[rednaught]

In addition to Wuala, Spideroak does this as well.

A problem remains "with full security" in that you have no idea what's going on in the binary client program. Reveal or open-source the client program and allow customers who need this end-to-end security to compile the program themselves.

[SODaniel]

We at SpiderOak in fact do not cross-account deduplicate AT ALL and provide a full zero-knowledge environment with no access to client side encryption key info.

We feel that the possible cost savings involved with deduplicating data across user accounts is just not worth the inherent security risks.