The case of locks on doors is not applicable to cryptography. While it is true that a lock can represent an encryption scheme, its not applicable here.
Reason is this:
What is reasonable suspecion here? What does the officer present to the judge as reason that he or she wants the warrant to search what is inside the lock? In a typical senario, the judge would have to be presented with evidence , such as "well judge, we smelled illegal substance in some place with a lock and we need to unlock it to see where the smell comes from", or "well judge we hear a woman's voice screaming in a house that is locked, and we need a warrant to get to the bottom of this". This is reasonable, that means that the lock is only a physical lock, and not a true lock in the sense that it locks the inside from the outside (including sound,thermal etcc..(closed system)).
In the case of a file that is encrypted, there is no way an officer can "reaonably suspect" that such encrypted file has important national security information for examlple. Because he has to present to the judge something real, something tangeable for the judge to issue the warrant.
Hence its not applicable here. Because an encrypted file is a totally closed system, that does not tell what its "locking" nor hints at it, where a reasonable expectation of privacy applies.
Hence, its not applicable.
Except that doesn't hold water. Consider the usual bete noir that is used when trying to make excuses to regulate the net; child p0rn and terrorism.
So the evidence presented would be "We know user X logged onto this child p0rn swapping web site at date X, time Y from their ISP logs", or "They are known to have swapped files with known pedophile Z" or "We know they attended terrorism training camps in country I" or "They purchased materials A, B and C used in bomb making". There's your scream evidence. It's not about assuming all encyrption hides criminality as you want to argue.
It most certainly IS applicable.