Computer Security and Cryptography

1.12 WARNING!

The Surgeon General has determined that large key spaces may not truly protect you data!

Several examples may illustrate this point.

1. The mechanical ciphering machine invented by Alexander von Kryha in 1924 received the Prize of the Prussian Ministry of the Interior at the 1926 Police Fair and a Diploma from the famous postwar Chancellor of Germany, Konrad Adenauer, at the International Press Exhibition in Cologne two year later. Von Kryha was not only an inventor, but also an astute entrepreneur. To promote his commercial venture Internationale Kryha Machinen Gesellschaft of Hamburg, Kryha turned to the famous mathematician Georg Hamel for an endorsement. Hamel calculated the size of the key space to be 4.57 × 10⁵⁰ and concluded that only immortals could cryptanalyze Kryha ciphertext. Not withstanding Hamel's estimate, a cryptanalysis of the Kryha machine by Friedman did not require as much time and is described in the “2 Hours, 41 Minutes,” a chapter in Machine Cryptography and Modern Cryptanalysis [Devoirs and Ruth, 1985].
2. A U.S. patent [Merkle and Hellman, 1980] accompanied the publication Deavours and Kruh [1985] of the paper by Merkle and Hellman [1978] announcing the first public key cryptosystem (Chapter 10). The inventors wrote in the description of the preferred embodiment of the '582 patent

   But, the eavesdropper trapdoor knapsack problem can be made computationally infeasible to solve, thereby preventing the eavesdropper from recovering the plaintext ...