Cryptography and security are among the most important topics in computer and communication science. Still, current approaches in the field have some inherent weaknesses: Firstly, they are based on unproven mathematical assumptions, which are endangered by new algorithms or new hardware such as quantum computers. Secondly, they are built on the concept of a secret binary key (=a secret binary number), which must be known to the legitimate parties only. However, a binary key – just like any bitstring – may be cloned, extracted from mobile environments or transferred from computer systems. These facts can lead to full security breaks and restrict both the security and applicability of existing concepts.
This project deals with an alternative approach called physical cryptography, which is based on the inherent complexity of nanoscale electronic and photonic systems. The key idea of the project is to use nanostructures with specifically designed properties in order to replace or complement standard cryptoschemes and standard binary keys. This can result in strong security advantages and enables new types of applications.
One conceptually simple example is the forgery-proof labeling of valuable consumer goods, passports, banknotes or other items. Due to natural production irregularities, many physical structures have unique and non-reproducible features on a nanoscale level (see figure), which even cannot be reproduced by their original manufacturer. This makes them in principle applicable as highly secure markers or “labels”, whose security properties against reproduction excel those of standard approaches like holograms or RFID-chips storing secret keys.
Before this concept can be implemented on large scales, however, the scientific challenge consists of devising nanostructures which are at the same time very hard to replicate, inexpensive, and whose unique features can be measured simply and efficiently. The labeling problem has an extraordinary economic and political relevance: The worldwide economic damage caused by counterfeit brand products amounts to over 400 billion Dollars per year.
Further applications of physical cryptography include important security problems such as encryption, secure key exchange, hardware protection against tampering, and secure identification over insecure networks. In each of these cases, suitably designed complex nanostructures can enhance both security and practicability, while cutting on costs. Our vision is that through our newly developed concepts it will eventually be possible to make the resulting security advantages available to a broad range of users.