Cryptography Reference
In-Depth Information
Chapter 20
Conclusions
In this topic, we overviewed, discussed, and put into perspective many cryptographic
systems in use today. In doing so, we made a distinction between the following three
classes of cryptosystems:
•
Unkeyed cryptosystems (see Definition 1.5);
•
Secret key cryptosystems (see Definition 1.6);
•
Public key cryptosystem (see Definition 1.7).
We also noted that this distinction is somehow arbitrary and that other classi-
fication schemes may be used instead. Nevertheless, we think that the classification
scheme is still useful and appropriate (especially for educational purposes). We reuse
it in this chapter to provide some conclusions.
20.1
UNKEYED CRYPTOSYSTEMS
Unkeyed cryptosystems play a fundamental role in contemporary cryptography and
are used in many higher level cryptographic systems and applications. In Part II of
the topic, we had a closer look at one-way functions, cryptographic hash functions,
and random bit generators.
•
One-way functions (and trapdoor functions) are at the core of modern cryp-
tography. This may come as a surprise, especially if one considers the fact
that no function has been shown to be one way in a mathematically strong
sense and that even the existence of one-way functions has not been proven so
far. In fact, there are only a few candidate one-way functions (i.e., functions
