IceDrive is a bit different. IceDrive uses the TwoFish algorithm by Bruce Schneier and also the encryption process is handled entirely client-side - meaning all data is encrypted on your device before being sent to their servers for storage. This is what's called Zero-Knowledge and only you can view and decrypt it.
The first stage is the encryption of the filename. This is done using your key to produce an encrypted hex string to store in their database. The second stage is the file is split into small, manageable chunks.
Each chunk is encrypted through 16 rounds using your 256-bit key which is stored client-side only. The small chunks are then uploaded piece by piece to their secure servers over HTTPS which are then added piece by piece to the encrypted data. The final chunk gets padded with dummy data in order to fill the twofish block size.