trc.py

# Copyright 2014 ETH Zurich
#
# 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.
"""
:mod:`trc` --- SCION TRC parser
===============================================
"""
# Stdlib
import base64
import copy
import json
import logging
import time

# External
import lz4

# SCION
from lib.crypto.asymcrypto import verify, sign
from lib.packet.scion_addr import ISD_AS

ISDID_STRING = 'ISDID'
DESCRIPTION_STRING = 'Description'
VERSION_STRING = 'Version'
CREATION_TIME_STRING = 'CreationTime'
EXPIRATION_TIME_STRING = 'ExpirationTime'
CORE_ASES_STRING = 'CoreCAs'
ROOT_CAS_STRING = 'RootCAs'
PKI_LOGS_STRING = 'PKILogs'
QUORUM_EEPKI_STRING = 'QuorumEEPKI'
RAINS_STRING = 'RAINS'
ROOT_RAINS_KEY_STRING = 'RootRainsKey'
QUORUM_OWN_TRC_STRING = 'QuorumOwnTRC'
QUORUM_CAS_STRING = 'QuorumCAs'
QUARANTINE_STRING = 'Quarantine'
SIGNATURES_STRING = 'Signatures'
GRACE_PERIOD_STRING = 'GracePeriod'
ONLINE_KEY_ALG_STRING = 'OnlineKeyAlg'
ONLINE_KEY_STRING = 'OnlineKey'
OFFLINE_KEY_ALG_STRING = 'OfflineKeyAlg'
OFFLINE_KEY_STRING = 'OfflineKey'
CERTIFICATE_STRING = 'Certificate'


class TRC(object):
    """
    The TRC class parses the TRC file of an ISD and stores such
    information for further use.

    :ivar int isd: the ISD identifier.
    :ivar str description: is a human readable description of an ISD.
    :ivar int version: the TRC file version.
    :ivar int creation_time: the TRC file creation timestamp.
    :ivar int expiration_time: the time when TRC expires.
    :ivar dict core_ases: the set of core ASes and their certificates.
    :ivar dict root_cas: the set of root CAs and their certificates.
    :ivar dict pki_logs: is a dictionary of end entity certificate logs, and
        their addresses and public key certificates
    :ivar int quroum_eepki: is a threshold number (nonnegative integer) of
        CAs that have to sign a domain’s policy
    :ivar str root_rains_key: the RAINS root public key.
    :ivar int quorum_own_trc: number of core ASes necessary to sign a new TRC.
    :ivar int quorum_cas: number of CAs necessary to change CA entries
    :ivar int grace_period: defines for how long this TRC is valid when a new
        TRC is available
    :ivar bool quarantine: flag defining whether TRC is valid(quarantine=false)
        or an early annoncement(quarantine=true)
    :ivar dict signatures: signatures generated by a quorum of trust roots.
    """

    FIELDS_MAP = {
        ISDID_STRING: ("isd", int),
        DESCRIPTION_STRING: ("description", str),
        VERSION_STRING: ("version", int),
        CREATION_TIME_STRING: ("time", int),
        EXPIRATION_TIME_STRING: ("exp_time", int),
        CORE_ASES_STRING: ("core_ases", dict),
        ROOT_CAS_STRING: ("root_cas", dict),
        PKI_LOGS_STRING: ("pki_logs", dict),
        QUORUM_EEPKI_STRING: ("quorum_eepki", int),
        RAINS_STRING: ("rains", dict),
        QUORUM_OWN_TRC_STRING: ("quorum_own_trc", int),
        QUORUM_CAS_STRING: ("quorum_cas", int),
        QUARANTINE_STRING: ("quarantine", bool),
        SIGNATURES_STRING: ("signatures", dict),
        GRACE_PERIOD_STRING: ("grace_period", int),
    }
    DEFAULT_VALIDITY = 365 * 24 * 60 * 60

    def __init__(self, trc_dict):
        """
        :param dict trc_dict: TRC as dict.
        """
        for k, (name, type_) in self.FIELDS_MAP.items():
            val = trc_dict[k]
            if type_ in (int,):
                val = int(val)
            elif type_ in (dict, ):
                val = copy.deepcopy(val)
            elif type_ in (bytes, ):
                val = base64.b64decode(val.encode('utf-8'))
            setattr(self, name, val)
        for subject in trc_dict[CORE_ASES_STRING]:
            key = trc_dict[CORE_ASES_STRING][subject][ONLINE_KEY_STRING]
            self.core_ases[subject][ONLINE_KEY_STRING] = base64.b64decode(key.encode('utf-8'))
            key = trc_dict[CORE_ASES_STRING][subject][OFFLINE_KEY_STRING]
            self.core_ases[subject][OFFLINE_KEY_STRING] = base64.b64decode(key.encode('utf-8'))
        for subject in trc_dict[SIGNATURES_STRING]:
            sig = trc_dict[SIGNATURES_STRING][subject]
            self.signatures[subject] = base64.b64decode(sig.encode('utf-8'))
        for subject in trc_dict[ROOT_CAS_STRING]:
            key = trc_dict[ROOT_CAS_STRING][subject][CERTIFICATE_STRING]
            self.root_cas[subject][CERTIFICATE_STRING] = base64.b64decode(key.encode('utf-8'))
            key = trc_dict[ROOT_CAS_STRING][subject][ONLINE_KEY_STRING]
            self.root_cas[subject][ONLINE_KEY_STRING] = base64.b64decode(key.encode('utf-8'))
        if trc_dict[RAINS_STRING]:
            key = trc_dict[RAINS_STRING][ROOT_RAINS_KEY_STRING]
            self.rains[ROOT_RAINS_KEY_STRING] = base64.b64decode(key.encode('utf-8'))
            key = trc_dict[RAINS_STRING][ONLINE_KEY_STRING]
            self.rains[ONLINE_KEY_STRING] = base64.b64decode(key.encode('utf-8'))

    def get_isd_ver(self):
        return self.isd, self.version

    def get_core_ases(self):
        res = []
        for key in self.core_ases:
            res.append(ISD_AS(key))
        return res

    def dict(self, with_signatures):
        """
        Return the TRC information.

        :param bool with_signatures:
            If True, include signatures in the return value.
        :returns: the TRC information.
        :rtype: dict
        """
        trc_dict = {}
        for k, (name, _) in self.FIELDS_MAP.items():
            trc_dict[k] = getattr(self, name)
        if not with_signatures:
            del trc_dict[SIGNATURES_STRING]
        return trc_dict

    @classmethod
    def from_raw(cls, trc_raw, lz4_=False):
        if lz4_:
            trc_raw = lz4.loads(trc_raw).decode("utf-8")
        trc = json.loads(trc_raw)
        return TRC(trc)

    @classmethod
    def from_values(cls, isd, description, version, core_ases, root_cas,
                    pki_logs, quorum_eepki, rains, quorum_own_trc,
                    quorum_cas, grace_period, quarantine, signatures):
        """
        Generate a TRC instance.
        """
        now = int(time.time())
        trc_dict = {
            ISDID_STRING: isd,
            DESCRIPTION_STRING: description,
            VERSION_STRING: version,
            CREATION_TIME_STRING: now,
            EXPIRATION_TIME_STRING: now + cls.DEFAULT_VALIDITY,
            CORE_ASES_STRING: core_ases,
            ROOT_CAS_STRING: root_cas,
            PKI_LOGS_STRING: pki_logs,
            QUORUM_EEPKI_STRING: quorum_eepki,
            RAINS_STRING: rains,
            QUORUM_OWN_TRC_STRING: quorum_own_trc,
            QUORUM_CAS_STRING: quorum_cas,
            GRACE_PERIOD_STRING: grace_period,
            QUARANTINE_STRING: quarantine,
            SIGNATURES_STRING: signatures,
        }
        trc = TRC(trc_dict)
        return trc

    def sign(self, isd_as, sig_priv_key):
        data = self._sig_input()
        self.signatures[isd_as] = sign(data, sig_priv_key)

    def verify(self, old_trc):
        """
        Perform signature verification for core signatures as defined
        in old TRC.

        :param: old_trc: the previous TRC which has already been verified.
        :returns: True if verification succeeds, false otherwise.
        :rtype: bool
        """
        # Only look at signatures which are from core ASes as defined in old TRC
        signatures = {k: self.signatures[k] for k in old_trc.core_ases.keys()}
        # We have more signatures than the number of core ASes in old TRC
        if len(signatures) < len(self.signatures):
            logging.warning("TRC has more signatures than number of core ASes.")
        valid_signature_signers = set()
        # Add every signer to this set whose signature was verified successfully
        for signer in signatures:
            public_key = self.core_ases[signer].subject_sig_key_raw
            if self.verify_signature(signatures[signer], public_key):
                valid_signature_signers.add(signer)
            else:
                logging.warning("TRC contains a signature which could not be verified.")
        # We have fewer valid signatrues for this TRC than quorum_own_trc
        if len(valid_signature_signers) < old_trc.quorum_own_trc:
            logging.error("TRC does not have the number of required valid signatures")
            return False
        logging.debug("TRC verified.")
        return True

    def verify_signature(self, signature, public_key):
        """
        Checks if the signature can be verified with the given public key for a
        single signature

        :returns: True if the given signature could be verified with the
            given key, False otherwise
        :rtype bool
        """
        if not verify(self._sig_input(), signature, public_key):
            return False
        return True

    def _sig_input(self):
        d = self.dict(False)
        for k in d:
            if self.FIELDS_MAP[k][1] == str:
                d[k] = base64.b64encode(d[k].encode('utf-8')).decode('utf-8')
            elif self.FIELDS_MAP[k][1] == dict:
                d[k] = self._encode_dict(d[k])
            elif self.FIELDS_MAP[k][1] == bytes:
                d[k] = base64.b64encode(d[k]).decode('utf-8')
        j = json.dumps(d, sort_keys=True, separators=(',', ':'))
        return j.encode('utf-8')

    def _encode_dict(self, dict_):
        encoded_dict = {}
        for key_ in dict_:
            if type(dict_[key_]) is str:
                encoded_dict[key_] = base64.b64encode(dict_[key_].encode('utf-8')).decode('utf-8')
        return encoded_dict

    def to_json(self, with_signatures=True):
        """
        Convert the instance to json format.
        """
        trc_dict = copy.deepcopy(self.dict(with_signatures))
        key = trc_dict[RAINS_STRING][ONLINE_KEY_STRING]
        trc_dict[RAINS_STRING][ONLINE_KEY_STRING] = base64.b64encode(key).decode('utf-8')
        key = trc_dict[RAINS_STRING][ROOT_RAINS_KEY_STRING]
        trc_dict[RAINS_STRING][ROOT_RAINS_KEY_STRING] = base64.b64encode(key).decode('utf-8')
        core_ases = {}
        for subject in trc_dict[CORE_ASES_STRING]:
            d = trc_dict[CORE_ASES_STRING][subject]
            for key in (ONLINE_KEY_STRING, OFFLINE_KEY_STRING, ):
                key_ = trc_dict[CORE_ASES_STRING][subject][key]
                d[key] = base64.b64encode(key_).decode('utf-8')
            core_ases[subject] = d
        trc_dict[CORE_ASES_STRING] = core_ases
        root_cas = {}
        for subject in trc_dict[ROOT_CAS_STRING]:
            d = trc_dict[ROOT_CAS_STRING][subject]
            for key in (ONLINE_KEY_STRING, CERTIFICATE_STRING, ):
                key_ = trc_dict[ROOT_CAS_STRING][subject][key]
                d[key] = base64.b64encode(key_).decode('utf-8')
            root_cas[subject] = d
        trc_dict[ROOT_CAS_STRING] = root_cas
        if with_signatures:
            signatures = {}
            for subject in trc_dict[SIGNATURES_STRING]:
                signature = trc_dict[SIGNATURES_STRING][subject]
                signatures[subject] = base64.b64encode(
                    signature).decode('utf-8')
            trc_dict[SIGNATURES_STRING] = signatures
        trc_str = json.dumps(trc_dict, sort_keys=True, indent=4)
        return trc_str

    def get_ca_sigs(self):
        """
        Returns a list of tuples (isd, ca name, ca signature) for all CA
        signatures on this TRC
        """
        cas = []
        for subject, signature in self.signatures.items():
            res = self._parse_subject_str(subject)
            if not res:
                continue
            type_, isd, ca_name = res
            if type_ == "CA":
                cas.append((int(isd), ca_name, signature))
        return cas

    def get_rains_sigs(self):
        """
        Returns a list of tuples (isd, rains signature) for all RAINS signatures
        on this TRC
        """
        rains = []
        for subject, signature in self.signatures.items():
            res = self._parse_subject_str(subject)
            if not res:
                continue
            type_, isd, _ = res
            if type_ == "RAINS":
                rains.append((int(isd), signature))
        return rains

    def get_as_sigs(self):
        """
        Returns a list of tuples (isd_as, as signature) for all AS signatures
        on this TRC
        """
        ases = []
        for subject, signature in self.signatures.items():
            res = self._parse_subject_str(subject)
            if not res:
                continue
            type_, isd_as, _ = res
            if type_ == "AS":
                ases.append((isd_as, signature))
        return ases

    def get_neighbors(self):
        """
        Parses the signature subjects and returns a list of all
        ISDs which signed this TRC.
        """
        neighbors = set()
        for subject, signature in self.signatures.items():
            res = self._parse_subject_str(subject)
            if not res:
                continue
            _, isd, _ = res
            if isinstance(isd, ISD_AS):
                isd = isd[0]
            neighbors.add(isd)
        return neighbors

    def _parse_subject_str(self, subject):
        """
        Parses the subject string only for cross signatures.

        The subject strings have the different forms depending on subject.
        CA entry begins with the string "ISD x, CA:", on which the CAs name follows.
        RAINS entry begins with the string "ISD x, RAINS:"
        Core AS entry contains the SCION name of the AS.
        """
        sub = subject.split(',', 1)
        # We have a CA or rains as subject
        if sub[0].split(' ')[0] == "ISD":
            isd = sub[0].split(' ')[1]
            if not isd.isdigit() or len(sub) < 2:
                logging.error("Cannot parse subject: %s" % subject)
                return
            if sub[1].strip() == "RAINS":
                return "RAINS", isd, ""
            elif sub[1].strip().startswith('CA:'):
                ca = sub[1].split(':')[1].strip()
                return "CA", isd, ca
            else:
                logging.error("Cannot parse subject: %s" % subject)
                return
        # We have any AS
        else:
            try:
                isd_as = ISD_AS(sub[0])
                return "AS", isd_as, ""
            except:
                logging.error("Cannot parse subject: %s" % subject)
                return

    def pack(self, lz4_=False):
        ret = self.to_json().encode('utf-8')
        if lz4_:
            return lz4.dumps(ret)
        return ret

    def __str__(self):
        return self.to_json()

    def __eq__(self, other):  # pragma: no cover
        return str(self) == str(other)


def verify_new_trc(old_trc, new_trc):
    """
    Check if update from current TRC to updated TRC is valid. Checks if update
    is correct and checks if the new TRC has enough valid signatures as defined
    in the current TRC.

    :returns: True if update is valid, False otherwise
    """
    # Check if update is correct
    if old_trc.isd != new_trc.isd:
        logging.error("TRC isdid mismatch")
        return False
    if old_trc.version + 1 != new_trc.version:
        logging.error("TRC versions mismatch")
        return False
    if new_trc.time < old_trc.time:
        logging.error("New TRC timestamp is not valid")
        return False
    if old_trc.exp_time >= time.time():
        logging.error("Current TRC expired")
        return False
    if new_trc.exp_time >= time.time():
        logging.error("New TRC expired")
        return False
    if new_trc.quarantine or old_trc.quarantine:
        logging.error("Early announcement")
        return False
    # Check if there are enough valid signatures for new TRC
    if not new_trc.verify(old_trc):
        logging.error("New TRC verification failed, missing or invalid signatures")
        return False
    logging.debug("New TRC verified")
    return True


def verify_trc_chain(local_trc, verified_rem_trcs, rem_trc):
    """
    Checks if remote TRC can be verified using local TRC or already
    verified remote TRCs. i.e. checks if there is a trust chain between
    local TRC and remote TRC.

    :param TRC local_trc: The local TRC to this ISD.
    :param List(TRC) verified_rem_trcs: Already verified remote TRCs.
    :param TRC rem_trc: Remote TRC to verify.
    :returns: True if rem_trc can be verified, false otherwise.
    """
    # Get neighbors of remote TRC
    rem_nbs = rem_trc.get_neighbors()
    if local_trc.isd in rem_nbs:
        # Try to verify with local TRC
        if verify_trc_xsigs(local_trc, rem_trc) and verify_trc_xsigs(rem_trc, local_trc):
            return True
    # Only take TRCs that are neighbors of remote TRC
    ver_trcs = [trc for trc in verified_rem_trcs if trc.isd in rem_nbs]
    for trc in ver_trcs:
        if verify_trc_xsigs(trc, rem_trc) and verify_trc_xsigs(rem_trc, trc):
            return True
    return False


def verify_trc_xsigs(src_trc, dst_trc):
    """
    Check if dst_trc is signed correctly by the ISD src_trc belongs to.

    :param TRC src_trc: The signing ISD's TRC.
    :param TRC dst_trc: The TRC whose signatures need to be checked.
    :returns: True if dst_trc is signed correctly by src_trc, False otherwise.
    """
    assert isinstance(src_trc, TRC)
    assert isinstance(dst_trc, TRC)
    if src_trc.isd == dst_trc.isd:
        logging.warning("TRCs are from the same ISD.")
        return False
    return (verify_core_as_xsigs(src_trc, dst_trc) and
            verify_rains_xsigs(src_trc, dst_trc) and
            verify_ca_xsigs(src_trc, dst_trc))


def verify_core_as_xsigs(src_trc, dst_trc):
    """
    Checks if dst_trc is signed by a core AS in src_trc.

    :param TRC src_trc: The signing ISD's TRC.
    :param TRC dst_trc: The TRC whose signatures need to be checked.
    :returns: True if dst_trc has a valid signature of a core AS in src_trc.
              False otherwise.
    """
    as_sigs = dst_trc.get_as_sigs()
    for isd_as, signature in as_sigs:
        if isd_as[0] != src_trc.isd:
            continue
        pub_key = src_trc.core_ases[str(isd_as)][ONLINE_KEY_STRING]
        if dst_trc.verify_signature(signature, pub_key):
            return True
        else:
            logging.error("TRC(ISD %s) contains invalid signature from core AS (ISD %s)"
                          % (dst_trc.isd, src_trc.isd))
    return False


def verify_rains_xsigs(src_trc, dst_trc):
    """
    Checks if dst_trc is signed by RAINS in src_trc.

    :param TRC src_trc: The signing ISD's TRC.
    :param TRC dst_trc: The TRC whose signatures need to be checked.
    :returns: True if dst_trc has a valid signature of RAINS in src_trc.
              False otherwise.
    """
    rains_sigs = dst_trc.get_rains_sigs()
    for isd, signature in rains_sigs:
        if isd != src_trc.isd:
            continue
        pub_key = src_trc.rains[ONLINE_KEY_STRING]
        if dst_trc.verify_signature(signature, pub_key):
            return True
        else:
            logging.error("TRC(ISD %s) contains invalid signature from RAINS (ISD %s)"
                          % (dst_trc.isd, src_trc.isd))
    return False


def verify_ca_xsigs(src_trc, dst_trc):
    """
    Checks if dst_trc is signed by a CA in src_trc.

    :param TRC src_trc: The signing ISD's TRC.
    :param TRC dst_trc: The TRC whose signatures need to be checked.
    :returns: True if dst_trc has a valid signature of a CA in src_trc.
              False otherwise.
    """
    ca_sigs = dst_trc.get_ca_sigs()
    for isd, ca_name, signature in ca_sigs:
        if isd != src_trc.isd:
            continue
        pub_key = src_trc.root_cas[ca_name][ONLINE_KEY_STRING]
        if dst_trc.verify_signature(signature, pub_key):
            return True
        else:
            logging.error("Remote TRC(ISD %s) contains invalid signature from CA (ISD %s)"
                          % (dst_trc.isd, src_trc.isd))
    return False