262 lines
9.3 KiB
Python
262 lines
9.3 KiB
Python
|
# -*- coding: utf-8 -*-
|
||
|
|
#
|
||
|
|
# Cipher/PKCS1_OAEP.py : PKCS#1 OAEP
|
||
|
|
#
|
||
|
|
# ===================================================================
|
||
|
|
# The contents of this file are dedicated to the public domain. To
|
||
|
|
# the extent that dedication to the public domain is not available,
|
||
|
|
# everyone is granted a worldwide, perpetual, royalty-free,
|
||
|
|
# non-exclusive license to exercise all rights associated with the
|
||
|
|
# contents of this file for any purpose whatsoever.
|
||
|
|
# No rights are reserved.
|
||
|
|
#
|
||
|
|
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
|
||
|
|
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
|
||
|
|
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
|
||
|
|
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
|
||
|
|
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
|
||
|
|
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
|
||
|
|
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
|
||
|
|
# SOFTWARE.
|
||
|
|
# ===================================================================
|
||
|
|
|
||
|
|
"""RSA encryption protocol according to PKCS#1 OAEP
|
||
|
|
|
||
|
|
See RFC3447__ or the `original RSA Labs specification`__ .
|
||
|
|
|
||
|
|
This scheme is more properly called ``RSAES-OAEP``.
|
||
|
|
|
||
|
|
As an example, a sender may encrypt a message in this way:
|
||
|
|
|
||
|
|
>>> from Crypto.Cipher import PKCS1_OAEP
|
||
|
|
>>> from Crypto.PublicKey import RSA
|
||
|
|
>>>
|
||
|
|
>>> message = b'To be encrypted'
|
||
|
|
>>> key = RSA.importKey(open('pubkey.der').read())
|
||
|
|
>>> cipher = PKCS1_OAEP.new(key)
|
||
|
|
>>> ciphertext = cipher.encrypt(message)
|
||
|
|
|
||
|
|
At the receiver side, decryption can be done using the private part of
|
||
|
|
the RSA key:
|
||
|
|
|
||
|
|
>>> key = RSA.importKey(open('privkey.der').read())
|
||
|
|
>>> cipher = PKCS1_OAP.new(key)
|
||
|
|
>>> message = cipher.decrypt(ciphertext)
|
||
|
|
|
||
|
|
.. __: http://www.ietf.org/rfc/rfc3447.txt
|
||
|
|
.. __: http://www.rsa.com/rsalabs/node.asp?id=2125.
|
||
|
|
"""
|
||
|
|
|
||
|
|
__all__ = [ 'new', 'PKCS1OAEP_Cipher' ]
|
||
|
|
|
||
|
|
from Crypto.Signature.pss import MGF1
|
||
|
|
import Crypto.Hash.SHA1
|
||
|
|
|
||
|
|
from Crypto.Util.py3compat import *
|
||
|
|
import Crypto.Util.number
|
||
|
|
from Crypto.Util.number import ceil_div, bytes_to_long, long_to_bytes
|
||
|
|
from Crypto.Util.strxor import strxor
|
||
|
|
from Crypto import Random
|
||
|
|
|
||
|
|
class PKCS1OAEP_Cipher:
|
||
|
|
"""This cipher can perform PKCS#1 v1.5 OAEP encryption or decryption."""
|
||
|
|
|
||
|
|
def __init__(self, key, hashAlgo, mgfunc, label, randfunc):
|
||
|
|
"""Initialize this PKCS#1 OAEP cipher object.
|
||
|
|
|
||
|
|
:Parameters:
|
||
|
|
key : an RSA key object
|
||
|
|
If a private half is given, both encryption and decryption are possible.
|
||
|
|
If a public half is given, only encryption is possible.
|
||
|
|
hashAlgo : hash object
|
||
|
|
The hash function to use. This can be a module under `Crypto.Hash`
|
||
|
|
or an existing hash object created from any of such modules. If not specified,
|
||
|
|
`Crypto.Hash.SHA1` is used.
|
||
|
|
mgfunc : callable
|
||
|
|
A mask generation function that accepts two parameters: a string to
|
||
|
|
use as seed, and the lenth of the mask to generate, in bytes.
|
||
|
|
If not specified, the standard MGF1 is used (a safe choice).
|
||
|
|
label : byte string
|
||
|
|
A label to apply to this particular encryption. If not specified,
|
||
|
|
an empty string is used. Specifying a label does not improve
|
||
|
|
security.
|
||
|
|
randfunc : callable
|
||
|
|
A function that returns random bytes.
|
||
|
|
|
||
|
|
:attention: Modify the mask generation function only if you know what you are doing.
|
||
|
|
Sender and receiver must use the same one.
|
||
|
|
"""
|
||
|
|
self._key = key
|
||
|
|
|
||
|
|
if hashAlgo:
|
||
|
|
self._hashObj = hashAlgo
|
||
|
|
else:
|
||
|
|
self._hashObj = Crypto.Hash.SHA1
|
||
|
|
|
||
|
|
if mgfunc:
|
||
|
|
self._mgf = mgfunc
|
||
|
|
else:
|
||
|
|
self._mgf = lambda x,y: MGF1(x,y,self._hashObj)
|
||
|
|
|
||
|
|
self._label = label
|
||
|
|
self._randfunc = randfunc
|
||
|
|
|
||
|
|
def can_encrypt(self):
|
||
|
|
"""Return True/1 if this cipher object can be used for encryption."""
|
||
|
|
return self._key.can_encrypt()
|
||
|
|
|
||
|
|
def can_decrypt(self):
|
||
|
|
"""Return True/1 if this cipher object can be used for decryption."""
|
||
|
|
return self._key.can_decrypt()
|
||
|
|
|
||
|
|
def encrypt(self, message):
|
||
|
|
"""Produce the PKCS#1 OAEP encryption of a message.
|
||
|
|
|
||
|
|
This function is named ``RSAES-OAEP-ENCRYPT``, and is specified in
|
||
|
|
section 7.1.1 of RFC3447.
|
||
|
|
|
||
|
|
:Parameters:
|
||
|
|
message : byte string
|
||
|
|
The message to encrypt, also known as plaintext. It can be of
|
||
|
|
variable length, but not longer than the RSA modulus (in bytes)
|
||
|
|
minus 2, minus twice the hash output size.
|
||
|
|
|
||
|
|
:Return: A byte string, the ciphertext in which the message is encrypted.
|
||
|
|
It is as long as the RSA modulus (in bytes).
|
||
|
|
:Raise ValueError:
|
||
|
|
If the RSA key length is not sufficiently long to deal with the given
|
||
|
|
message.
|
||
|
|
"""
|
||
|
|
# TODO: Verify the key is RSA
|
||
|
|
|
||
|
|
# See 7.1.1 in RFC3447
|
||
|
|
modBits = Crypto.Util.number.size(self._key.n)
|
||
|
|
k = ceil_div(modBits,8) # Convert from bits to bytes
|
||
|
|
hLen = self._hashObj.digest_size
|
||
|
|
mLen = len(message)
|
||
|
|
|
||
|
|
# Step 1b
|
||
|
|
ps_len = k-mLen-2*hLen-2
|
||
|
|
if ps_len<0:
|
||
|
|
raise ValueError("Plaintext is too long.")
|
||
|
|
# Step 2a
|
||
|
|
lHash = self._hashObj.new(self._label).digest()
|
||
|
|
# Step 2b
|
||
|
|
ps = bchr(0x00)*ps_len
|
||
|
|
# Step 2c
|
||
|
|
db = lHash + ps + bchr(0x01) + message
|
||
|
|
# Step 2d
|
||
|
|
ros = self._randfunc(hLen)
|
||
|
|
# Step 2e
|
||
|
|
dbMask = self._mgf(ros, k-hLen-1)
|
||
|
|
# Step 2f
|
||
|
|
maskedDB = strxor(db, dbMask)
|
||
|
|
# Step 2g
|
||
|
|
seedMask = self._mgf(maskedDB, hLen)
|
||
|
|
# Step 2h
|
||
|
|
maskedSeed = strxor(ros, seedMask)
|
||
|
|
# Step 2i
|
||
|
|
em = bchr(0x00) + maskedSeed + maskedDB
|
||
|
|
# Step 3a (OS2IP)
|
||
|
|
em_int = bytes_to_long(em)
|
||
|
|
# Step 3b (RSAEP)
|
||
|
|
m_int = self._key._encrypt(em_int)
|
||
|
|
# Step 3c (I2OSP)
|
||
|
|
c = long_to_bytes(m_int, k)
|
||
|
|
return c
|
||
|
|
|
||
|
|
def decrypt(self, ct):
|
||
|
|
"""Decrypt a PKCS#1 OAEP ciphertext.
|
||
|
|
|
||
|
|
This function is named ``RSAES-OAEP-DECRYPT``, and is specified in
|
||
|
|
section 7.1.2 of RFC3447.
|
||
|
|
|
||
|
|
:Parameters:
|
||
|
|
ct : byte string
|
||
|
|
The ciphertext that contains the message to recover.
|
||
|
|
|
||
|
|
:Return: A byte string, the original message.
|
||
|
|
:Raise ValueError:
|
||
|
|
If the ciphertext length is incorrect, or if the decryption does not
|
||
|
|
succeed.
|
||
|
|
:Raise TypeError:
|
||
|
|
If the RSA key has no private half.
|
||
|
|
"""
|
||
|
|
|
||
|
|
# See 7.1.2 in RFC3447
|
||
|
|
modBits = Crypto.Util.number.size(self._key.n)
|
||
|
|
k = ceil_div(modBits,8) # Convert from bits to bytes
|
||
|
|
hLen = self._hashObj.digest_size
|
||
|
|
|
||
|
|
# Step 1b and 1c
|
||
|
|
if len(ct) != k or k<hLen+2:
|
||
|
|
raise ValueError("Ciphertext with incorrect length.")
|
||
|
|
# Step 2a (O2SIP)
|
||
|
|
ct_int = bytes_to_long(ct)
|
||
|
|
# Step 2b (RSADP)
|
||
|
|
m_int = self._key._decrypt(ct_int)
|
||
|
|
# Complete step 2c (I2OSP)
|
||
|
|
em = long_to_bytes(m_int, k)
|
||
|
|
# Step 3a
|
||
|
|
lHash = self._hashObj.new(self._label).digest()
|
||
|
|
# Step 3b
|
||
|
|
y = em[0]
|
||
|
|
# y must be 0, but we MUST NOT check it here in order not to
|
||
|
|
# allow attacks like Manger's (http://dl.acm.org/citation.cfm?id=704143)
|
||
|
|
maskedSeed = em[1:hLen+1]
|
||
|
|
maskedDB = em[hLen+1:]
|
||
|
|
# Step 3c
|
||
|
|
seedMask = self._mgf(maskedDB, hLen)
|
||
|
|
# Step 3d
|
||
|
|
seed = strxor(maskedSeed, seedMask)
|
||
|
|
# Step 3e
|
||
|
|
dbMask = self._mgf(seed, k-hLen-1)
|
||
|
|
# Step 3f
|
||
|
|
db = strxor(maskedDB, dbMask)
|
||
|
|
# Step 3g
|
||
|
|
valid = 1
|
||
|
|
one = db[hLen:].find(bchr(0x01))
|
||
|
|
lHash1 = db[:hLen]
|
||
|
|
if lHash1!=lHash:
|
||
|
|
valid = 0
|
||
|
|
if one<0:
|
||
|
|
valid = 0
|
||
|
|
if bord(y)!=0:
|
||
|
|
valid = 0
|
||
|
|
if not valid:
|
||
|
|
raise ValueError("Incorrect decryption.")
|
||
|
|
# Step 4
|
||
|
|
return db[hLen+one+1:]
|
||
|
|
|
||
|
|
def new(key, hashAlgo=None, mgfunc=None, label=b(''), randfunc=None):
|
||
|
|
"""Return a cipher object `PKCS1OAEP_Cipher` that can be used to perform PKCS#1 OAEP encryption or decryption.
|
||
|
|
|
||
|
|
:Parameters:
|
||
|
|
key : RSA key object
|
||
|
|
The key to use to encrypt or decrypt the message. This is a `Crypto.PublicKey.RSA` object.
|
||
|
|
Decryption is only possible if *key* is a private RSA key.
|
||
|
|
hashAlgo : hash object
|
||
|
|
The hash function to use. This can be a module under `Crypto.Hash`
|
||
|
|
or an existing hash object created from any of such modules. If not specified,
|
||
|
|
`Crypto.Hash.SHA1` is used.
|
||
|
|
mgfunc : callable
|
||
|
|
A mask generation function that accepts two parameters: a string to
|
||
|
|
use as seed, and the lenth of the mask to generate, in bytes.
|
||
|
|
If not specified, the standard MGF1 is used (a safe choice).
|
||
|
|
label : byte string
|
||
|
|
A label to apply to this particular encryption. If not specified,
|
||
|
|
an empty string is used. Specifying a label does not improve
|
||
|
|
security.
|
||
|
|
randfunc : callable
|
||
|
|
A function that returns random bytes.
|
||
|
|
The default is `Random.get_random_bytes`.
|
||
|
|
|
||
|
|
:attention: Modify the mask generation function only if you know what you are doing.
|
||
|
|
Sender and receiver must use the same one.
|
||
|
|
"""
|
||
|
|
|
||
|
|
if randfunc is None:
|
||
|
|
randfunc = Random.get_random_bytes
|
||
|
|
return PKCS1OAEP_Cipher(key, hashAlgo, mgfunc, label, randfunc)
|
||
|
|
|