Q: Copying the initialization vector (IV) of an encryption key and the file for which it is used, is it CP infringement?

A: Reverse engineering isn't unlawful per se if the subject matter in question isn't protected by copyright or a patent, or isn't trade secret theft.

To be copyright infringement, the IV/file must be copyrightable; i.e., it must be an "original work of authorship" with a minimum amount of creativity - it can't be a mere idea or something that is so common that there are only limited ways to express it. See 17 USC 101 et al., merger doctrine, etc. And even if the work is copyrightable, a federal copyright registration will be needed to assert infringement.

If the IV/file is protected by a patent and the other company is infringing a claim of the patent with its copy, then reverse engineering might go to willfulness and treble damages.

Of course, even without copyright or patent, if the creator/author took steps to keep the IV/file secret and reverse engineering was used to break the code, so to speak, that might amount to trade secret theft or even criminal liability.

It would be prudent to discuss specific facts with an intellectual property litigation attorney to ensure all things are considered to weigh potential courses of action.

Good luck.

A: To be clear, once the IV/file was created and tangibly recorded, a "common law" copyright came into existence, again assuming that the subject matter is copyrightable. However, to stop the copying via court action, a federal copyright registration would be needed. A registration could be applied for after the fact if there wasn't one when the copying was discovered, but actual/real damages would have to be sought rather than statutory damages. See 17 USC 504.