Key Generation

Key Generation

Returning to Figures 3.4 and 3.5, we see that a 64-bit key is used as input to the algorithm. The bits of the key are numbered from 1 through 64; every eighth bit is ignored, as indicated by the lack of shading in Table 3.4a. The key is first subjected to a permutation governed by a table labeled Permuted Choice One (Table 3.4b). The resulting 56-bit key is then treated as two 28-bit quantities, labeled C₀ and D₀. At each round, C_i-1 and D_i-1 are separately subjected to a circular left shift, or rotation, of 1 or 2 bits, as governed by Table 3.4d. These shifted values serve as input to the next round. They also serve as input to Permuted Ch