"""
Encryption module that uses the Java Cryptography Extensions (JCE).

Note that in default installations of the Java Runtime Environment, the
maximum key length is limited to 128 bits due to US export
restrictions. This makes the generated keys incompatible with the ones
generated by pycryptopp, which has no such restrictions. To fix this,
download the "Unlimited Strength Jurisdiction Policy Files" from Sun,
which will allow encryption using 256 bit AES keys.
"""
from warnings import warn

from javax.crypto import Cipher
from javax.crypto.spec import SecretKeySpec, IvParameterSpec

import jarray

# Initialization vector filled with zeros
_iv = IvParameterSpec(jarray.zeros(16, 'b'))


def aesEncrypt(data, key):
    cipher = Cipher.getInstance('AES/CTR/NoPadding')
    skeySpec = SecretKeySpec(key, 'AES')
    cipher.init(Cipher.ENCRYPT_MODE, skeySpec, _iv)
    return cipher.doFinal(data).tostring()

# magic.
aesDecrypt = aesEncrypt

has_aes = True

def getKeyLength():
    maxlen = Cipher.getMaxAllowedKeyLength('AES/CTR/NoPadding')
    return min(maxlen, 256) / 8


if getKeyLength() < 32:
    warn('Crypto implementation only supports key lengths up to %d bits. '
         'Generated session cookies may be incompatible with other '
         'environments' % (getKeyLength() * 8))