path: root/src/saml2/sigver.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# Copyright (C) 2009-2011 Umeå University
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#            http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

""" Functions connected to signing and verifying.
Based on the use of xmlsec1 binaries and not the python xmlsec module.
"""

import base64
from binascii import hexlify
import hashlib
import logging
import random
import os
from time import mktime
import urllib
import M2Crypto
from M2Crypto.X509 import load_cert_string
from saml2.samlp import Response

import xmldsig as ds

from saml2 import samlp
from saml2 import class_name
from saml2 import saml
from saml2 import ExtensionElement
from saml2 import VERSION

from saml2.s_utils import sid
from saml2.s_utils import Unsupported

from saml2.time_util import instant
from saml2.time_util import utc_now
from saml2.time_util import str_to_time

from tempfile import NamedTemporaryFile
from subprocess import Popen, PIPE

logger = logging.getLogger(__name__)

SIG = "{%s#}%s" % (ds.NAMESPACE, "Signature")

RSA_SHA1 = "http://www.w3.org/2000/09/xmldsig#rsa-sha1"


def signed(item):
    if SIG in item.c_children.keys() and item.signature:
        return True
    else:
        for prop in item.c_child_order:
            child = getattr(item, prop, None)
            if isinstance(child, list):
                for chi in child:
                    if signed(chi):
                        return True
            elif child and signed(child):
                return True

    return False


def _get_xmlsec_binary(paths=None):
    """
    Tries to find the xmlsec1 binary.

    :param paths: Non-system path paths which should be searched when
        looking for xmlsec1
    :return: full name of the xmlsec1 binary found. If no binaries are
        found then an exception is raised.
    """
    if os.name == "posix":
        bin_name = "xmlsec1"
    elif os.name == "nt":
        bin_name = "xmlsec1.exe"
    else:  # Default !?
        bin_name = "xmlsec1"

    if paths:
        for path in paths:
            fil = os.path.join(path, bin_name)
            try:
                if os.lstat(fil):
                    return fil
            except Exception:
                pass

    for path in os.environ["PATH"].split(os.pathsep):
        fil = os.path.join(path, bin_name)
        try:
            if os.lstat(fil):
                return fil
        except Exception:
            pass

    raise Exception("Can't find %s" % bin_name)

def _get_xmlsec_cryptobackend(path=None, search_paths=None, debug=False):
    """
    Initialize a CryptoBackendXmlSec1 crypto backend.

    This function is now internal to this module.
    """
    if path is None:
        path=_get_xmlsec_binary(paths=search_paths)
    return CryptoBackendXmlSec1(path, debug=debug)


ID_ATTR = "ID"
NODE_NAME = "urn:oasis:names:tc:SAML:2.0:assertion:Assertion"
ENC_NODE_NAME = "urn:oasis:names:tc:SAML:2.0:assertion:EncryptedAssertion"
ENC_KEY_CLASS = "EncryptedKey"

_TEST_ = True


class SignatureError(Exception):
    pass


class XmlsecError(Exception):
    pass


class MissingKey(Exception):
    pass


class DecryptError(Exception):
    pass

# --------------------------------------------------------------------------



def _make_vals(val, klass, seccont, klass_inst=None, prop=None, part=False,
               base64encode=False, elements_to_sign=None):
    """
    Creates a class instance with a specified value, the specified
    class instance may be a value on a property in a defined class instance.

    :param val: The value
    :param klass: The value class
    :param klass_inst: The class instance which has a property on which
        what this function returns is a value.
    :param prop: The property which the value should be assigned to.
    :param part: If the value is one of a possible list of values it should be
        handled slightly different compared to if it isn't.
    :return: Value class instance
    """
    cinst = None

    #print "make_vals(%s, %s)" % (val, klass)

    if isinstance(val, dict):
        cinst = _instance(klass, val, seccont, base64encode=base64encode,
                          elements_to_sign=elements_to_sign)
    else:
        try:
            cinst = klass().set_text(val)
        except ValueError:
            if not part:
                cis = [_make_vals(sval, klass, seccont, klass_inst, prop,
                       True, base64encode, elements_to_sign) for sval in val]
                setattr(klass_inst, prop, cis)
            else:
                raise

    if part:
        return cinst
    else:
        if cinst:
            cis = [cinst]
            setattr(klass_inst, prop, cis)


def _instance(klass, ava, seccont, base64encode=False, elements_to_sign=None):
    instance = klass()

    for prop in instance.c_attributes.values():
    #print "# %s" % (prop)
        if prop in ava:
            if isinstance(ava[prop], bool):
                setattr(instance, prop, "%s" % ava[prop])
            elif isinstance(ava[prop], int):
                setattr(instance, prop, "%d" % ava[prop])
            else:
                setattr(instance, prop, ava[prop])

    if "text" in ava:
        instance.set_text(ava["text"], base64encode)

    for prop, klassdef in instance.c_children.values():
        #print "## %s, %s" % (prop, klassdef)
        if prop in ava:
            #print "### %s" % ava[prop]
            if isinstance(klassdef, list):
                # means there can be a list of values
                _make_vals(ava[prop], klassdef[0], seccont, instance, prop,
                           base64encode=base64encode,
                           elements_to_sign=elements_to_sign)
            else:
                cis = _make_vals(ava[prop], klassdef, seccont, instance, prop,
                                 True, base64encode, elements_to_sign)
                setattr(instance, prop, cis)

    if "extension_elements" in ava:
        for item in ava["extension_elements"]:
            instance.extension_elements.append(
                ExtensionElement(item["tag"]).loadd(item))

    if "extension_attributes" in ava:
        for key, val in ava["extension_attributes"].items():
            instance.extension_attributes[key] = val

    if "signature" in ava:
        elements_to_sign.append((class_name(instance), instance.id))

    return instance


def signed_instance_factory(instance, seccont, elements_to_sign=None):
    """

    :param instance: The instance to be signed or not
    :param seccont: The security context
    :param elements_to_sign: Which parts if any that should be signed
    :return: A class instance if not signed otherwise a string
    """
    if elements_to_sign:
        signed_xml = "%s" % instance
        for (node_name, nodeid) in elements_to_sign:
            signed_xml = seccont.sign_statement(
                signed_xml, class_name=node_name, node_id=nodeid)

        #print "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
        #print "%s" % signed_xml
        #print "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
        return signed_xml
    else:
        return instance

# --------------------------------------------------------------------------


def create_id():
    """ Create a string of 40 random characters from the set [a-p],
    can be used as a unique identifier of objects.

    :return: The string of random characters
    """
    ret = ""
    for _ in range(40):
        ret += chr(random.randint(0, 15) + ord('a'))
    return ret


def make_temp(string, suffix="", decode=True):
    """ xmlsec needs files in some cases where only strings exist, hence the
    need for this function. It creates a temporary file with the
    string as only content.

    :param string: The information to be placed in the file
    :param suffix: The temporary file might have to have a specific
        suffix in certain circumstances.
    :param decode: The input string might be base64 coded. If so it
        must, in some cases, be decoded before being placed in the file.
    :return: 2-tuple with file pointer ( so the calling function can
        close the file) and filename (which is for instance needed by the
        xmlsec function).
    """
    ntf = NamedTemporaryFile(suffix=suffix)
    if decode:
        ntf.write(base64.b64decode(string))
    else:
        ntf.write(string)
    ntf.seek(0)
    return ntf, ntf.name


def split_len(seq, length):
    return [seq[i:i + length] for i in range(0, len(seq), length)]

# --------------------------------------------------------------------------

M2_TIME_FORMAT = "%b %d %H:%M:%S %Y"


def to_time(_time):
    assert _time.endswith(" GMT")
    _time = _time[:-4]
    return mktime(str_to_time(_time, M2_TIME_FORMAT))


def active_cert(key):
    cert_str = pem_format(key)
    certificate = load_cert_string(cert_str)
    not_before = to_time(str(certificate.get_not_before()))
    not_after = to_time(str(certificate.get_not_after()))
    try:
        assert not_before < utc_now()
        assert not_after > utc_now()
        return True
    except AssertionError:
        return False


def cert_from_key_info(key_info, ignore_age=False):
    """ Get all X509 certs from a KeyInfo instance. Care is taken to make sure
    that the certs are continues sequences of bytes.

    All certificates appearing in an X509Data element MUST relate to the
    validation key by either containing it or being part of a certification
    chain that terminates in a certificate containing the validation key.

    :param key_info: The KeyInfo instance
    :return: A possibly empty list of certs
    """
    res = []
    for x509_data in key_info.x509_data:
        #print "X509Data",x509_data
        x509_certificate = x509_data.x509_certificate
        cert = x509_certificate.text.strip()
        cert = "\n".join(split_len("".join([s.strip() for s in
                                            cert.split()]), 64))
        if ignore_age or active_cert(cert):
            res.append(cert)
        else:
            logger.info("Inactive cert")
    return res


def cert_from_key_info_dict(key_info, ignore_age=False):
    """ Get all X509 certs from a KeyInfo dictionary. Care is taken to make sure
    that the certs are continues sequences of bytes.

    All certificates appearing in an X509Data element MUST relate to the
    validation key by either containing it or being part of a certification
    chain that terminates in a certificate containing the validation key.

    :param key_info: The KeyInfo dictionary
    :return: A possibly empty list of certs in their text representation
    """
    res = []
    if not "x509_data" in key_info:
        return res

    for x509_data in key_info["x509_data"]:
        x509_certificate = x509_data["x509_certificate"]
        cert = x509_certificate["text"].strip()
        cert = "\n".join(split_len("".join([s.strip() for s in
                                            cert.split()]), 64))
        if ignore_age or active_cert(cert):
            res.append(cert)
        else:
            logger.info("Inactive cert")
    return res


def cert_from_instance(instance):
    """ Find certificates that are part of an instance

    :param instance: An instance
    :return: possible empty list of certificates
    """
    if instance.signature:
        if instance.signature.key_info:
            return cert_from_key_info(instance.signature.key_info,
                                      ignore_age=True)
    return []

# =============================================================================
from M2Crypto.__m2crypto import bn_to_mpi
from M2Crypto.__m2crypto import hex_to_bn


def intarr2long(arr):
    return long(''.join(["%02x" % byte for byte in arr]), 16)


def dehexlify(bi):
    s = hexlify(bi)
    return [int(s[i] + s[i + 1], 16) for i in range(0, len(s), 2)]


def long_to_mpi(num):
    """Converts a python integer or long to OpenSSL MPInt used by M2Crypto.
    Borrowed from Snowball.Shared.Crypto"""
    h = hex(num)[2:]  # strip leading 0x in string
    if len(h) % 2 == 1:
        h = '0' + h  # add leading 0 to get even number of hexdigits
    return bn_to_mpi(hex_to_bn(h))  # convert using OpenSSL BinNum


def base64_to_long(data):
    _d = base64.urlsafe_b64decode(data + '==')
    return intarr2long(dehexlify(_d))


def key_from_key_value(key_info):
    res = []
    for value in key_info.key_value:
        if value.rsa_key_value:
            e = base64_to_long(value.rsa_key_value.exponent)
            m = base64_to_long(value.rsa_key_value.modulus)
            key = M2Crypto.RSA.new_pub_key((long_to_mpi(e),
                                            long_to_mpi(m)))
            res.append(key)
    return res


def key_from_key_value_dict(key_info):
    res = []
    if not "key_value" in key_info:
        return res

    for value in key_info["key_value"]:
        if "rsa_key_value" in value:
            e = base64_to_long(value["rsa_key_value"]["exponent"])
            m = base64_to_long(value["rsa_key_value"]["modulus"])
            key = M2Crypto.RSA.new_pub_key((long_to_mpi(e),
                                            long_to_mpi(m)))
            res.append(key)
    return res

# =============================================================================


def rsa_load(filename):
    """Read a PEM-encoded RSA key pair from a file."""
    return M2Crypto.RSA.load_key(filename, M2Crypto.util.no_passphrase_callback)


def rsa_loads(key):
    """Read a PEM-encoded RSA key pair from a string."""
    return M2Crypto.RSA.load_key_string(key,
                                        M2Crypto.util.no_passphrase_callback)


def x509_rsa_loads(string):
    cert = M2Crypto.X509.load_cert_string(string)
    return cert.get_pubkey().get_rsa()


def pem_format(key):
    return "\n".join(["-----BEGIN CERTIFICATE-----",
                      key, "-----END CERTIFICATE-----"])


def parse_xmlsec_output(output):
    """ Parse the output from xmlsec to try to find out if the
    command was successfull or not.

    :param output: The output from Popen
    :return: A boolean; True if the command was a success otherwise False
    """
    for line in output.split("\n"):
        if line == "OK":
            return True
        elif line == "FAIL":
            raise XmlsecError(output)
    raise XmlsecError(output)


class BadSignature(Exception):
    """The signature is invalid."""
    pass


def sha1_digest(msg):
    return hashlib.sha1(msg).digest()


class Signer(object):
    """Abstract base class for signing algorithms."""
    def sign(self, msg, key):
        """Sign ``msg`` with ``key`` and return the signature."""
        raise NotImplementedError

    def verify(self, msg, sig, key):
        """Return True if ``sig`` is a valid signature for ``msg``."""
        raise NotImplementedError


class RSASigner(Signer):
    def __init__(self, digest, algo):
        self.digest = digest
        self.algo = algo

    def sign(self, msg, key):
        return key.sign(self.digest(msg), self.algo)

    def verify(self, msg, sig, key):
        try:
            return key.verify(self.digest(msg), sig, self.algo)
        except M2Crypto.RSA.RSAError, e:
            raise BadSignature(e)


REQ_ORDER = ["SAMLRequest", "RelayState", "SigAlg"]
RESP_ORDER = ["SAMLResponse", "RelayState", "SigAlg"]


def verify_redirect_signature(info, cert):
    """

    :param info: A dictionary as produced by parse_qs, means all values are
        lists.
    :param cert: A certificate to use when verifying the signature
    :return: True, if signature verified
    """

    if info["SigAlg"][0] == RSA_SHA1:
        if "SAMLRequest" in info:
            _order = REQ_ORDER
        elif "SAMLResponse" in info:
            _order = RESP_ORDER
        else:
            raise Unsupported(
                "Verifying signature on something that should not be signed")
        signer = RSASigner(sha1_digest, "sha1")
        args = info.copy()
        del args["Signature"]  # everything but the signature
        string = "&".join([urllib.urlencode({k: args[k][0]}) for k in _order])
        _key = x509_rsa_loads(pem_format(cert))
        _sign = base64.b64decode(info["Signature"][0])
        try:
            signer.verify(string, _sign, _key)
            return True
        except BadSignature:
            return False
    else:
        raise Unsupported("Signature algorithm: %s" % info["SigAlg"])

LOG_LINE = 60 * "=" + "\n%s\n" + 60 * "-" + "\n%s" + 60 * "="
LOG_LINE_2 = 60 * "=" + "\n%s\n%s\n" + 60 * "-" + "\n%s" + 60 * "="


# ---------------------------------------------------------------------------


def read_cert_from_file(cert_file, cert_type):
    """ Reads a certificate from a file. The assumption is that there is
    only one certificate in the file

    :param cert_file: The name of the file
    :param cert_type: The certificate type
    :return: A base64 encoded certificate as a string or the empty string
    """
    if not cert_file:
        return ""

    if cert_type == "pem":
        line = open(cert_file).read().split("\n")
        if line[0] == "-----BEGIN CERTIFICATE-----":
            line = line[1:]
        elif line[0] == "-----BEGIN PUBLIC KEY-----":
            line = line[1:]
        else:
            raise Exception("Strange beginning of PEM file")

        while line[-1] == "":
            line = line[:-1]

        if line[-1] == "-----END CERTIFICATE-----":
            line = line[:-1]
        elif line[-1] == "-----END PUBLIC KEY-----":
            line = line[:-1]
        else:
            raise Exception("Strange end of PEM file")
        return "".join(line)

    if cert_type in ["der", "cer", "crt"]:
        data = open(cert_file).read()
        return base64.b64encode(str(data))


class CryptoBackend():

    def __init__(self, debug=False):
        self.debug = debug

    def version(self):
        raise NotImplementedError()

    def encrypt(self, text, recv_key, template, key_type):
        raise NotImplementedError()

    def decrypt(self, enctext, key_file):
        raise NotImplementedError()

    def sign_statement(self, statement, class_name, key_file, nodeid,
                       id_attr):
        raise NotImplementedError()

    def validate_signature(self, enctext, cert_file, cert_type, node_name,
                           node_id, id_attr):
        raise NotImplementedError()


class CryptoBackendXmlSec1(CryptoBackend):
    """
    CryptoBackend implementation using external binary xmlsec1 to sign
    and verify XML documents.
    """

    __DEBUG = 0

    def __init__(self, xmlsec_binary, **kwargs):
        CryptoBackend.__init__(self, **kwargs)
        assert(isinstance(xmlsec_binary, basestring))
        self.xmlsec = xmlsec_binary

    def version(self):
        com_list = [self.xmlsec, "--version"]
        pof = Popen(com_list, stderr=PIPE, stdout=PIPE)
        try:
            return pof.stdout.read().split(" ")[1]
        except Exception:
            return ""

    def encrypt(self, text, recv_key, template, key_type):
        logger.info("Encryption input len: %d" % len(text))
        _, fil = make_temp("%s" % text, decode=False)

        com_list = [self.xmlsec, "--encrypt", "--pubkey-cert-pem", recv_key,
                    "--session-key", key_type, "--xml-data", fil,
                    ]

        (_stdout, _stderr, output) = self._run_xmlsec(com_list, [template],
                                                      exception=DecryptError,
                                                      validate_output=False)
        return output

    def decrypt(self, enctext, key_file):
        logger.info("Decrypt input len: %d" % len(enctext))
        _, fil = make_temp("%s" % enctext, decode=False)

        com_list = [self.xmlsec, "--decrypt", "--privkey-pem",
                    key_file, "--id-attr:%s" % ID_ATTR, ENC_KEY_CLASS,
                    ]

        (_stdout, _stderr, output) = self._run_xmlsec(com_list, [fil],
                                                      exception=DecryptError,
                                                      validate_output=False)
        return output

    def sign_statement(self, statement, class_name, key_file, node_id,
                       id_attr):
        """
        Sign an XML statement.

        :param statement: The statement to be signed
        :param class_name: string like 'urn:oasis:names:...:Assertion'
        :param key_file: The file where the key can be found
        :param node_id:
        :param id_attr: The attribute name for the identifier, normally one of
            'id','Id' or 'ID'
        :return: The signed statement
        """

        _, fil = make_temp("%s" % statement, decode=False)

        com_list = [self.xmlsec, "--sign",
                    "--privkey-pem", key_file,
                    "--id-attr:%s" % id_attr, class_name,
                    #"--store-signatures"
                    ]
        if node_id:
            com_list.extend(["--node-id", node_id])

        try:
            (stdout, stderr, signed_statement) = \
                self._run_xmlsec(com_list, [fil], validate_output=False)
            # this doesn't work if --store-signatures are used
            if stdout == "":
                if signed_statement:
                    return signed_statement
            logger.error(
                "Signing operation failed :\nstdout : %s\nstderr : %s" % (
                    stdout, stderr))
            raise Exception("Signing failed")
        except DecryptError:
            raise Exception("Signing failed")

    def validate_signature(self, signedtext, cert_file, cert_type, node_name,
                           node_id, id_attr):
        """
        Validate signature on XML document.

        :param signedtext: The XML document as a string
        :param cert_file: The public key that was used to sign the document
        :param cert_type: The file type of the certificate
        :param node_name: The name of the class that is signed
        :param node_id: The identifier of the node
        :param id_attr: Should normally be one of "id", "Id" or "ID"
        :return: Boolean True if the signature was correct otherwise False.
        """
        _, fil = make_temp(signedtext, decode=False)

        com_list = [self.xmlsec, "--verify",
                    "--pubkey-cert-%s" % cert_type, cert_file,
                    "--id-attr:%s" % id_attr, node_name]

        if self.debug:
            com_list.append("--store-signatures")

        if node_id:
            com_list.extend(["--node-id", node_id])

        if self.__DEBUG:
            try:
                print " ".join(com_list)
            except TypeError:
                print "cert_type", cert_type
                print "cert_file", cert_file
                print "node_name", node_name
                print "fil", fil
                raise
            print "%s: %s" % (cert_file, os.access(cert_file, os.F_OK))
            print "%s: %s" % (fil, os.access(fil, os.F_OK))

        (_stdout, stderr, _output) = self._run_xmlsec(com_list, [fil],
                                                      exception=SignatureError)
        return parse_xmlsec_output(stderr)

    def _run_xmlsec(self, com_list, extra_args, validate_output=True,
                    exception=XmlsecError):
        """
        Common code to invoke xmlsec and parse the output.
        :param com_list: Key-value parameter list for xmlsec
        :param extra_args: Positional parameters to be appended after all
            key-value parameters
        :param validate_output: Parse and validate the output
        :param exception: The exception class to raise on errors
        :result: Whatever xmlsec wrote to an --output temporary file
        """
        ntf = NamedTemporaryFile()
        com_list.extend(["--output", ntf.name])
        com_list += extra_args

        logger.debug("xmlsec command: %s" % " ".join(com_list))

        pof = Popen(com_list, stderr=PIPE, stdout=PIPE)

        p_out = pof.stdout.read()
        p_err = pof.stderr.read()
        try:
            if validate_output:
                parse_xmlsec_output(p_err)
        except XmlsecError, exc:
            logger.error(LOG_LINE_2 % (p_out, p_err, exc))
            raise exception("%s" % (exc,))

        ntf.seek(0)
        return p_out, p_err, ntf.read()

class CryptoBackendXMLSecurity(CryptoBackend):
    """
    CryptoBackend implementation using pyXMLSecurity to sign and verify
    XML documents.

    Encrypt and decrypt is currently unsupported by pyXMLSecurity.

    pyXMLSecurity uses lxml (libxml2) to parse XML data, but otherwise
    try to get by with native Python code. It does native Python RSA
    signatures, or alternatively PyKCS11 to offload cryptographic work
    to an external PKCS#11 module.
    """

    def __init__(self, debug=False):
        CryptoBackend.__init__(self)
        self.debug = debug

    def version():
        # XXX if XMLSecurity.__init__ included a __version__, that would be
        # better than static 0.0 here.
        return "XMLSecurity 0.0"

    def sign_statement(self, statement, _class_name, key_file, _nodeid,
                       _id_attr):
        """
        Sign an XML statement.

        The parameters actually used in this CryptoBackend
        implementation are :

        :param statement: XML as string
        :param key_file: xmlsec key_spec string(), filename,
            "pkcs11://" URI or PEM data
        :returns: Signed XML as string
        """
        import xmlsec
        import lxml.etree
        xml = xmlsec.parse_xml(statement)
        signed = xmlsec.sign(xml, key_file)
        return lxml.etree.tostring(signed, xml_declaration=True)

    def validate_signature(self, signedtext, cert_file, cert_type, _node_name,
                           _node_id, _id_attr):
        """
        Validate signature on XML document.

        The parameters actually used in this CryptoBackend
        implementation are :

        :param signedtext: The signed XML data as string
        :param cert_file: xmlsec key_spec string(), filename,
            "pkcs11://" URI or PEM data
        :param cert_type: string, must be 'pem' for now
        :returns: True on successful validation, False otherwise
        """
        if cert_type != "pem":
            raise Unsupported("Only PEM certs supported here")
        import xmlsec
        xml = xmlsec.parse_xml(signedtext)
        try:
            return xmlsec.verify(xml, cert_file)
        except xmlsec.XMLSigException:
            return False

def security_context(conf, debug=None):
    """ Creates a security context based on the configuration

    :param conf: The configuration
    :return: A SecurityContext instance
    """
    if not conf:
        return None

    if debug is None:
        debug = conf.debug

    metadata = conf.metadata

    _only_md = conf.only_use_keys_in_metadata
    if _only_md is None:
        _only_md = False

    if conf.crypto_backend == 'xmlsec1':
        xmlsec_binary = conf.xmlsec_binary
        if not xmlsec_binary:
            xmlsec_binary = _get_xmlsec_binary()
        # verify that xmlsec is where it's supposed to be
        if not os.path.exists(xmlsec_binary):
            #if not os.access(, os.F_OK):
            raise Exception(
                "xmlsec binary not in '%s' !" % xmlsec_binary)
        crypto = _get_xmlsec_cryptobackend(xmlsec_binary, debug=debug)
    elif conf.crypto_backend == 'XMLSecurity':
        # new and somewhat untested pyXMLSecurity crypto backend.
        crypto = CryptoBackendXMLSecurity(debug=debug)
    else:
        raise Exception('Unknown crypto_backend %s' % (
                repr(conf.crypto_backend)))

    return SecurityContext(crypto, conf.key_file,
                           cert_file=conf.cert_file, metadata=metadata,
                           debug=debug, only_use_keys_in_metadata=_only_md)


class SecurityContext(object):
    def __init__(self, crypto, key_file="", key_type="pem",
                 cert_file="", cert_type="pem", metadata=None,
                 debug=False, template="", encrypt_key_type="des-192",
                 only_use_keys_in_metadata=False):

        self.crypto = crypto
        assert (isinstance(self.crypto, CryptoBackend))

        # Your private key
        self.key_file = key_file
        self.key_type = key_type

        # Your public key
        self.cert_file = cert_file
        self.cert_type = cert_type
        self.my_cert = read_cert_from_file(cert_file, cert_type)

        self.metadata = metadata
        self.only_use_keys_in_metadata = only_use_keys_in_metadata
        self.debug = debug

        if not template:
            this_dir, this_filename = os.path.split(__file__)
            self.template = os.path.join(this_dir, "xml", "template.xml")
        else:
            self.template = template

        self.encrypt_key_type = encrypt_key_type

    def correctly_signed(self, xml, must=False):
        logger.info("verify correct signature")
        return self.correctly_signed_response(xml, must)

    def encrypt(self, text, recv_key="", template="", key_type=""):
        """
        xmlsec encrypt --pubkey-pem pub-userkey.pem
            --session-key aes128-cbc --xml-data doc-plain.xml
            --output doc-encrypted.xml session-key-template.xml

        :param text: Text to encrypt
        :param recv_key: A file containing the receivers public key
        :param template: A file containing the XML document template
        :param key_type: The type of session key to use
        :result: An encrypted XML text
        """
        if not key_type:
            key_type = self.encrypt_key_type
        if not template:
            template = self.template

        return self.crypto.encrypt(text, recv_key, template, key_type)

    def decrypt(self, enctext):
        """ Decrypting an encrypted text by the use of a private key.

        :param enctext: The encrypted text as a string
        :return: The decrypted text
        """
        return self.crypto.decrypt(enctext, self.key_file)

    def verify_signature(self, signedtext, cert_file=None, cert_type="pem",
                         node_name=NODE_NAME, node_id=None, id_attr=""):
        """ Verifies the signature of a XML document.

        :param signedtext: The XML document as a string
        :param cert_file: The public key that was used to sign the document
        :param cert_type: The file type of the certificate
        :param node_name: The name of the class that is signed
        :param node_id: The identifier of the node
        :param id_attr: Should normally be one of "id", "Id" or "ID"
        :return: Boolean True if the signature was correct otherwise False.
        """
        # This is only for testing purposes, otherwise when would you receive
        # stuff that is signed with your key !?
        if not cert_file:
            cert_file = self.cert_file
            cert_type = self.cert_type

        if not id_attr:
            id_attr = ID_ATTR

        return self.crypto.validate_signature(signedtext, cert_file=cert_file,
                                              cert_type=cert_type,
                                              node_name=node_name,
                                              node_id=node_id, id_attr=id_attr,
                                              )

    def _check_signature(self, decoded_xml, item, node_name=NODE_NAME,
                         origdoc=None, id_attr="", must=False):
        #print item
        try:
            issuer = item.issuer.text.strip()
        except AttributeError:
            issuer = None

        # More trust in certs from metadata then certs in the XML document
        if self.metadata:
            try:
                _certs = self.metadata.certs(issuer, "any", "signing")
            except KeyError:
                _certs = []
            certs = []
            for cert in _certs:
                if isinstance(cert, basestring):
                    certs.append(make_temp(pem_format(cert), ".pem", False))
                else:
                    certs.append(cert)
        else:
            certs = []

        if not certs and not self.only_use_keys_in_metadata:
            logger.debug("==== Certs from instance ====")
            certs = [make_temp(pem_format(cert), ".pem",
                               False) for cert in cert_from_instance(item)]
        else:
            logger.debug("==== Certs from metadata ==== %s: %s ====" % (issuer,
                                                                        certs))

        if not certs:
            raise MissingKey("%s" % issuer)

        #print certs

        verified = False
        for _, pem_file in certs:
            try:
                if origdoc is not None:
                    if self.verify_signature(origdoc, pem_file,
                                             node_name=node_name,
                                             node_id=item.id, id_attr=id_attr):
                        verified = True
                        break
                else:
                    if self.verify_signature(decoded_xml, pem_file,
                                             node_name=node_name,
                                             node_id=item.id, id_attr=id_attr):
                        verified = True
                        break
            except XmlsecError, exc:
                logger.error("check_sig: %s" % exc)
                pass
            except Exception, exc:
                logger.error("check_sig: %s" % exc)
                raise

        if not verified:
            raise SignatureError("Failed to verify signature")

        return item

    def check_signature(self, item, node_name=NODE_NAME, origdoc=None,
                        id_attr="", must=False):
        return self._check_signature(origdoc, item, node_name, origdoc,
                                     id_attr=id_attr, must=must)

    def correctly_signed_message(self, decoded_xml, msgtype, must=False,
                                 origdoc=None):
        """Check if a request is correctly signed, if we have metadata for
        the entity that sent the info use that, if not use the key that are in
        the message if any.

        :param decoded_xml: The SAML message as a XML string
        :param msgtype:
        :param must: Whether there must be a signature
        :param origdoc:
        :return:
        """

        try:
            _func = getattr(samlp, "%s_from_string" % msgtype)
        except AttributeError:
            _func = getattr(saml, "%s_from_string" % msgtype)

        msg = _func(decoded_xml)
        if not msg:
            raise TypeError("Not a %s" % msgtype)

        if not msg.signature:
            if must:
                raise SignatureError("Missing must signature")
            else:
                return msg

        return self._check_signature(decoded_xml, msg, class_name(msg),
                                     origdoc, must=must)

    def correctly_signed_authn_request(self, decoded_xml, must=False,
                                       origdoc=None):
        return self.correctly_signed_message(decoded_xml, "authn_request",
                                             must, origdoc)

    def correctly_signed_authn_query(self, decoded_xml, must=False,
                                     origdoc=None):
        return self.correctly_signed_message(decoded_xml, "authn_query",
                                             must, origdoc)

    def correctly_signed_logout_request(self, decoded_xml, must=False,
                                        origdoc=None):
        return self.correctly_signed_message(decoded_xml, "logout_request",
                                             must, origdoc)

    def correctly_signed_logout_response(self, decoded_xml, must=False,
                                         origdoc=None):
        return self.correctly_signed_message(decoded_xml, "logout_response",
                                             must, origdoc)

    def correctly_signed_attribute_query(self, decoded_xml, must=False,
                                         origdoc=None):
        return self.correctly_signed_message(decoded_xml, "attribute_query",
                                             must, origdoc)

    def correctly_signed_authz_decision_query(self, decoded_xml, must=False,
                                              origdoc=None):
        return self.correctly_signed_message(decoded_xml,
                                             "authz_decision_query", must,
                                             origdoc)

    def correctly_signed_authz_decision_response(self, decoded_xml, must=False,
                                                 origdoc=None):
        return self.correctly_signed_message(decoded_xml,
                                             "authz_decision_response", must,
                                             origdoc)

    def correctly_signed_name_id_mapping_request(self, decoded_xml, must=False,
                                                 origdoc=None):
        return self.correctly_signed_message(decoded_xml,
                                             "name_id_mapping_request",
                                             must, origdoc)

    def correctly_signed_name_id_mapping_response(self, decoded_xml, must=False,
                                                  origdoc=None):
        return self.correctly_signed_message(decoded_xml,
                                             "name_id_mapping_response",
                                             must, origdoc)

    def correctly_signed_artifact_request(self, decoded_xml, must=False,
                                          origdoc=None):
        return self.correctly_signed_message(decoded_xml,
                                             "artifact_request",
                                             must, origdoc)

    def correctly_signed_artifact_response(self, decoded_xml, must=False,
                                           origdoc=None):
        return self.correctly_signed_message(decoded_xml,
                                             "artifact_response",
                                             must, origdoc)

    def correctly_signed_manage_name_id_request(self, decoded_xml, must=False,
                                                origdoc=None):
        return self.correctly_signed_message(decoded_xml,
                                             "manage_name_id_request",
                                             must, origdoc)

    def correctly_signed_manage_name_id_response(self, decoded_xml, must=False,
                                                 origdoc=None):
        return self.correctly_signed_message(decoded_xml,
                                             "manage_name_id_response", must,
                                             origdoc)

    def correctly_signed_assertion_id_request(self, decoded_xml, must=False,
                                              origdoc=None):
        return self.correctly_signed_message(decoded_xml,
                                             "assertion_id_request", must,
                                             origdoc)

    def correctly_signed_assertion_id_response(self, decoded_xml, must=False,
                                               origdoc=None):
        return self.correctly_signed_message(decoded_xml, "assertion", must,
                                             origdoc)

    def correctly_signed_response(self, decoded_xml, must=False, origdoc=None):
        """ Check if a instance is correctly signed, if we have metadata for
        the IdP that sent the info use that, if not use the key that are in
        the message if any.

        :param decoded_xml: The SAML message as a XML string
        :param must: Whether there must be a signature
        :param origdoc:
        :return: None if the signature can not be verified otherwise an instance
        """

        response = samlp.any_response_from_string(decoded_xml)
        if not response:
            raise TypeError("Not a Response")

        if response.signature:
            self._check_signature(decoded_xml, response, class_name(response),
                                  origdoc)

        if isinstance(response, Response) and response.assertion:
            # Try to find the signing cert in the assertion
            for assertion in response.assertion:
                if not assertion.signature:
                    logger.debug("unsigned")
                    if must:
                        raise SignatureError("Signature missing")
                    continue
                else:
                    logger.debug("signed")

                try:
                    self._check_signature(decoded_xml, assertion,
                                          class_name(assertion), origdoc)
                except Exception, exc:
                    logger.error("correctly_signed_response: %s" % exc)
                    raise

        return response

    #--------------------------------------------------------------------------
    # SIGNATURE PART
    #--------------------------------------------------------------------------
    def sign_statement_using_xmlsec(self, statement, **kwargs):
        """ Deprecated function. See sign_statement(). """
        return self.sign_statement(statement, **kwargs)

    def sign_statement(self, statement, class_name, key=None,
                       key_file=None, node_id=None, id_attr=""):
        """Sign a SAML statement.

        :param statement: The statement to be signed
        :param class_name: string like 'urn:oasis:names:...:Assertion'
        :param key: The key to be used for the signing, either this or
        :param key_file: The file where the key can be found
        :param node_id:
        :param id_attr: The attribute name for the identifier, normally one of
            'id','Id' or 'ID'
        :return: The signed statement
        """
        if not id_attr:
            id_attr = ID_ATTR

        if not key_file and key:
            _, key_file = make_temp("%s" % key, ".pem")

        if not key and not key_file:
            key_file = self.key_file

        return self.crypto.sign_statement(statement, class_name, key_file,
                                          node_id, id_attr)

    def sign_assertion_using_xmlsec(self, statement, **kwargs):
        """ Deprecated function. See sign_assertion(). """
        return self.sign_statement(statement, class_name(saml.Assertion()),
                                   **kwargs)

    def sign_assertion(self, statement, **kwargs):
        """Sign a SAML assertion.

        See sign_statement() for the kwargs.

        :param statement: The statement to be signed
        :return: The signed statement
        """
        return self.sign_statement(statement, class_name(saml.Assertion()),
                                   **kwargs)

    def sign_attribute_query_using_xmlsec(self, statement, **kwargs):
        """ Deprecated function. See sign_attribute_query(). """
        return self.sign_attribute_query(statement, **kwargs)

    def sign_attribute_query(self, statement, **kwargs):
        """Sign a SAML attribute query.

        See sign_statement() for the kwargs.

        :param statement: The statement to be signed
        :return: The signed statement
        """
        return self.sign_statement(statement, class_name(
            samlp.AttributeQuery()), **kwargs)

    def multiple_signatures(self, statement, to_sign, key=None, key_file=None):
        """
        Sign multiple parts of a statement

        :param statement: The statement that should be sign, this is XML text
        :param to_sign: A list of (items, id, id attribute name) tuples that
            specifies what to sign
        :param key: A key that should be used for doing the signing
        :param key_file: A file that contains the key to be used
        :return: A possibly multiple signed statement
        """
        for (item, sid, id_attr) in to_sign:
            if not sid:
                if not item.id:
                    sid = item.id = sid()
                else:
                    sid = item.id

            if not item.signature:
                item.signature = pre_signature_part(sid, self.cert_file)

            statement = self.sign_statement(statement, class_name(item),
                                            key=key, key_file=key_file,
                                            node_id=sid, id_attr=id_attr)
        return statement


# ===========================================================================


def pre_signature_part(ident, public_key=None, identifier=None):
    """
    If an assertion is to be signed the signature part has to be preset
    with which algorithms to be used, this function returns such a
    preset part.

    :param ident: The identifier of the assertion, so you know which assertion
        was signed
    :param public_key: The base64 part of a PEM file
    :param identifier:
    :return: A preset signature part
    """

    signature_method = ds.SignatureMethod(algorithm=ds.SIG_RSA_SHA1)
    canonicalization_method = ds.CanonicalizationMethod(
        algorithm=ds.ALG_EXC_C14N)
    trans0 = ds.Transform(algorithm=ds.TRANSFORM_ENVELOPED)
    trans1 = ds.Transform(algorithm=ds.ALG_EXC_C14N)
    transforms = ds.Transforms(transform=[trans0, trans1])
    digest_method = ds.DigestMethod(algorithm=ds.DIGEST_SHA1)

    reference = ds.Reference(uri="#%s" % ident, digest_value=ds.DigestValue(),
                             transforms=transforms, digest_method=digest_method)

    signed_info = ds.SignedInfo(signature_method=signature_method,
                                canonicalization_method=canonicalization_method,
                                reference=reference)

    signature = ds.Signature(signed_info=signed_info,
                             signature_value=ds.SignatureValue())

    if identifier:
        signature.id = "Signature%d" % identifier

    if public_key:
        x509_data = ds.X509Data(
            x509_certificate=[ds.X509Certificate(text=public_key)])
        key_info = ds.KeyInfo(x509_data=x509_data)
        signature.key_info = key_info

    return signature


def response_factory(sign=False, encrypt=False, **kwargs):
    response = samlp.Response(id=sid(), version=VERSION,
                              issue_instant=instant())

    if sign:
        response.signature = pre_signature_part(kwargs["id"])
    if encrypt:
        pass

    for key, val in kwargs.items():
        setattr(response, key, val)

    return response