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Filename : dnssec.py
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# Copyright (C) 2003-2007, 2009, 2011 Nominum, Inc.
#
# Permission to use, copy, modify, and distribute this software and its
# documentation for any purpose with or without fee is hereby granted,
# provided that the above copyright notice and this permission notice
# appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND NOMINUM DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NOMINUM BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
# OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

"""Common DNSSEC-related functions and constants."""

import cStringIO
import struct
import time

import dns.exception
import dns.hash
import dns.name
import dns.node
import dns.rdataset
import dns.rdata
import dns.rdatatype
import dns.rdataclass

class UnsupportedAlgorithm(dns.exception.DNSException):
    """Raised if an algorithm is not supported."""
    pass

class ValidationFailure(dns.exception.DNSException):
    """The DNSSEC signature is invalid."""
    pass

RSAMD5 = 1
DH = 2
DSA = 3
ECC = 4
RSASHA1 = 5
DSANSEC3SHA1 = 6
RSASHA1NSEC3SHA1 = 7
RSASHA256 = 8
RSASHA512 = 10
ECDSAP256SHA256 = 13
ECDSAP384SHA384 = 14
INDIRECT = 252
PRIVATEDNS = 253
PRIVATEOID = 254

_algorithm_by_text = {
    'RSAMD5' : RSAMD5,
    'DH' : DH,
    'DSA' : DSA,
    'ECC' : ECC,
    'RSASHA1' : RSASHA1,
    'DSANSEC3SHA1' : DSANSEC3SHA1,
    'RSASHA1NSEC3SHA1' : RSASHA1NSEC3SHA1,
    'RSASHA256' : RSASHA256,
    'RSASHA512' : RSASHA512,
    'INDIRECT' : INDIRECT,
    'ECDSAP256SHA256' : ECDSAP256SHA256,
    'ECDSAP384SHA384' : ECDSAP384SHA384,
    'PRIVATEDNS' : PRIVATEDNS,
    'PRIVATEOID' : PRIVATEOID,
    }

# We construct the inverse mapping programmatically to ensure that we
# cannot make any mistakes (e.g. omissions, cut-and-paste errors) that
# would cause the mapping not to be true inverse.

_algorithm_by_value = dict([(y, x) for x, y in _algorithm_by_text.iteritems()])

def algorithm_from_text(text):
    """Convert text into a DNSSEC algorithm value
    @rtype: int"""

    value = _algorithm_by_text.get(text.upper())
    if value is None:
        value = int(text)
    return value

def algorithm_to_text(value):
    """Convert a DNSSEC algorithm value to text
    @rtype: string"""

    text = _algorithm_by_value.get(value)
    if text is None:
        text = str(value)
    return text

def _to_rdata(record, origin):
    s = cStringIO.StringIO()
    record.to_wire(s, origin=origin)
    return s.getvalue()

def key_id(key, origin=None):
    rdata = _to_rdata(key, origin)
    if key.algorithm == RSAMD5:
        return (ord(rdata[-3]) << 8) + ord(rdata[-2])
    else:
        total = 0
        for i in range(len(rdata) // 2):
            total += (ord(rdata[2 * i]) << 8) + ord(rdata[2 * i + 1])
        if len(rdata) % 2 != 0:
            total += ord(rdata[len(rdata) - 1]) << 8
        total += ((total >> 16) & 0xffff);
        return total & 0xffff

def make_ds(name, key, algorithm, origin=None):
    if algorithm.upper() == 'SHA1':
        dsalg = 1
        hash = dns.hash.get('SHA1')()
    elif algorithm.upper() == 'SHA256':
        dsalg = 2
        hash = dns.hash.get('SHA256')()
    else:
        raise UnsupportedAlgorithm, 'unsupported algorithm "%s"' % algorithm

    if isinstance(name, (str, unicode)):
        name = dns.name.from_text(name, origin)
    hash.update(name.canonicalize().to_wire())
    hash.update(_to_rdata(key, origin))
    digest = hash.digest()

    dsrdata = struct.pack("!HBB", key_id(key), key.algorithm, dsalg) + digest
    return dns.rdata.from_wire(dns.rdataclass.IN, dns.rdatatype.DS, dsrdata, 0,
                               len(dsrdata))

def _find_candidate_keys(keys, rrsig):
    candidate_keys=[]
    value = keys.get(rrsig.signer)
    if value is None:
        return None
    if isinstance(value, dns.node.Node):
        try:
            rdataset = value.find_rdataset(dns.rdataclass.IN,
                                           dns.rdatatype.DNSKEY)
        except KeyError:
            return None
    else:
        rdataset = value
    for rdata in rdataset:
        if rdata.algorithm == rrsig.algorithm and \
               key_id(rdata) == rrsig.key_tag:
            candidate_keys.append(rdata)
    return candidate_keys

def _is_rsa(algorithm):
    return algorithm in (RSAMD5, RSASHA1,
                         RSASHA1NSEC3SHA1, RSASHA256,
                         RSASHA512)

def _is_dsa(algorithm):
    return algorithm in (DSA, DSANSEC3SHA1)

def _is_ecdsa(algorithm):
    return _have_ecdsa and (algorithm in (ECDSAP256SHA256, ECDSAP384SHA384))

def _is_md5(algorithm):
    return algorithm == RSAMD5

def _is_sha1(algorithm):
    return algorithm in (DSA, RSASHA1,
                         DSANSEC3SHA1, RSASHA1NSEC3SHA1)

def _is_sha256(algorithm):
    return algorithm in (RSASHA256, ECDSAP256SHA256)

def _is_sha384(algorithm):
    return algorithm == ECDSAP384SHA384

def _is_sha512(algorithm):
    return algorithm == RSASHA512

def _make_hash(algorithm):
    if _is_md5(algorithm):
        return dns.hash.get('MD5')()
    if _is_sha1(algorithm):
        return dns.hash.get('SHA1')()
    if _is_sha256(algorithm):
        return dns.hash.get('SHA256')()
    if _is_sha384(algorithm):
        return dns.hash.get('SHA384')()
    if _is_sha512(algorithm):
        return dns.hash.get('SHA512')()
    raise ValidationFailure, 'unknown hash for algorithm %u' % algorithm

def _make_algorithm_id(algorithm):
    if _is_md5(algorithm):
        oid = [0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x02, 0x05]
    elif _is_sha1(algorithm):
        oid = [0x2b, 0x0e, 0x03, 0x02, 0x1a]
    elif _is_sha256(algorithm):
        oid = [0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01]
    elif _is_sha512(algorithm):
        oid = [0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03]
    else:
        raise ValidationFailure, 'unknown algorithm %u' % algorithm
    olen = len(oid)
    dlen = _make_hash(algorithm).digest_size
    idbytes = [0x30] + [8 + olen + dlen] + \
              [0x30, olen + 4] + [0x06, olen] + oid + \
              [0x05, 0x00] + [0x04, dlen]
    return ''.join(map(chr, idbytes))

def _validate_rrsig(rrset, rrsig, keys, origin=None, now=None):
    """Validate an RRset against a single signature rdata

    The owner name of the rrsig is assumed to be the same as the owner name
    of the rrset.

    @param rrset: The RRset to validate
    @type rrset: dns.rrset.RRset or (dns.name.Name, dns.rdataset.Rdataset)
    tuple
    @param rrsig: The signature rdata
    @type rrsig: dns.rrset.Rdata
    @param keys: The key dictionary.
    @type keys: a dictionary keyed by dns.name.Name with node or rdataset values
    @param origin: The origin to use for relative names
    @type origin: dns.name.Name or None
    @param now: The time to use when validating the signatures.  The default
    is the current time.
    @type now: int
    """

    if isinstance(origin, (str, unicode)):
        origin = dns.name.from_text(origin, dns.name.root)

    for candidate_key in _find_candidate_keys(keys, rrsig):
        if not candidate_key:
            raise ValidationFailure, 'unknown key'

        # For convenience, allow the rrset to be specified as a (name, rdataset)
        # tuple as well as a proper rrset
        if isinstance(rrset, tuple):
            rrname = rrset[0]
            rdataset = rrset[1]
        else:
            rrname = rrset.name
            rdataset = rrset

        if now is None:
            now = time.time()
        if rrsig.expiration < now:
            raise ValidationFailure, 'expired'
        if rrsig.inception > now:
            raise ValidationFailure, 'not yet valid'

        hash = _make_hash(rrsig.algorithm)

        if _is_rsa(rrsig.algorithm):
            keyptr = candidate_key.key
            (bytes,) = struct.unpack('!B', keyptr[0:1])
            keyptr = keyptr[1:]
            if bytes == 0:
                (bytes,) = struct.unpack('!H', keyptr[0:2])
                keyptr = keyptr[2:]
            rsa_e = keyptr[0:bytes]
            rsa_n = keyptr[bytes:]
            keylen = len(rsa_n) * 8
            pubkey = Crypto.PublicKey.RSA.construct(
                (Crypto.Util.number.bytes_to_long(rsa_n),
                 Crypto.Util.number.bytes_to_long(rsa_e)))
            sig = (Crypto.Util.number.bytes_to_long(rrsig.signature),)
        elif _is_dsa(rrsig.algorithm):
            keyptr = candidate_key.key
            (t,) = struct.unpack('!B', keyptr[0:1])
            keyptr = keyptr[1:]
            octets = 64 + t * 8
            dsa_q = keyptr[0:20]
            keyptr = keyptr[20:]
            dsa_p = keyptr[0:octets]
            keyptr = keyptr[octets:]
            dsa_g = keyptr[0:octets]
            keyptr = keyptr[octets:]
            dsa_y = keyptr[0:octets]
            pubkey = Crypto.PublicKey.DSA.construct(
                (Crypto.Util.number.bytes_to_long(dsa_y),
                 Crypto.Util.number.bytes_to_long(dsa_g),
                 Crypto.Util.number.bytes_to_long(dsa_p),
                 Crypto.Util.number.bytes_to_long(dsa_q)))
            (dsa_r, dsa_s) = struct.unpack('!20s20s', rrsig.signature[1:])
            sig = (Crypto.Util.number.bytes_to_long(dsa_r),
                   Crypto.Util.number.bytes_to_long(dsa_s))
        elif _is_ecdsa(rrsig.algorithm):
            if rrsig.algorithm == ECDSAP256SHA256:
                curve = ecdsa.curves.NIST256p
                key_len = 32
                digest_len = 32
            elif rrsig.algorithm == ECDSAP384SHA384:
                curve = ecdsa.curves.NIST384p
                key_len = 48
                digest_len = 48
            else:
                # shouldn't happen
                raise ValidationFailure, 'unknown ECDSA curve'
            keyptr = candidate_key.key
            x = Crypto.Util.number.bytes_to_long(keyptr[0:key_len])
            y = Crypto.Util.number.bytes_to_long(keyptr[key_len:key_len * 2])
            assert ecdsa.ecdsa.point_is_valid(curve.generator, x, y)
            point = ecdsa.ellipticcurve.Point(curve.curve, x, y, curve.order)
            verifying_key = ecdsa.keys.VerifyingKey.from_public_point(point,
                                                                      curve)
            pubkey = ECKeyWrapper(verifying_key, key_len)
            r = rrsig.signature[:key_len]
            s = rrsig.signature[key_len:]
            sig = ecdsa.ecdsa.Signature(Crypto.Util.number.bytes_to_long(r),
                                        Crypto.Util.number.bytes_to_long(s))
        else:
            raise ValidationFailure, 'unknown algorithm %u' % rrsig.algorithm

        hash.update(_to_rdata(rrsig, origin)[:18])
        hash.update(rrsig.signer.to_digestable(origin))

        if rrsig.labels < len(rrname) - 1:
            suffix = rrname.split(rrsig.labels + 1)[1]
            rrname = dns.name.from_text('*', suffix)
        rrnamebuf = rrname.to_digestable(origin)
        rrfixed = struct.pack('!HHI', rdataset.rdtype, rdataset.rdclass,
                              rrsig.original_ttl)
        rrlist = sorted(rdataset);
        for rr in rrlist:
            hash.update(rrnamebuf)
            hash.update(rrfixed)
            rrdata = rr.to_digestable(origin)
            rrlen = struct.pack('!H', len(rrdata))
            hash.update(rrlen)
            hash.update(rrdata)

        digest = hash.digest()

        if _is_rsa(rrsig.algorithm):
            # PKCS1 algorithm identifier goop
            digest = _make_algorithm_id(rrsig.algorithm) + digest
            padlen = keylen // 8 - len(digest) - 3
            digest = chr(0) + chr(1) + chr(0xFF) * padlen + chr(0) + digest
        elif _is_dsa(rrsig.algorithm) or _is_ecdsa(rrsig.algorithm):
            pass
        else:
            # Raise here for code clarity; this won't actually ever happen
            # since if the algorithm is really unknown we'd already have
            # raised an exception above
            raise ValidationFailure, 'unknown algorithm %u' % rrsig.algorithm

        if pubkey.verify(digest, sig):
            return
    raise ValidationFailure, 'verify failure'

def _validate(rrset, rrsigset, keys, origin=None, now=None):
    """Validate an RRset

    @param rrset: The RRset to validate
    @type rrset: dns.rrset.RRset or (dns.name.Name, dns.rdataset.Rdataset)
    tuple
    @param rrsigset: The signature RRset
    @type rrsigset: dns.rrset.RRset or (dns.name.Name, dns.rdataset.Rdataset)
    tuple
    @param keys: The key dictionary.
    @type keys: a dictionary keyed by dns.name.Name with node or rdataset values
    @param origin: The origin to use for relative names
    @type origin: dns.name.Name or None
    @param now: The time to use when validating the signatures.  The default
    is the current time.
    @type now: int
    """

    if isinstance(origin, (str, unicode)):
        origin = dns.name.from_text(origin, dns.name.root)

    if isinstance(rrset, tuple):
        rrname = rrset[0]
    else:
        rrname = rrset.name

    if isinstance(rrsigset, tuple):
        rrsigname = rrsigset[0]
        rrsigrdataset = rrsigset[1]
    else:
        rrsigname = rrsigset.name
        rrsigrdataset = rrsigset

    rrname = rrname.choose_relativity(origin)
    rrsigname = rrname.choose_relativity(origin)
    if rrname != rrsigname:
        raise ValidationFailure, "owner names do not match"

    for rrsig in rrsigrdataset:
        try:
            _validate_rrsig(rrset, rrsig, keys, origin, now)
            return
        except ValidationFailure, e:
            pass
    raise ValidationFailure, "no RRSIGs validated"

def _need_pycrypto(*args, **kwargs):
    raise NotImplementedError, "DNSSEC validation requires pycrypto"

try:
    import Crypto.PublicKey.RSA
    import Crypto.PublicKey.DSA
    import Crypto.Util.number
    validate = _validate
    validate_rrsig = _validate_rrsig
    _have_pycrypto = True
except ImportError:
    validate = _need_pycrypto
    validate_rrsig = _need_pycrypto
    _have_pycrypto = False

try:
    import ecdsa
    import ecdsa.ecdsa
    import ecdsa.ellipticcurve
    import ecdsa.keys
    _have_ecdsa = True

    class ECKeyWrapper(object):
        def __init__(self, key, key_len):
            self.key = key
            self.key_len = key_len
        def verify(self, digest, sig):
            diglong = Crypto.Util.number.bytes_to_long(digest)
            return self.key.pubkey.verifies(diglong, sig)

except ImportError:
    _have_ecdsa = False