It may be useful to know if a 'Desktop' 'File' has changed since some user determined epoch. Such info could readily reside in the Database store, especially if the File key were a 'URL' attribute.
This could be provided by a subset of the OpenSSL lib which is readily available for all of the architectures presently being managed by the Gears project. A 'digest' blob attribute could be added to the 'File' class. While a 'digest' bool attribute could be added to 'OpenFileOptions'. A default 'OpenFileOptions.digest' value of false would mean no digest would be calculated for a 'selected' File. But, a 'OpenFileOptions.digest' of true would mean that a 'File.digest', e.g., SHA256, would be provided in the 'File' 'digest' blob attribute. This may require the need for a new Desktop API 'Digest' class to allow for choice of the several message digests functions provided by OpenSSL.
