pycryptodome/lib/Crypto/PublicKey/DSA.py

# -*- 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.
# ===================================================================

"""DSA public-key signature algorithm."""

__revision__ = "$Id$"

__all__ = ['generate', 'construct', 'error']

from Crypto.Util.python_compat 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):
    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 _encrypt(self, c, K):
        raise error("DSA cannot encrypt")

    def _decrypt(self, c):
        raise error("DSA cannot decrypt")

    def _blind(self, m, r):
        raise error("DSA cannot blind")

    def _unblind(self, m, r):
        raise error("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")
        return "<%s @0x%x %s>" % (self.__class__.__name__, id(self), ",".join(attrs))

class DSAImplementation(object):
    def __init__(self, **kwargs):
        # 'use_fast_math' parameter:
        #   None (default) - Use fast math if available; Use slow math if not.
        #   True - Use fast math, and raise RuntimeError if it's not available.
        #   False - Use slow math.
        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):
        # 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):
        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: