In case of free xor circuit, the regular encryption is insecure since
the delta can be revealed. This was fixed now - in case of freeXor
circuit the computation was changed to multiply the input keys by 2 and
4.
1. Changed the default encryption scheme to
AESFixedKeyMultiKeyEncryption.
2. In case the encryption scheme is AESFixedKeyMultiKeyEncryption, set
the isFreeXor boolean to true in order to encrypt correctly.
Added default constructor.
1. added comments.
2. swaped the implementation for free xor circuit: instead of shifting
right k0 and shifting left k1, now shifting left k0 and shifting right
k1.
Merge pull request #28 from cryptobiu/FreeXorCircuitSecurityBug

Free xor circuit security bug