That merely adds a layer of indirection rather than solving anything. It is still using the person's silence against them and saying "there is proof behind that door." If there is proof it needs to be produced. If the State can always go "well there's encrypted data and inside the encrypted data is the reason to imprison this guy." You dont need the evidence, you just need to know its not visible. Why ever even seek the decryption order if you automatically get the negative implication for free?

Its never been the defendants job to prove their innocence. Remember that's where we start. A defendant is innocent. An innocent person does not need to unlock anything, they're innocent.