/opt/alt/python27/lib64/python2.7/site-packages/Crypto/PublicKey
Edit: /opt/alt/python27/lib64/python2.7/site-packages/Crypto/PublicKey/DSA.py (13695B)
# -*- coding: utf-8 -*-
#
# PublicKey/DSA.py : DSA signature primitive
#
# Written in 2008 by Dwayne C. Litzenberger
#
# ===================================================================
# 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.
# ===================================================================
"""DSA public-key signature algorithm.
DSA_ is a widespread public-key signature algorithm. Its security is
based on the discrete logarithm problem (DLP_). Given a cyclic
group, a generator *g*, and an element *h*, it is hard
to find an integer *x* such that *g^x = h*. The problem is believed
to be difficult, and it has been proved such (and therefore secure) for
more than 30 years.
The group is actually a sub-group over the integers modulo *p*, with *p* prime.
The sub-group order is *q*, which is prime too; it always holds that *(p-1)* is a multiple of *q*.
The cryptographic strength is linked to the magnitude of *p* and *q*.
The signer holds a value *x* (*0>> from Crypto.Random import random
>>> from Crypto.PublicKey import DSA
>>> from Crypto.Hash import SHA
>>>
>>> message = "Hello"
>>> key = DSA.generate(1024)
>>> h = SHA.new(message).digest()
>>> k = random.StrongRandom().randint(1,key.q-1)
>>> sig = key.sign(h,k)
>>> ...
>>> if key.verify(h,sig):
>>> print "OK"
>>> else:
>>> print "Incorrect signature"
.. _DSA: http://en.wikipedia.org/wiki/Digital_Signature_Algorithm
.. _DLP: http://www.cosic.esat.kuleuven.be/publications/talk-78.pdf
.. _ECRYPT: http://www.ecrypt.eu.org/documents/D.SPA.17.pdf
"""
__revision__ = "$Id$"
__all__ = ['generate', 'construct', 'error', 'DSAImplementation', '_DSAobj']
import sys
if sys.version_info[0] == 2 and sys.version_info[1] == 1:
from Crypto.Util.py21compat import *
from Crypto.PublicKey import _DSA, _slowmath, pubkey
from Crypto import Random
try:
from Crypto.PublicKey import _fastmath
except ImportError:
_fastmath = None
class _DSAobj(pubkey.pubkey):
"""Class defining an actual DSA key.
:undocumented: __getstate__, __setstate__, __repr__, __getattr__
"""
#: Dictionary of DSA parameters.
#:
#: A public key will only have the following entries:
#:
#: - **y**, the public key.
#: - **g**, the generator.
#: - **p**, the modulus.
#: - **q**, the order of the sub-group.
#:
#: A private key will also have:
#:
#: - **x**, the private key.
keydata = ['y', 'g', 'p', 'q', 'x']
def __init__(self, implementation, key):
self.implementation = implementation
self.key = key
def __getattr__(self, attrname):
if attrname in self.keydata:
# For backward compatibility, allow the user to get (not set) the
# DSA key parameters directly from this object.
return getattr(self.key, attrname)
else:
raise AttributeError("%s object has no %r attribute" % (self.__class__.__name__, attrname,))
def sign(self, M, K):
"""Sign a piece of data with DSA.
:Parameter M: The piece of data to sign with DSA. It may
not be longer in bit size than the sub-group order (*q*).
:Type M: byte string or long
:Parameter K: A secret number, chosen randomly in the closed
range *[1,q-1]*.
:Type K: long (recommended) or byte string (not recommended)
:attention: selection of *K* is crucial for security. Generating a
random number larger than *q* and taking the modulus by *q* is
**not** secure, since smaller values will occur more frequently.
Generating a random number systematically smaller than *q-1*
(e.g. *floor((q-1)/8)* random bytes) is also **not** secure. In general,
it shall not be possible for an attacker to know the value of `any
bit of K`__.
:attention: The number *K* shall not be reused for any other
operation and shall be discarded immediately.
:attention: M must be a digest cryptographic hash, otherwise
an attacker may mount an existential forgery attack.
:Return: A tuple with 2 longs.
.. __: http://www.di.ens.fr/~pnguyen/pub_NgSh00.htm
"""
return pubkey.pubkey.sign(self, M, K)
def verify(self, M, signature):
"""Verify the validity of a DSA signature.
:Parameter M: The expected message.
:Type M: byte string or long
:Parameter signature: The DSA signature to verify.
:Type signature: A tuple with 2 longs as return by `sign`
:Return: True if the signature is correct, False otherwise.
"""
return pubkey.pubkey.verify(self, M, signature)
def _encrypt(self, c, K):
raise TypeError("DSA cannot encrypt")
def _decrypt(self, c):
raise TypeError("DSA cannot decrypt")
def _blind(self, m, r):
raise TypeError("DSA cannot blind")
def _unblind(self, m, r):
raise TypeError("DSA cannot unblind")
def _sign(self, m, k):
return self.key._sign(m, k)
def _verify(self, m, sig):
(r, s) = sig
return self.key._verify(m, r, s)
def has_private(self):
return self.key.has_private()
def size(self):
return self.key.size()
def can_blind(self):
return False
def can_encrypt(self):
return False
def can_sign(self):
return True
def publickey(self):
return self.implementation.construct((self.key.y, self.key.g, self.key.p, self.key.q))
def __getstate__(self):
d = {}
for k in self.keydata:
try:
d[k] = getattr(self.key, k)
except AttributeError:
pass
return d
def __setstate__(self, d):
if not hasattr(self, 'implementation'):
self.implementation = DSAImplementation()
t = []
for k in self.keydata:
if not d.has_key(k):
break
t.append(d[k])
self.key = self.implementation._math.dsa_construct(*tuple(t))
def __repr__(self):
attrs = []
for k in self.keydata:
if k == 'p':
attrs.append("p(%d)" % (self.size()+1,))
elif hasattr(self.key, 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))
class DSAImplementation(object):
"""
A DSA key factory.
This class is only internally used to implement the methods of the
`Crypto.PublicKey.DSA` module.
"""
def __init__(self, **kwargs):
"""Create a new DSA key factory.
:Keywords:
use_fast_math : bool
Specify which mathematic library to use:
- *None* (default). Use fastest math available.
- *True* . Use fast math.
- *False* . Use slow math.
default_randfunc : callable
Specify how to collect random data:
- *None* (default). Use Random.new().read().
- not *None* . Use the specified function directly.
:Raise RuntimeError:
When **use_fast_math** =True but fast math is not available.
"""
use_fast_math = kwargs.get('use_fast_math', None)
if use_fast_math is None: # Automatic
if _fastmath is not None:
self._math = _fastmath
else:
self._math = _slowmath
elif use_fast_math: # Explicitly select fast math
if _fastmath is not None:
self._math = _fastmath
else:
raise RuntimeError("fast math module not available")
else: # Explicitly select slow math
self._math = _slowmath
self.error = self._math.error
# 'default_randfunc' parameter:
# None (default) - use Random.new().read
# not None - use the specified function
self._default_randfunc = kwargs.get('default_randfunc', None)
self._current_randfunc = None
def _get_randfunc(self, randfunc):
if randfunc is not None:
return randfunc
elif self._current_randfunc is None:
self._current_randfunc = Random.new().read
return self._current_randfunc
def generate(self, bits, randfunc=None, progress_func=None):
"""Randomly generate a fresh, new DSA key.
:Parameters:
bits : int
Key length, or size (in bits) of the DSA modulus
*p*.
It must be a multiple of 64, in the closed
interval [512,1024].
randfunc : callable
Random number generation function; it should accept
a single integer N and return a string of random data
N bytes long.
If not specified, a new one will be instantiated
from ``Crypto.Random``.
progress_func : callable
Optional function that will be called with a short string
containing the key parameter currently being generated;
it's useful for interactive applications where a user is
waiting for a key to be generated.
:attention: You should always use a cryptographically secure random number generator,
such as the one defined in the ``Crypto.Random`` module; **don't** just use the
current time and the ``random`` module.
:Return: A DSA key object (`_DSAobj`).
:Raise ValueError:
When **bits** is too little, too big, or not a multiple of 64.
"""
# Check against FIPS 186-2, which says that the size of the prime p
# must be a multiple of 64 bits between 512 and 1024
for i in (0, 1, 2, 3, 4, 5, 6, 7, 8):
if bits == 512 + 64*i:
return self._generate(bits, randfunc, progress_func)
# The March 2006 draft of FIPS 186-3 also allows 2048 and 3072-bit
# primes, but only with longer q values. Since the current DSA
# implementation only supports a 160-bit q, we don't support larger
# values.
raise ValueError("Number of bits in p must be a multiple of 64 between 512 and 1024, not %d bits" % (bits,))
def _generate(self, bits, randfunc=None, progress_func=None):
rf = self._get_randfunc(randfunc)
obj = _DSA.generate_py(bits, rf, progress_func) # TODO: Don't use legacy _DSA module
key = self._math.dsa_construct(obj.y, obj.g, obj.p, obj.q, obj.x)
return _DSAobj(self, key)
def construct(self, tup):
"""Construct a DSA key from a tuple of valid DSA components.
The modulus *p* must be a prime.
The following equations must apply:
- p-1 = 0 mod q
- g^x = y mod p
- 0 < x < q
- 1 < g < p
:Parameters:
tup : tuple
A tuple of long integers, with 4 or 5 items
in the following order:
1. Public key (*y*).
2. Sub-group generator (*g*).
3. Modulus, finite field order (*p*).
4. Sub-group order (*q*).
5. Private key (*x*). Optional.
:Return: A DSA key object (`_DSAobj`).
"""
key = self._math.dsa_construct(*tup)
return _DSAobj(self, key)
_impl = DSAImplementation()
generate = _impl.generate
construct = _impl.construct
error = _impl.error
# vim:set ts=4 sw=4 sts=4 expandtab: