Andreas Würfl

Alternative Approaches in Cryptography

Abstract

Several encryption algorithms have been discussed in the course of this seminar. This paper will introduce two alternative approaches. A change in the concept of provable security leads to a cipher which is shown to be "perfect with high probability". Assuming that the memory capabilities of a potential adversary are limited a strongly-randomized cipher is devised which uses a publicly-accessible string of random bits. In this cipher the secret key is short but the plaintext can be very long. The second approach is based on quantum physics. Heisenberg's uncertainty principle guarantees the security of quantum cryptography. The first experiment which demonstrated the practicability of the only known encryption unbreakable by law of nature was conducted in 1989. The physical and technical fundamentals are introduced as well as the Quantum Key Exchange (QKE) protocol. We will demonstrate the effects of attempted eavesdropping and its detection. Finally the rapid development of the last 15 years and the currently available implementations will be presented.