocket core. This speed-up comes at the cost of a hardware overhead of about 10%.

Recently there has been a significant progress on the tower number field sieve (TNFS) method, reducing the complexity of the discrete logarithm problem (DLP) in finite field extensions of composite degree. These new variants of the TNFS attacks have a major impact on pairing-based cryptography and particularly on the selection of the underlying elliptic curve groups and extension fields. In this paper we revise the criteria for selecting pairing-friendly elliptic curves considering these new TNFS attacks in finite extensions of composite embedding degree. Additionally we update the criteria for finite extensions of prime degree in order to meet today's security requirements.