FWIW: tarsnap is also rsync for cloud storage and Colin (guy who founded and runs tarsnap) also has won a putnam award for his work in mathematics and crypto.
>> Colin (guy who founded and runs tarsnap) also has won a putnam award for his work in mathematics and crypto.
Colin won the Putnam as an undergraduate student. The Putnam award is not a mathematics research award like the Fields Medal or the Abel Prize. It's a mathematics competition. As such, Colin didn't win the award for any particular work.
It's still quite impressive though. I would say Colin's work developing scrypt has more applicability to cryptography than his Putnam award.
I don't think they're comparable. Rclone is rsync for a variety of cloud storages while tarsnap is rsync for the tarsnap service.
That's like saying the Google Drive client or the Dropbox client are "rsync for cloud storage" just because they incrementally add changes to a cloud service.
How about if a single byte changes? Now the encrypted output looks 100% unique, and you have to treat it as an entirely new file. You lose the ability to do diffs on a file by file basis or proper deduplication across all files.
If you don't CBC, wherever is on the cloud side will have two files with one block off. Let's assume the file is a txt file. For smaller cipher block sizes, it is becoming very easy to guess your encryption key.
Tldr, you want any attacker to lose any diff ability on your encrypted data.
That depends on how you're storing the files. I was really just trying to highlight that for deduplication across files you need to deduplicate before you encrypt.
It is not free as in freedom, and it's not even "open source". The license does not allow modification, nor use outside using it for tarsnap's backup service.
http://www.tarsnap.com/