It is a crime to lie to federal agents in the course of a criminal investigation. You can avoid committing that crime by not lying to agents.
Note that this is not the same as the "if you're honest, you have nothing to hide anyway" argument in favor of mass surveillance. This is about answering a specific set of questions from a member of law enforcement in the course of a specific investigation. You always have the right to decline to answer questions under the Fifth Amendment in that situation as well (another way to avoid telling a lie). Obviously that's not true under a regime of mass surveillance, which is one of the many reasons I think mass surveillance is a bad idea and unconstitutional.
Note that this is not the same as the "if you're honest, you have nothing to hide anyway" argument in favor of mass surveillance. This is about answering a specific set of questions from a member of law enforcement in the course of a specific investigation. You always have the right to decline to answer questions under the Fifth Amendment in that situation as well (another way to avoid telling a lie). Obviously that's not true under a regime of mass surveillance, which is one of the many reasons I think mass surveillance is a bad idea and unconstitutional.