Cryptography Reference
In-Depth Information
Chapter 4
Development Milestones:
DES, RSA
You may have gained the impression so far in this topic that though they
have a very difficult task, cryptanalysts eventually have the upper hand over
cryptographers. As long as commercial programs make do with simple XOR
(i.e., the bitwise Vigenere method) or strapped-down Enigma machines, this
impression is true. But there are much better encryption methods, and their best-
known representative is the DES algorithm discussed in this chapter. Modern
algorithms and implementations should be resistant to ciphering errors like
those shown in Figure 3.1. At least plaintext attacks shouldn't have a chance.
Cryptanalyzing the methods discussed from this chapter onwards by use of a
freely available program will be an absolute exception.
Discussions about security are always somewhat speculative; some methods
can be judged only intuitively. The reason is the nature of the matter, and
what's more, we only know about the results of
public
cryptological research.
Historically, we will jump from the end of World War II to the mid-1970s,
when the emerging computer technology required good encryption algorithms
and cryptology had to come out of its dark corner. It was the beginning of public
research in this field. You will have a pretty good grasp of the significance of
this change once you've read Section 4.3.1.
First, however, we need to define a few basic terms.
