# A tight lower bound for the entropy of the XOR of two random variables

Let $U$ be the uniform random variable over $n$-bit binary strings, and let $X$ be another random variable that is dependent on $U$ and ranges over $n$-bit binary strings.

Assuming $I(X;U) \le \epsilon$, can we find a tight lower bound on $H(X \oplus U)$? For instance, can we prove something like $H(X \oplus U) \ge n - \epsilon$?

P.S.: The mutual information and entropy are denoted by $I$ and $H$, and $\oplus$ denotes the XOR operator.

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A non tight lower bound is the maximum of the entropy of the two variables. –  Thomas Ahle Jun 17 at 15:47