# -*- coding: utf-8 -*-
#
# PublicKey/DSA.py : DSA signature primitive
#
# Written in 2008 by Dwayne C. Litzenberger <dlitz@dlitz.net>
#
# ===================================================================
# 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.
# ===================================================================
__all__ = ['generate', 'construct', 'DsaKey', 'import_key' ]
import binascii
import struct
import itertools
from Cryptodome.Util.py3compat import bchr, bord, tobytes, tostr, iter_range
from Cryptodome import Random
from Cryptodome.IO import PKCS8, PEM
from Cryptodome.Hash import SHA256
from Cryptodome.Util.asn1 import (
DerObject, DerSequence,
DerInteger, DerObjectId,
DerBitString,
)
from Cryptodome.Math.Numbers import Integer
from Cryptodome.Math.Primality import (test_probable_prime, COMPOSITE,
PROBABLY_PRIME)
from Cryptodome.PublicKey import (_expand_subject_public_key_info,
_create_subject_public_key_info,
_extract_subject_public_key_info)
# ; The following ASN.1 types are relevant for DSA
#
# SubjectPublicKeyInfo ::= SEQUENCE {
# algorithm AlgorithmIdentifier,
# subjectPublicKey BIT STRING
# }
#
# id-dsa ID ::= { iso(1) member-body(2) us(840) x9-57(10040) x9cm(4) 1 }
#
# ; See RFC3279
# Dss-Parms ::= SEQUENCE {
# p INTEGER,
# q INTEGER,
# g INTEGER
# }
#
# DSAPublicKey ::= INTEGER
#
# DSSPrivatKey_OpenSSL ::= SEQUENCE
# version INTEGER,
# p INTEGER,
# q INTEGER,
# g INTEGER,
# y INTEGER,
# x INTEGER
# }
#
class DsaKey(object):
r"""Class defining an actual DSA key.
Do not instantiate directly.
Use :func:`generate`, :func:`construct` or :func:`import_key` instead.
:ivar p: DSA modulus
:vartype p: integer
:ivar q: Order of the subgroup
:vartype q: integer
:ivar g: Generator
:vartype g: integer
:ivar y: Public key
:vartype y: integer
:ivar x: Private key
:vartype x: integer
"""
_keydata = ['y', 'g', 'p', 'q', 'x']
def __init__(self, key_dict):
input_set = set(key_dict.keys())
public_set = set(('y' , 'g', 'p', 'q'))
if not public_set.issubset(input_set):
raise ValueError("Some DSA components are missing = %s" %
str(public_set - input_set))
extra_set = input_set - public_set
if extra_set and extra_set != set(('x',)):
raise ValueError("Unknown DSA components = %s" %
str(extra_set - set(('x',))))
self._key = dict(key_dict)
def _sign(self, m, k):
if not self.has_private():
raise TypeError("DSA public key cannot be used for signing")
if not (1 < k < self.q):
raise ValueError("k is not between 2 and q-1")
x, q, p, g = [self._key[comp] for comp in ['x', 'q', 'p', 'g']]
blind_factor = Integer.random_range(min_inclusive=1,
max_exclusive=q)
inv_blind_k = (blind_factor * k).inverse(q)
blind_x = x * blind_factor
r = pow(g, k, p) % q # r = (g**k mod p) mod q
s = (inv_blind_k * (blind_factor * m + blind_x * r)) % q
return map(int, (r, s))
def _verify(self, m, sig):
r, s = sig
y, q, p, g = [self._key[comp] for comp in ['y', 'q', 'p', 'g']]
if not (0 < r < q) or not (0 < s < q):
return False
w = Integer(s).inverse(q)
u1 = (w * m) % q
u2 = (w * r) % q
v = (pow(g, u1, p) * pow(y, u2, p) % p) % q
return v == r
def has_private(self):
"""Whether this is a DSA private key"""
return 'x' in self._key
def can_encrypt(self): # legacy
return False
def can_sign(self): # legacy
return True
def publickey(self):
"""A matching DSA public key.
Returns:
a new :class:`DsaKey` object
"""
public_components = dict((k, self._key[k]) for k in ('y', 'g', 'p', 'q'))
return DsaKey(public_components)
def __eq__(self, other):
if bool(self.has_private()) != bool(other.has_private()):
return False
result = True
for comp in self._keydata:
result = result and (getattr(self._key, comp, None) ==
getattr(other._key, comp, None))
return result
def __ne__(self, other):
return not self.__eq__(other)
def __getstate__(self):
# DSA key is not pickable
from pickle import PicklingError
raise PicklingError
def domain(self):
"""The DSA domain parameters.
Returns
tuple : (p,q,g)
"""
return [int(self._key[comp]) for comp in ('p', 'q', 'g')]
def __repr__(self):
attrs = []
for k in self._keydata:
if k == 'p':
bits = Integer(self.p).size_in_bits()
attrs.append("p(%d)" % (bits,))
elif hasattr(self, k):
attrs.append(k)
if self.has_private():
attrs.append("private")
# PY3K: This is meant to be text, do not change to bytes (data)
return "<%s @0x%x %s>" % (self.__class__.__name__, id(self), ",".join(attrs))
def __getattr__(self, item):
try:
return int(self._key[item])
except KeyError:
raise AttributeError(item)
def export_key(self, format='PEM', pkcs8=None, passphrase=None,
protection=None, randfunc=None):
"""Export this DSA key.
Args:
format (string):
The encoding for the output:
- *'PEM'* (default). ASCII as per `RFC1421`_/ `RFC1423`_.
- *'DER'*. Binary ASN.1 encoding.
- *'OpenSSH'*. ASCII one-liner as per `RFC4253`_.
Only suitable for public keys, not for private keys.
passphrase (string):
*Private keys only*. The pass phrase to protect the output.
pkcs8 (boolean):
*Private keys only*. If ``True`` (default), the key is encoded
with `PKCS#8`_. If ``False``, it is encoded in the custom
OpenSSL/OpenSSH container.
protection (string):
*Only in combination with a pass phrase*.
The encryption scheme to use to protect the output.
If :data:`pkcs8` takes value ``True``, this is the PKCS#8
algorithm to use for deriving the secret and encrypting
the private DSA key.
For a complete list of algorithms, see :mod:`Cryptodome.IO.PKCS8`.
The default is *PBKDF2WithHMAC-SHA1AndDES-EDE3-CBC*.
If :data:`pkcs8` is ``False``, the obsolete PEM encryption scheme is
used. It is based on MD5 for key derivation, and Triple DES for
encryption. Parameter :data:`protection` is then ignored.
The combination ``format='DER'`` and ``pkcs8=False`` is not allowed
if a passphrase is present.
randfunc (callable):
A function that returns random bytes.
By default it is :func:`Cryptodome.Random.get_random_bytes`.
Returns:
byte string : the encoded key
Raises:
ValueError : when the format is unknown or when you try to encrypt a private
key with *DER* format and OpenSSL/OpenSSH.
.. warning::
If you don't provide a pass phrase, the private key will be
exported in the clear!
.. _RFC1421: http://www.ietf.org/rfc/rfc1421.txt
.. _RFC1423: http://www.ietf.org/rfc/rfc1423.txt
.. _RFC4253: http://www.ietf.org/rfc/rfc4253.txt
.. _`PKCS#8`: http://www.ietf.org/rfc/rfc5208.txt
"""
if passphrase is not None:
passphrase = tobytes(passphrase)
if randfunc is None:
randfunc = Random.get_random_bytes
if format == 'OpenSSH':
tup1 = [self._key[x].to_bytes() for x in ('p', 'q', 'g', 'y')]
def func(x):
if (bord(x[0]) & 0x80):
return bchr(0) + x
else:
return x
tup2 = [func(x) for x in tup1]
keyparts = [b'ssh-dss'] + tup2
keystring = b''.join(
[struct.pack(">I", len(kp)) + kp for kp in keyparts]
)
return b'ssh-dss ' + binascii.b2a_base64(keystring)[:-1]
# DER format is always used, even in case of PEM, which simply
# encodes it into BASE64.
params = DerSequence([self.p, self.q, self.g])
if self.has_private():
if pkcs8 is None:
pkcs8 = True
if pkcs8:
if not protection:
protection = 'PBKDF2WithHMAC-SHA1AndDES-EDE3-CBC'
private_key = DerInteger(self.x).encode()
binary_key = PKCS8.wrap(
private_key, oid, passphrase,