Yes, and this already exists. It's called "plausible deniability". Truecrypt has it. You can use one password and unlock the harmless data. And nobody can prove

Yes, and this already exists. It's called "plausible deniability". Truecrypt has it. You can use one password and unlock the harmless data. And nobody can prove that there is another hidden, evil, volume in there, which can only be unlocked with another password. That's the beauty of math. Sorry police!