“Inauthentic” or “unauthentic”?

Which is correct?
Gray market products are either _________, distributed outside the authorized channels, or both.
a. inauthentic
b. unauthentic

Explanation:
Either word is acceptable. I prefer “inauthentic” but “unauthentic” is correct as well. The gray market is the collective system of unauthorized sales channels for products. Gray market software, for example, may be pirated.

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