Security goals

  • Client-side encryption: Before any data is synced to the cloud, it should be encrypted on the client device.
  • Encrypted local storage: Any data cached in the client should be stored in an encrypted format.
  • Resistant to offline attacks: Data stored on the server should be highly resistant to offline attacks (i.e. an attacker with a static copy of data stored on the server would have a very hard time discerning much from the data).
  • Resistant to online attacks: Analysis of storing and retrieving data should not leak potentially sensitive information.
  • Resistance to data tampering: The server should not be able to provide the client with old or bogus data for a document.

Synchronization goals

  • Consistency: multiple clients should all get sync’ed with the same data.
  • Selective sync: the ability to partially sync data. For example, so a mobile device doesn’t need to sync all email attachments.
  • Multi-platform: supports both desktop and mobile clients.
  • Quota: the ability to identify how much storage space a user is taking up.
  • Scalable cloud: distributed master-less storage on the cloud side, with no single point of failure.
  • Conflict resolution: conflicts are flagged and handed off to the application logic to resolve. Usability goals
  • Availability: the user should always be able to access their data.
  • Recovery: there should be a mechanism for a user to recover their data should they forget their password.

Known limitations

These are currently known limitations:

  • The server knows when the contents of a document have changed.
  • There is no facility for sharing documents among multiple users.
  • Soledad is not able to prevent server from withholding new documents or new revisions of a document.
  • Deleted documents are never deleted, just emptied. Useful for security reasons, but could lead to DB bloat.


  • Soledad is not for filesystem synchronization, storage or backup. It provides an API for application code to synchronize and store arbitrary schema-less JSON documents in one big flat document database. One could model a filesystem on top of Soledad, but it would be a bad fit.
  • Soledad is not intended for decentralized peer-to-peer synchronization, although the underlying synchronization protocol does not require a server. Soledad takes a cloud approach in order to ensure that a client has quick access to an available copy of the data.