Читать книгу Information Security - Mark Stamp - Страница 31

In this section, we examine four classic ciphers, each of which illustrates a feature that is relevant to modern cryptosystems. First on our agenda is the simple substitution, which is one of the oldest cipher systems—dating back at least 2,000 years—and one that is good for illustrating some basic attacks. We then turn our attention to a type of double transposition cipher, which includes important concepts that are used in modern ciphers. We discuss classic codebooks, since many modern ciphers can be viewed as the “electronic″ equivalent of codebooks. We also consider the one‐time pad, a cipher that is provably secure. No other cipher in this book (or in common use) is provably secure.