> Whoever knowingly alters, destroys, mutilates, conceals, covers up, falsifies, or makes a false entry in any record, document, or tangible object with the intent to impede, obstruct, or influence the investigation or proper administration of any matter within the jurisdiction of any department or agency of the United States or any case filed under title 11, or in relation to or contemplation of any such matter or case, shall be fined under this title, imprisoned not more than 20 years, or both.

That covers the first part of my comment. As for the second part, there is 18 U.S.C. § 2232(a) (destruction or removal of property to prevent seizure)

> Whoever, before, during, or after any search for or seizure of property by any person authorized to make such search or seizure, knowingly destroys, damages, wastes, disposes of, transfers, or otherwise takes any action, or knowingly attempts to destroy, damage, waste, dispose of, transfer, or otherwise take any action, for the purpose of preventing or impairing the Government's lawful authority to take such property into its custody or control or to continue holding such property under its lawful custody and control, shall be fined under this title or imprisoned not more than 5 years, or both.

IANAL, but the encrypted data on the device can be considered property, and the act of providing the duress PIN in place of the real one can be considered a knowing action for the purpose of preventing the government either from continuing to hold that data under its control, or from seizing the data into its control in the first place (since the data was never decrypted).