355 lines
12 KiB
Python
355 lines
12 KiB
Python
# -*- coding: utf-8 -*-
|
|
#
|
|
# Signature/PKCS1_PSS.py : PKCS#1 PPS
|
|
#
|
|
# ===================================================================
|
|
# 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 digital signature protocol with appendix according to PKCS#1 PSS.
|
|
|
|
See RFC3447__ or the `original RSA Labs specification`__.
|
|
|
|
This scheme is more properly called ``RSASSA-PSS``.
|
|
|
|
For example, a sender may authenticate a message using SHA-1 and PSS like
|
|
this:
|
|
|
|
>>> from Crypto.Signature import PKCS1_PSS
|
|
>>> from Crypto.Hash import SHA
|
|
>>> from Crypto.PublicKey import RSA
|
|
>>> from Crypto import Random
|
|
>>>
|
|
>>> message = 'To be signed'
|
|
>>> key = RSA.importKey(open('privkey.der').read())
|
|
>>> h = SHA.new()
|
|
>>> h.update(message)
|
|
>>> signer = PKCS1_PSS.new(key)
|
|
>>> signature = PKCS1_PSS.sign(key)
|
|
|
|
At the receiver side, verification can be done like using the public part of
|
|
the RSA key:
|
|
|
|
>>> key = RSA.importKey(open('pubkey.der').read())
|
|
>>> h = SHA.new()
|
|
>>> h.update(message)
|
|
>>> verifier = PKCS1_PSS.new(key)
|
|
>>> if verifier.verify(h, signature):
|
|
>>> print "The signature is authentic."
|
|
>>> else:
|
|
>>> print "The signature is not authentic."
|
|
|
|
:undocumented: __revision__, __package__
|
|
|
|
.. __: http://www.ietf.org/rfc/rfc3447.txt
|
|
.. __: http://www.rsa.com/rsalabs/node.asp?id=2125
|
|
"""
|
|
|
|
# Allow nested scopes in Python 2.1
|
|
# See http://oreilly.com/pub/a/python/2001/04/19/pythonnews.html
|
|
|
|
|
|
__revision__ = "$Id$"
|
|
__all__ = [ 'new', 'PSS_SigScheme' ]
|
|
|
|
from Crypto.Util.py3compat import *
|
|
if sys.version_info[0] == 2 and sys.version_info[1] == 1:
|
|
from Crypto.Util.py21compat import *
|
|
import Crypto.Util.number
|
|
from Crypto.Util.number import ceil_shift, ceil_div, long_to_bytes
|
|
from Crypto.Util.strxor import strxor
|
|
|
|
class PSS_SigScheme:
|
|
"""This signature scheme can perform PKCS#1 PSS RSA signature or verification."""
|
|
|
|
def __init__(self, key, mgfunc, saltLen):
|
|
"""Initialize this PKCS#1 PSS signature scheme object.
|
|
|
|
:Parameters:
|
|
key : an RSA key object
|
|
If a private half is given, both signature and verification are possible.
|
|
If a public half is given, only verification is possible.
|
|
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.
|
|
saltLen : int
|
|
Length of the salt, in bytes.
|
|
"""
|
|
self._key = key
|
|
self._saltLen = saltLen
|
|
self._mgfunc = mgfunc
|
|
|
|
def can_sign(self):
|
|
"""Return True if this cipher object can be used for signing messages."""
|
|
return self._key.has_private()
|
|
|
|
def sign(self, mhash):
|
|
"""Produce the PKCS#1 PSS signature of a message.
|
|
|
|
This function is named ``RSASSA-PSS-SIGN``, and is specified in
|
|
section 8.1.1 of RFC3447.
|
|
|
|
:Parameters:
|
|
mhash : hash object
|
|
The hash that was carried out over the message. This is an object
|
|
belonging to the `Crypto.Hash` module.
|
|
|
|
:Return: The PSS signature encoded as a string.
|
|
:Raise ValueError:
|
|
If the RSA key length is not sufficiently long to deal with the given
|
|
hash algorithm.
|
|
:Raise TypeError:
|
|
If the RSA key has no private half.
|
|
|
|
:attention: Modify the salt length and the mask generation function only
|
|
if you know what you are doing.
|
|
The receiver must use the same parameters too.
|
|
"""
|
|
# TODO: Verify the key is RSA
|
|
|
|
randfunc = self._key._randfunc
|
|
|
|
# Set defaults for salt length and mask generation function
|
|
if self._saltLen == None:
|
|
sLen = mhash.digest_size
|
|
else:
|
|
sLen = self._saltLen
|
|
if self._mgfunc:
|
|
mgf = self._mgfunc
|
|
else:
|
|
mgf = lambda x,y: MGF1(x,y,mhash)
|
|
|
|
modBits = Crypto.Util.number.size(self._key.n)
|
|
|
|
# See 8.1.1 in RFC3447
|
|
k = ceil_div(modBits,8) # Convert from bits to bytes
|
|
# Step 1
|
|
em = EMSA_PSS_ENCODE(mhash, modBits-1, randfunc, mgf, sLen)
|
|
# Step 2a (OS2IP) and 2b (RSASP1)
|
|
m = self._key.decrypt(em)
|
|
# Step 2c (I2OSP)
|
|
S = bchr(0x00)*(k-len(m)) + m
|
|
return S
|
|
|
|
def verify(self, mhash, S):
|
|
"""Verify that a certain PKCS#1 PSS signature is authentic.
|
|
|
|
This function checks if the party holding the private half of the given
|
|
RSA key has really signed the message.
|
|
|
|
This function is called ``RSASSA-PSS-VERIFY``, and is specified in section
|
|
8.1.2 of RFC3447.
|
|
|
|
:Parameters:
|
|
mhash : hash object
|
|
The hash that was carried out over the message. This is an object
|
|
belonging to the `Crypto.Hash` module.
|
|
S : string
|
|
The signature that needs to be validated.
|
|
|
|
:Return: True if verification is correct. False otherwise.
|
|
"""
|
|
# TODO: Verify the key is RSA
|
|
|
|
# Set defaults for salt length and mask generation function
|
|
if self._saltLen == None:
|
|
sLen = mhash.digest_size
|
|
else:
|
|
sLen = self._saltLen
|
|
if self._mgfunc:
|
|
mgf = self._mgfunc
|
|
else:
|
|
mgf = lambda x,y: MGF1(x,y,mhash)
|
|
|
|
modBits = Crypto.Util.number.size(self._key.n)
|
|
|
|
# See 8.1.2 in RFC3447
|
|
k = ceil_div(modBits,8) # Convert from bits to bytes
|
|
# Step 1
|
|
if len(S) != k:
|
|
return False
|
|
# Step 2a (O2SIP), 2b (RSAVP1), and partially 2c (I2OSP)
|
|
# Note that signature must be smaller than the module
|
|
# but RSA.py won't complain about it.
|
|
# TODO: Fix RSA object; don't do it here.
|
|
em = self._key.encrypt(S, 0)[0]
|
|
# Step 2c
|
|
emLen = ceil_div(modBits-1,8)
|
|
em = bchr(0x00)*(emLen-len(em)) + em
|
|
# Step 3
|
|
try:
|
|
result = EMSA_PSS_VERIFY(mhash, em, modBits-1, mgf, sLen)
|
|
except ValueError:
|
|
return False
|
|
# Step 4
|
|
return result
|
|
|
|
def MGF1(mgfSeed, maskLen, hash):
|
|
"""Mask Generation Function, described in B.2.1"""
|
|
T = b("")
|
|
for counter in range(ceil_div(maskLen, hash.digest_size)):
|
|
c = long_to_bytes(counter, 4)
|
|
T = T + hash.new(mgfSeed + c).digest()
|
|
assert(len(T)>=maskLen)
|
|
return T[:maskLen]
|
|
|
|
def EMSA_PSS_ENCODE(mhash, emBits, randFunc, mgf, sLen):
|
|
"""
|
|
Implement the ``EMSA-PSS-ENCODE`` function, as defined
|
|
in PKCS#1 v2.1 (RFC3447, 9.1.1).
|
|
|
|
The original ``EMSA-PSS-ENCODE`` actually accepts the message ``M`` as input,
|
|
and hash it internally. Here, we expect that the message has already
|
|
been hashed instead.
|
|
|
|
:Parameters:
|
|
mhash : hash object
|
|
The hash object that holds the digest of the message being signed.
|
|
emBits : int
|
|
Maximum length of the final encoding, in bits.
|
|
randFunc : callable
|
|
An RNG function that accepts as only parameter an int, and returns
|
|
a string of random bytes, to be used as salt.
|
|
mgf : 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.
|
|
sLen : int
|
|
Length of the salt, in bytes.
|
|
|
|
:Return: An ``emLen`` byte long string that encodes the hash
|
|
(with ``emLen = \ceil(emBits/8)``).
|
|
|
|
:Raise ValueError:
|
|
When digest or salt length are too big.
|
|
"""
|
|
|
|
emLen = ceil_div(emBits,8)
|
|
|
|
# Bitmask of digits that fill up
|
|
lmask = 0
|
|
for i in range(8*emLen-emBits):
|
|
lmask = lmask>>1 | 0x80
|
|
|
|
# Step 1 and 2 have been already done
|
|
# Step 3
|
|
if emLen < mhash.digest_size+sLen+2:
|
|
raise ValueError("Digest or salt length are too long for given key size.")
|
|
# Step 4
|
|
salt = b("")
|
|
if randFunc and sLen>0:
|
|
salt = randFunc(sLen)
|
|
# Step 5 and 6
|
|
h = mhash.new(bchr(0x00)*8 + mhash.digest() + salt)
|
|
# Step 7 and 8
|
|
db = bchr(0x00)*(emLen-sLen-mhash.digest_size-2) + bchr(0x01) + salt
|
|
# Step 9
|
|
dbMask = mgf(h.digest(), emLen-mhash.digest_size-1)
|
|
# Step 10
|
|
maskedDB = strxor(db,dbMask)
|
|
# Step 11
|
|
maskedDB = bchr(bord(maskedDB[0]) & ~lmask) + maskedDB[1:]
|
|
# Step 12
|
|
em = maskedDB + h.digest() + bchr(0xBC)
|
|
return em
|
|
|
|
def EMSA_PSS_VERIFY(mhash, em, emBits, mgf, sLen):
|
|
"""
|
|
Implement the ``EMSA-PSS-VERIFY`` function, as defined
|
|
in PKCS#1 v2.1 (RFC3447, 9.1.2).
|
|
|
|
``EMSA-PSS-VERIFY`` actually accepts the message ``M`` as input,
|
|
and hash it internally. Here, we expect that the message has already
|
|
been hashed instead.
|
|
|
|
:Parameters:
|
|
mhash : hash object
|
|
The hash object that holds the digest of the message to be verified.
|
|
em : string
|
|
The signature to verify, therefore proving that the sender really signed
|
|
the message that was received.
|
|
emBits : int
|
|
Length of the final encoding (em), in bits.
|
|
mgf : 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.
|
|
sLen : int
|
|
Length of the salt, in bytes.
|
|
|
|
:Return: 0 if the encoding is consistent, 1 if it is inconsistent.
|
|
|
|
:Raise ValueError:
|
|
When digest or salt length are too big.
|
|
"""
|
|
|
|
emLen = ceil_div(emBits,8)
|
|
|
|
# Bitmask of digits that fill up
|
|
lmask = 0
|
|
for i in range(8*emLen-emBits):
|
|
lmask = lmask>>1 | 0x80
|
|
|
|
# Step 1 and 2 have been already done
|
|
# Step 3
|
|
if emLen < mhash.digest_size+sLen+2:
|
|
return False
|
|
# Step 4
|
|
if ord(em[-1:])!=0xBC:
|
|
return False
|
|
# Step 5
|
|
maskedDB = em[:emLen-mhash.digest_size-1]
|
|
h = em[emLen-mhash.digest_size-1:-1]
|
|
# Step 6
|
|
if lmask & bord(em[0]):
|
|
return False
|
|
# Step 7
|
|
dbMask = mgf(h, emLen-mhash.digest_size-1)
|
|
# Step 8
|
|
db = strxor(maskedDB, dbMask)
|
|
# Step 9
|
|
db = bchr(bord(db[0]) & ~lmask) + db[1:]
|
|
# Step 10
|
|
if not db.startswith(bchr(0x00)*(emLen-mhash.digest_size-sLen-2) + bchr(0x01)):
|
|
return False
|
|
# Step 11
|
|
salt = b("")
|
|
if sLen: salt = db[-sLen:]
|
|
# Step 12 and 13
|
|
hp = mhash.new(bchr(0x00)*8 + mhash.digest() + salt).digest()
|
|
# Step 14
|
|
if h!=hp:
|
|
return False
|
|
return True
|
|
|
|
def new(key, mgfunc=None, saltLen=None):
|
|
"""Return a signature scheme object `PSS_SigScheme` that
|
|
can be used to perform PKCS#1 PSS signature or verification.
|
|
|
|
:Parameters:
|
|
key : RSA key object
|
|
The key to use to sign or verify the message. This is a `Crypto.PublicKey.RSA` object.
|
|
Signing is only possible if *key* is a private RSA key.
|
|
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.
|
|
saltLen : int
|
|
Length of the salt, in bytes. If not specified, it matches the output
|
|
size of the hash function.
|
|
|
|
"""
|
|
return PSS_SigScheme(key, mgfunc, saltLen)
|
|
|