For some reason, the government did not appear to make the argument invited by the Supreme Court by its rulings in the FedEx and dog-sniff cases. The government could have argued that -- if the EnCase scan for a particular MD5 hash matches -- that the search is constitutionally permissible without a warrant because it revealed nothing except the existence of contraband. And, because there is no reasonable expectation of privacy in contraband, the government might argue, a search which only reveals the existence of contraband invades no legitimate privacy right.
In the Crist case, however, the court never addressed that critical issue, because it never had to. The government merely argued that an automated search was no search at all.
This unanswered question -- whether a scan of hash values looking for contraband is a permissible search -- is really the rub.
If the government may conduct warrantless searches as long as they only reveal the presence of contraband, then they could lawfully put automated sniffers on any computer, searching for the presence of files for which the MD5 hash matched that of contraband. While the software categorizing the files might be considered to be conducting a search -- and I think it is -- the contents of this search are not revealed unless the program believes it is contraband.
... ... How did I not see this earlier? Pretty sure this is the same guy writing about how data stored "in the cloud" can be legally searched without a warrant because you have involved a 3rd party who can consent to the search.
And don't think about kiddie porn. Think about the MPAA.
This is a HUGE question that will be one of the defining civil liberties battles of the next decade. I wrote about this case here.
The bottom line becomes, any technology that we can develop to collect information about crimes is A-OK so long as it never provides any information to a human being unless an actual crime has been committed...
Eventually in the distant future, you reach a point... where you've replaced your human police officers with robots... These robots are artificially intelligent and never report the results of their investigations to humans unless a crime has been committed.
Under this analysis I cannot see how the Constitution would prohibit these robots from doing all of the tyrannical things that the 4th amendment was intended to prevent the police from doing, and I don't see how this state of affairs would be materially different from not having any 4th amendment at all.
Therefore, if the 4th amendment is to have any meaning at all, there must be some reason that this kind of automated search is not reasonable.
Scalia offered the following in reference to Caballes: "This is not a new technology. This is a dog." I find that explanation extremely unsatisfying.
Its not a 'Search.' Its just a search.