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blinding.py
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blinding.py
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__copyright__ = """
Copyright (C) Timo Engel (timo-e@freenet.de), Berlin 2012.
This program was written as part of a master thesis advised by
Prof. Dr. Ruediger Weis at the Beuth University of Applied
Sciences Berlin.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
"""
from OpenPGP import *
import crypto
import encoding
# ------------------------------------------------------------------------------
def _randomTime(start, end):
random = crypto.randomInt(end.value - start.value)
return elements.TimeElement(start.value + random)
# ------------------------------------------------------------------------------
def _prepareSignature(hashAlgorithm, sigTime, sigKeyid):
sigPacket = packets.SignaturePacket()
sigPacket.pubAlgorithm = elements.ScalarElement(packets.ALGORITHM_RSA)
sigPacket.hashAlgorithm = elements.ScalarElement(hashAlgorithm)
sigPacket.hashedSubpackets.add(
subpackets.CreationTimeSubpacket(sigTime))
sigPacket.subpackets.add(subpackets.IssuerSubpacket(sigKeyid))
return sigPacket
# ------------------------------------------------------------------------------
def blind(publicKey, sigTime, data):
keyID = publicKey.packets[TAG_PUBKEY].keyID()
n = publicKey.packets[TAG_PUBKEY].n
e = publicKey.packets[TAG_PUBKEY].e
if sigTime is None:
sigTime = _randomTime(publicKey.creationTime(),
publicKey.expirationTime())
sigPacket = _prepareSignature(crypto.HASH_SHA256, sigTime, keyID)
sigdata = (data + sigPacket.hashdata())
plainhash = crypto.hash(sigdata, sigPacket.hashAlgorithm.value)
codedhash = encoding.pkcs15(plainhash, n.bits(),
sigPacket.hashAlgorithm.value)
m = elements.ScalarElement(codedhash).value
while True:
r = elements.ScalarElement(crypto.randomBytes(n.octets())).value
if (r > 1 and
r < n.value and
crypto.gcd(n.value, r) == 1):
break
packet = packets.BlindMessagePacket()
packet.m = elements.MPIElement(crypto.rsaBlind(m, r, e.value, n.value))
return r, plainhash[0:2], sigTime, messages.BlindMessageMessage.fromPackets((packet,))
# ------------------------------------------------------------------------------
def unblind(publicKey, sigTime, r, hashTwo, blindsig):
keyID = publicKey.packets[TAG_PUBKEY].keyID()
n = publicKey.packets[TAG_PUBKEY].n
e = publicKey.packets[TAG_PUBKEY].e
bs = blindsig.packets[TAG_BLINDSIG].s.value
s = crypto.rsaUnblind(r, n.value, bs)
sigPacket = _prepareSignature(crypto.HASH_SHA256, sigTime, keyID)
sigPacket.hashLeftTwo = hashTwo
sigPacket.sig = elements.MPIElement(s)
return messages.SignatureMessage().fromPackets((sigPacket,))
# ------------------------------------------------------------------------------