BlockIV returns the block IV for block number "blockNo".

Derive derives an IV from an encrypted path by hashing it with sha256.

DeriveFile derives both IVs that are needed to create a file and returns them in a container struct.

PurposeBlock0IV means the value will be used as the IV of ciphertext block #0.

PurposeDirIV means the value will be used as a directory IV.

PurposeFileID means the value will be used as the file ID in the file header.

PurposeSymlinkIV means the value will be used as the IV for symlink encryption.

FileIVs contains both IVs that are needed to create a file.

Purpose identifies for which purpose the IV will be used.