'faulty text' is not a correct and usable phrase in written English.
However, the phrase 'erroneous text' can be used when referring to writing that is incorrect or of poor quality. For example, "The essay was filled with erroneous text, leading to an unsatisfactory grade."
The first faulty cipher text determined eight candidates for S-box input, and the second faulty cipher text determined four candidates for S-box input.
D : denotes the faulty cipher text.
Moreover, for each faulty cipher text, exactly one bit of S 31 is randomly modified.
Normally, a faulty cipher text is taken by giving external impact on a device with voltage variation, glitch, laser, etc.
In Table4, it can be seen that given a faulty cipher text, eight candidates for S-box input with probability 5 11 have been determined or four candidates for S-box input with probability 6 11 have been determined.
If we denote by A the sets of the candidates obtained with the first faulty cipher text except the correct value of S-box input and by B the sets of the candidates obtained with the second faulty cipher text except the correct value of S-box input, we can identify the correct value with probability: P = P ( A ∩ B = ∅ ) = P ( A ∩ B = 0 ) = 16 7 × 16 − 7 3 16 7 × 16 3 ≃ 15%%.
In each specific group, the bits of faults occurred on the bits of the same nibble and the related nibble of S 31, S 31 N j, can be obtained following Algorithm 2. On the other hand, Algorithm 1 determines for each faulty cipher text, which the nibble has been corrupted.
For each faulty cipher text, we have got a difference output of the last round's S-box layer, and we can determine possible inputs of the last round's S-box layer by searching in the differences distribution table of the S-box.
Algorithm 1 arranges the faulty cipher texts and correct the cipher text in 16 groups of difference outputs of last round's S-box layer, i.e., ΔB 31 N j for 1 ≤ j ≤ 16.
However, the number of required faulty cipher texts would be increased (96 faulty cipher texts on average), but in the next section, we show an approach to obtain the master key given 18 faulty cipher texts on average.
