There is, however, no easily accessible public record of this having been tried in court as of May 2013 and an argument could be made that, similar to the opinion expressed by Attorney Rick G. Sanders of Aaron | Sanders PLLC in regards to the iTunes Match "Honeypot" discussion, that a warrant to search the cloud storage provider's servers would be hard to obtain without other, independent, evidence establishing probable cause for copyright infringement.
Such legal restraint would obviously not apply to the Secret Police of an oppressive government who could potentially gain access to the encrypted files through various forms of hacking or other cybercrime.