I am trying to find the sub keys of a FEAL-4 cipher. I am able to get a number of possibilities for $K_0$ after using Michael Stamps formula using a as a constant and going through $2^{32}$ keys. The problem is that I don't know what to do next as it isn't in any of the literature.

Stamps formula for a constant is

$$a = S23,29(L_0 \oplus R_0 \oplus L_4) \oplus S31(L_0 \oplus L_4 \oplus R_4) \oplus S31(F(L_0 \oplus R_0 \oplus K_0))$$

Looking for $K_1$ to $K_5$.

The FEAL-4 steps are:

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  • $\begingroup$ reproducing the "stamps formula" would help make this question comprehensible. $\endgroup$
    – kodlu
    Commented Dec 2, 2019 at 17:29


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