Change IV generation to match NIST spec

[bain3]

Currently IVs are encrypted with the file for redundant security. According to the NIST Special Publication 800-38D they do not need to be secret, and only require to be unique, not cryptographically random. This could allow blocks to be decrypted and handled in parallel.

[bain3]

This is a breaking change and would require to have to keep the old scheme for a while for backwards compatibility.

[practicingman]

hi, when will" encrypt(upload) & decrypt(download) be parallel" feature be available?

[bain3]

I'm not sure. It is just a new possibility that opens up. I think it will first be implemented in the native client because I feel it could get more use there, since it will probably be run on servers and desktops. Right now it is not an important feature.