Final answer:
To find the total bias for a linear trail with three active S-boxes, calculate the bias for each S-box and sum them up. The number of active S-boxes is three. The input sum pairs are (c, 2), (2, 2), and (2, a).
Step-by-step explanation:
a. Bias of the linear trail: To find the total bias for this linear trail, we need to calculate the bias for each active S-box and then add them up. The bias of an S-box represents the difference between the probability of the input sum and the probability of the output sum. In this case, we have three active S-boxes: S2, S4, and S6. Assuming the input sum pairs are (c, 2), (2, 2), and (2, a), we can calculate the bias for each S-box and sum them up.
b. Number of active S-boxes: As mentioned before, there are three active S-boxes: S2, S4, and S6.
c. Input sum pair: The input sum pairs are (c, 2), (2, 2), and (2, a).
d. Output sum pair: Since it is not mentioned explicitly, we don't have enough information to determine the output sum pair for this linear trail.