Score:2

PRF with one value changed

kz flag

I'm having problem proving the following, I intuitively think this is correct but can't formally prove why.

given a PRF $F_k(x)$

proove that the following is also a PRF

$$ F'_k(x) = \begin{cases} F_k(x)&\text{if }k\neq0\\ \\\text{const(some const value)}&\text{if }k=0 \end{cases} $$


I found my mistake, I did not use the probability axioms correctly here is the full solution

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fgrieu avatar
ng flag
Hint: you are correct. Prove it by showing that any algorithm that distinguish $F'$ from random with non-vanishing advantage can be turned into (or is) one that distinguish $F$ from random with non-vanishing advantage.
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