[sempron64]

Clearly they have a heuristic for identifying pornographic videos that they have enough confidence in to use on what very well might be irreplaceable footage that is not pornographic and/or does not violate ToS. I can assume that they can find something similar to identify encrypted content, perhaps simply by identifying files of unknown format with high entropy. Short of steganography, which is inefficient, I don't think you can prevent Google from knowing you're storing encrypted files.