Abstract
The object of this chapter is to examine some symmetric encryption schemes that are of historical interest. From this analysis it will turn out that all of them are easy to cryptanalyze. Thus their interest is not because they can be used in practice but, rather, because their cryptanalysis gives us valuable information about some kinds of attacks that have been tried and that should be prevented when designing an encryption scheme. This chapter has an introductory nature and in it we use only very basic mathematical notions, mainly from modular arithmetic, elementary probability and statistics, and linear algebra. Modular arithmetic and probability are reviewed in the next chapter in more detail than is required to understand the ciphers presented here, and we refer to that chapter for further background. At the same time, we use Maple to implement and to cryptanalyze these schemes and this also serves as an introduction to the Maple programming environment that we will be using throughout.
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Notes
- 1.
Here and in the sequel we use Maple’s notation for an integer range.
- 2.
The precise meaning of the term pseudo-random is defined in Chap. 3; for now we can informally think of pseudo-random as something that, while possibly being non-random, looks random to a computationally bounded adversary.
- 3.
Pseudo-random number generators should always be initialized—or seeded—before using them because, otherwise, the sequence of generated values will always be the same.
- 4.
DES is a private-key encryption scheme that is briefly discussed in Sect. 4.2.1.
- 5.
Of course, even if this happens, ciphertext decryption may still be possible, but not by this automated method.
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© 2013 Springer-Verlag Berlin Heidelberg
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Gómez Pardo, J.L. (2013). Classical Ciphers and Their Cryptanalysis. In: Introduction to Cryptography with Maple. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-32166-5_1
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DOI: https://doi.org/10.1007/978-3-642-32166-5_1
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