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# Upstream Author: Zooko O'Whielacronx <zooko@zooko.com>
#
# Copyright:
#
# You may use this package under the GNU General Public License, version
# 2 or, at your option, any later version. You may use this package
# under the Transitive Grace Period Public Licence, version 1.0 or, at
# your option, any later version. (You may choose to use this package
# under the terms of either licence, at your option.) See the file
# COPYING.TESTS for the terms of the GNU General Public License, version 2.
#
# The following licensing text applies to a subset of the Crypto++ source code
# which is included in the pycryptopp source tree under the "embeddedcryptopp"
# subdirectory. That embedded subset of the Crypto++ source code is not used
# when pycryptopp is built for Debian -- instead the --disable-embedded-cryptopp
# option to "setup.py build" is used to for pycryptopp to build against the
# system libcryptopp.
import hashlib, hmac
class HKDF(object):
def __init__(self, ikm, L, salt=None, info=None, digestmod = None):
self.ikm = ikm
self.keylen = L
if digestmod is None:
digestmod = hashlib.sha256
if callable(digestmod):
self.digest_cons = digestmod
else:
self.digest_cons = lambda d='':digestmod.new(d)
self.hashlen = len(self.digest_cons().digest())
if salt is None:
self.salt = b'\x00' * (self.hashlen)
else:
self.salt = salt
self.info = info or b''
#extract PRK
def extract(self):
h = hmac.new(self.salt, self.ikm, self.digest_cons)
self.prk = h.digest()
return self.prk
#expand PRK
def expand(self):
T = b""
temp = b""
i=0x01
while len(T)<self.keylen :
msg = temp
msg += self.info
msg += bytes((i,))
h = hmac.new(self.prk, msg, self.digest_cons)
temp = h.digest()
i += 1
T += temp
self.okm = T[0:self.keylen]
return self.okm
def new(ikm, L, salt=None, info="", digestmod = None):
return HKDF(ikm, L,salt,info,digestmod)
def hkdf(ikm, length, salt=None, info=""):
hk = HKDF(ikm, length ,salt,info)
hk.extract()
return hk.expand()
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