1. Please implement the Simplified DES-Algorithm as shown in chapter 8.2. The implementation must be performed using C (neither C++ nor any other language).

2. After implementation you must test this algorithm. For this purpose you have to develop a test concept including at least two major parts to be tested. The test must be performed.

3. The implementation shall be used for a brute-force-attack to de-cipher an unknown text with an unknown key. As the key inside S-DES is only 10 bit long, there are only 1024 possibilities, but the decision which key is the most likely one is not easy as long as you dont know the used language. Find at least one criteria how to decide whether a key is a candidate or not, and test this for usability.

64-Bo-Klartextblock 64-Bit-Schwel In 56 Bits werden ) Fingpermutation IP R Iterationsunde 1 K R Teilschoenen LES Ilcratisnande 16 LA RA Ausgangsportation IP 64-Bit-Schleschtext-Block Figure 8.10 DES algorithm (schematic) On closer inspection, one can see the parallels to the S-DES: Similar algorithms are executed here, but with different parameters. Table 8.1 summarizes the parameters, Table 8.1: Comparison parameters S-DES and DES Parameter S-DES DES Key length 10 bit 56 bit Number of partial keys (length) 2 (8 bit) 16 (48) Block length paintext 8 bit 64 bit Number of iterations 2 2 16