This change adds support for nameio/stream mode of filename encryption.
Also as a bonus change it fixes the MAC computation for volumes that
do not use chained name IV.
Remove hardcoded 32-byte volume key size in EncFSCrypto.decryptVolumeKey
to support volumes with key sizes different than 256 bits. Tested to
work fine with the standard options under encfs 1.7.4 which creates
a volume with a 192-bit key.
Added constructors for EncFSVolume to allow the password-based key
and IV data to be cached, and re-used to create an EncFSVolume for
the same volume at a later time.
On some runtimes the readBlock() implementation ended up recursively
calling into read(byte[]) since the call into super.read(byte[]) gets
reflected back into EncFSFileInputStream resulting into infinite
recursion. As a lame solution, removing read(byte[], int, int) from
EncFSFileInputStream and calling FileInputStream.read(byte[], int, int)
from readBlock().
Bundle Robert Harder's Base64 implementation [1] instead of using
javax.xml.bind.DatatypeConverter to do base64 decoding since
Android doesn't package JAXB.
[1] http://iharder.sourceforge.net/current/index.html
