A weak key is one where the three S-boxes are identical or nearly so. Because of the complex nonlinear key schedule, it is difficult to find weak keys. So I simulated a weak key by setting all three S-boxes to the same twisted function (rotbitcount applied to a single byte). These are exclusive-ored with 0x69 to see if the correlation at 8 bits depends on the S-box preserving the number of 1-bits.
69 6b 6d 65 ... 56 97 16 96 |
