This work deals with key generation based on Physically Obfuscated Keys (POKs), i.e., a certain type of tamper-evident Physical Unclonable Function (PUF) that can be used as protection against invasive physical attacks.   To design a protected device, one must take attacks such as probing of data lines or penetration of the physical security boundary into consideration. For the implementation of a POK as a countermeasure, physical properties of a material -- which covers all parts to be protected -- are measured. After measuring these properties, i.e. analog values, they have to be quantized in order to derive a cryptographic key.   This paper will present and discuss the impact of the quantization method with regard to three parameters: key quality, tamper-sensitivity, and reliability.   Our contribution is the analysis of two different quantization schemes considering these parameters. Foremost, we propose a new approach to achieve improved tamper-sensitivity in the worst-case with no information leakage. We then analyze a previous solution and compare it to our scenario. Based on empirical data we demonstrate the advantages of our approach.   This significantly improves the level of protection of a tamper-resistant cryptographic device compared to cases not benefiting from our scheme.
['Vincent Immler', 'Maxim Hennig', 'Ludwig Kürzinger', 'Georg Sigl']
Practical Aspects of Quantization and Tamper-Sensitivity for Physically Obfuscated Keys