Example 3.3

Suppose we have the following three pairs of plaintexts and ciphertexts, where the plaintexts have the specified x-ors, that are encrypted using the same key. We use a hexadecimal representation, for brevity:

From the first pair, we compute the S-box inputs (for round 3) from Equations (3.2) and (3.3). They are:

The S-box output x-or is calculated using Equation (3.1) to be:

From the second pair, we compute the S-box inputs to be

and the S-box output x-or is

From the third pair, the S-box inputs are

and the S-box output x-or is

Next, we tabulate the values in the eight counter arrays for each of the three pairs. We illustrate the procedure with the counter array for J₁ from the first pair. In this pair, we have and . The set

Since E₁ = 000000, we have that

Hence, we increment the values 0, 7, 40, and 47 in the counter array for J₁.

The final tabulations are now presented. If we think of a bit-string of length six as being the binary representation of an integer between 0 and 63, then the 64 values correspond to the counts of 0, 1, . . . , 63. The counter arrays are as follows: