# Functions
JointPlaintextRange is the plaintext range corresponding to the sum of all "blocks" (complete blocks).
MinUint64 returns the minimum of two uint64 values.
New returns an initialized ContentEnc instance.
ParseHeader - parse "buf" into fileHeader object.
RandomHeader - create new fileHeader object with random Id.
# Constants
CurrentVersion is the current On-Disk-Format version.
DefaultBS is the default plaintext block size.
DefaultIVBits is the default length of IV, in bits.
HeaderLen is the total header length.
# Structs
ContentEnc is used to encipher and decipher file content.
FileHeader represents the header stored on each non-empty file.
IntraBlock identifies a part of a file block.