[SOLVED] A home made alternative to Spider Oak?

[vcmota]

I have been using spideroak-bin in gentoo for some months now and, regarding functionality, it is a perfect solution for me, offering: 1) above average security, strongly advertising of its zero knowledge policy 2) on line cloud storage and 3) real-time fast sync among several machines. However, it lacks perhaps the most important feature for a truly trustworthy platform: it is not open source. Among other things that may even implicate that at some point in the near future spideroak may be removed from the stable tree, in case that its owners stop using good coding practices (I did not take that from nowhere, right now for example there seems to be a persistent bug due exactly for this reason). Since I just cant find any open source alternative for spider oak I was planning in setting up a home made solution. So my question is: how that should looks like? I was thinking about something like this:

[1]buying cloud space in a plataform like amazon s3;
[2]implementing a tool such as Duplicity to make regulars backups from one machine to amazon s3;
[3]implementing duplicity in cron in order to sync the machines I am not using with the contents in my cloud backup.

Does it looks safe and functional? Or there are huge flaws that I did not see?

Thank you all.

[vcmota]

Just an update for whoever may be following. A little after my post SpiderOak has in fact been removed from the stable tree, as I feared. So I had to rush into choosing an alternative and that is what I picked:

1) Syncthing: a free and open source tool dedicated solely to sincronize folders between as many machines as you need. It is a decentralized solution, which does not depends at any moment of setting up a local server as is the case with seafile, owncloud, etc... It is simple and the forums are very active, in a few weeks of usage I have received fast and solid support for both issues and questions about features, including support of the developers themselves in some cases. Note that Syncthing is not designed and should not be used as a backup tool, since if a given file is deleted in one of the machines, rightfully or by accident, it will be deleted in all other machines. There is file versioning, which may help to avoid this type o accident, but bottom line is that you will also need a backup tool.
2) periodic cloud backups using duplicity: a free and open source online backup tool. Combines gpg and rsync (works with scp, sftp and other protocols as well) and can be used either for local backups or by cloud bakcup. It does incremental encrypted backup, so it is a very interesting backup utility. Since duplicity encrypts by default I picked the cheapest cloud service I could find, without worrying too much about its privacy policies;
3) periodic local backups using rsync: in addition to duplicity I am also performing periodic local backups in external hds, in the event that I may not be allowed or just became incapable of access the cloud backup for some reason.

As far as I can tell I am now using a full open source and free arrangement with reliable tools, all of which are in the gentoo stable tree. It is not as practical as SpiderOak but I my guess is that it is even more secure.