Hot answers tagged classical-cipher
5
This is a special case of the affine cipher where $m=26$.
Let's encrypt a single letter using your $E$. Let it be m, say, which is at index 12. So, $$E(12) = (7 \cdot 12 + 10) \mod{26} = 16$$
Now if we try to use the $D$ in your question, we decrypt this as:
$$D(16) = (7 \cdot 16 - 10) \mod{26} = 24$$
which is obviously not right. The issue is that your ...
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