You should never lie to a border agent about whether you or your friend can decrypt a device. You can decline to answer any question, and you do NOT have to provide passwords or keys. Only a judge can compell you to decrypt your drive. That said, border agents can make your life miserable so it's advisable to avoid confrontation.

This advice is based on the EFF document. IANAL.

https://www.eff.org/document/defending-privacy-us-border-gui...