[TTPrograms]

You'll probably want to start around here: https://en.wikipedia.org/wiki/Homomorphic_encryption

[josephwegner]

See also: http://ajaxpatterns.org/Host-Proof_Hosting

[sorincos]

What I mean is that services like Wuala or Boxcryptor offer this since years. And there might be more.

[vidarh]

But homomorphic encryption is still years from being practical for pretty much anything.