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# Copyright 2018 Google LLC

#

# Use of this source code is governed by an MIT-style

# license that can be found in the LICENSE file or at

# https://opensource.org/licenses/MIT.

import latindance

class XConstruct(latindance.Latinlike):

def __init__(self, delegate):

self._delegate = delegate

self._key = None

def name(self):

return "X" + self._delegate.name()

def variant_name(self):

return "X" + self._delegate.variant_name()

def variants(self):

d = self._delegate.copy()

for v in d.variants():

d.variant = v

dhl = d.hash_lengths()

dl = d.lengths()

# "Extending the Salsa20 nonce" asserts that Salsa20 takes a 256-bit key, and

# doesn't specify how a 128-bit key would be handled, so we simply force the

# key size to be the same as the hash output length here.

if dhl["output"] == dl["key"]:

yield {"cipher": self.name(), "rounds": v["rounds"],

"delgatevariant": v, "lengths": {

"key": dhl["key"], "nonce": dhl["nonceoffset"] + dl["nonce"]}}

def _setup_variant(self):

self._delegate.variant = self.variant["delgatevariant"]

def gen_output(self, key, nonce, offset):

ks = self._delegate.copy()

nl = ks.hash_lengths()["nonceoffset"]

subkey = ks.hash(key=key, nonceoffset=nonce[:nl])

return self._delegate.gen_output(key=subkey, nonce=nonce[nl:], offset=offset)