Buttercup is currently under heavy development, and updates will be pushed here very frequently. The application is currently in alpha, and should be considered unstable.
Please check buttercup-core for more information on Buttercup's core module.
Buttercup uses a delta-system to manage archive changes and save conflicts. The archive, upon saving, is encrypted with AES 256bit CBC mode with a SHA256 HMAC. Encryption is performed once the password has been salted and prepared with PBKDF2 at between 200-250k iterations.
Because security with password storage is of the utmost importance, Buttercup will remain in alpha/beta release mode until some level of professional scrutiny has occurred. It is completely possible that security-related changes will occur, but this is inevitable and we handle every question and criticism with great care when it comes to the safety of using our software.