# -*- 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 Crypto.Util.py3compat import bchr, bord, tobytes, tostr, iter_range

from Crypto import Random
from Crypto.IO import PKCS8, PEM
from Crypto.Hash import SHA256
from Crypto.Util.asn1 import (
                DerObject, DerSequence,
                DerInteger, DerObjectId,
                DerBitString,
                )

from Crypto.Math.Numbers import Integer
from Crypto.Math.Primality import (test_probable_prime, COMPOSITE,
                                   PROBABLY_PRIME)

from Crypto.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':
                attrs.append("p(%d)" % (self.size()+1,))
            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:`Crypto.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:`Crypto.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,
                                protection, key_params=params,
                                randfunc=randfunc
                                )
                if passphrase:
                    key_type = 'ENCRYPTED PRIVATE'
                else:
                    key_type = 'PRIVATE'
                passphrase = None
            else:
                if format != 'PEM' and passphrase:
                    raise ValueError("DSA private key cannot be encrypted")
                ints = [0, self.p, self.q, self.g, self.y, self.x]
                binary_key = DerSequence(ints).encode()
                key_type = "DSA PRIVATE"
        else:
            if pkcs8:
                raise ValueError("PKCS#8 is only meaningful for private keys")

            binary_key = _create_subject_public_key_info(oid,
                                DerInteger(self.y), params)
            key_type = "PUBLIC"

        if format == 'DER':
            return binary_key
        if format == 'PEM':
            pem_str = PEM.encode(
                                binary_key, key_type + " KEY",
                                passphrase, randfunc
                            )
            return tobytes(pem_str)
        raise ValueError("Unknown key format '%s'. Cannot export the DSA key." % format)

    # Backward-compatibility
    exportKey = export_key

    # Methods defined in PyCrypto that we don't support anymore

    def sign(self, M, K):
        raise NotImplementedError("Use module Crypto.Signature.DSS instead")

    def verify(self, M, signature):
        raise NotImplementedError("Use module Crypto.Signature.DSS instead")

    def encrypt(self, plaintext, K):
        raise NotImplementedError