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# Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license
# Copyright (C) 2001-2007, 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.
"""DNS TSIG support."""
import base64
import hashlib
import hmac
import struct
import dns.exception
import dns.rdataclass
import dns.name
import dns.rcode
class BadTime(dns.exception.DNSException):
"""The current time is not within the TSIG's validity time."""
class BadSignature(dns.exception.DNSException):
"""The TSIG signature fails to verify."""
class BadKey(dns.exception.DNSException):
"""The TSIG record owner name does not match the key."""
class BadAlgorithm(dns.exception.DNSException):
"""The TSIG algorithm does not match the key."""
class PeerError(dns.exception.DNSException):
"""Base class for all TSIG errors generated by the remote peer"""
class PeerBadKey(PeerError):
"""The peer didn't know the key we used"""
class PeerBadSignature(PeerError):
"""The peer didn't like the signature we sent"""
class PeerBadTime(PeerError):
"""The peer didn't like the time we sent"""
class PeerBadTruncation(PeerError):
"""The peer didn't like amount of truncation in the TSIG we sent"""
# TSIG Algorithms
HMAC_MD5 = dns.name.from_text("HMAC-MD5.SIG-ALG.REG.INT")
HMAC_SHA1 = dns.name.from_text("hmac-sha1")
HMAC_SHA224 = dns.name.from_text("hmac-sha224")
HMAC_SHA256 = dns.name.from_text("hmac-sha256")
HMAC_SHA384 = dns.name.from_text("hmac-sha384")
HMAC_SHA512 = dns.name.from_text("hmac-sha512")
_hashes = {
HMAC_SHA224: hashlib.sha224,
HMAC_SHA256: hashlib.sha256,
HMAC_SHA384: hashlib.sha384,
HMAC_SHA512: hashlib.sha512,
HMAC_SHA1: hashlib.sha1,
HMAC_MD5: hashlib.md5,
}
default_algorithm = HMAC_SHA256
def _digest(wire, key, rdata, time=None, request_mac=None, ctx=None,
multi=None):
"""Return a context containing the TSIG rdata for the input parameters
@rtype: hmac.HMAC object
@raises ValueError: I{other_data} is too long
@raises NotImplementedError: I{algorithm} is not supported
"""
first = not (ctx and multi)
if first:
ctx = get_context(key)
if request_mac:
ctx.update(struct.pack('!H', len(request_mac)))
ctx.update(request_mac)
ctx.update(struct.pack('!H', rdata.original_id))
ctx.update(wire[2:])
if first:
ctx.update(key.name.to_digestable())
ctx.update(struct.pack('!H', dns.rdataclass.ANY))
ctx.update(struct.pack('!I', 0))
if time is None:
time = rdata.time_signed
upper_time = (time >> 32) & 0xffff
lower_time = time & 0xffffffff
time_encoded = struct.pack('!HIH', upper_time, lower_time, rdata.fudge)
other_len = len(rdata.other)
if other_len > 65535:
raise ValueError('TSIG Other Data is > 65535 bytes')
if first:
ctx.update(key.algorithm.to_digestable() + time_encoded)
ctx.update(struct.pack('!HH', rdata.error, other_len) + rdata.other)
else:
ctx.update(time_encoded)
return ctx
def _maybe_start_digest(key, mac, multi):
"""If this is the first message in a multi-message sequence,
start a new context.
@rtype: hmac.HMAC object
"""
if multi:
ctx = get_context(key)
ctx.update(struct.pack('!H', len(mac)))
ctx.update(mac)
return ctx
else:
return None
def sign(wire, key, rdata, time=None, request_mac=None, ctx=None, multi=False):
"""Return a (tsig_rdata, mac, ctx) tuple containing the HMAC TSIG rdata
for the input parameters, the HMAC MAC calculated by applying the
TSIG signature algorithm, and the TSIG digest context.
@rtype: (string, hmac.HMAC object)
@raises ValueError: I{other_data} is too long
@raises NotImplementedError: I{algorithm} is not supported
"""
ctx = _digest(wire, key, rdata, time, request_mac, ctx, multi)
mac = ctx.digest()
tsig = dns.rdtypes.ANY.TSIG.TSIG(dns.rdataclass.ANY, dns.rdatatype.TSIG,
key.algorithm, time, rdata.fudge, mac,
rdata.original_id, rdata.error,
rdata.other)
return (tsig, _maybe_start_digest(key, mac, multi))
def validate(wire, key, owner, rdata, now, request_mac, tsig_start, ctx=None,
multi=False):
"""Validate the specified TSIG rdata against the other input parameters.
@raises FormError: The TSIG is badly formed.
@raises BadTime: There is too much time skew between the client and the
server.
@raises BadSignature: The TSIG signature did not validate
@rtype: hmac.HMAC object"""
(adcount,) = struct.unpack("!H", wire[10:12])
if adcount == 0:
raise dns.exception.FormError
adcount -= 1
new_wire = wire[0:10] + struct.pack("!H", adcount) + wire[12:tsig_start]
if rdata.error != 0:
if rdata.error == dns.rcode.BADSIG:
raise PeerBadSignature
elif rdata.error == dns.rcode.BADKEY:
raise PeerBadKey
elif rdata.error == dns.rcode.BADTIME:
raise PeerBadTime
elif rdata.error == dns.rcode.BADTRUNC:
raise PeerBadTruncation
else:
raise PeerError('unknown TSIG error code %d' % rdata.error)
if abs(rdata.time_signed - now) > rdata.fudge:
raise BadTime
if key.name != owner:
raise BadKey
if key.algorithm != rdata.algorithm:
raise BadAlgorithm
ctx = _digest(new_wire, key, rdata, None, request_mac, ctx, multi)
mac = ctx.digest()
if not hmac.compare_digest(mac, rdata.mac):
raise BadSignature
return _maybe_start_digest(key, mac, multi)
def get_context(key):
"""Returns an HMAC context foe the specified key.
@rtype: HMAC context
@raises NotImplementedError: I{algorithm} is not supported
"""
try:
digestmod = _hashes[key.algorithm]
except KeyError:
raise NotImplementedError(f"TSIG algorithm {key.algorithm} " +
"is not supported")
return hmac.new(key.secret, digestmod=digestmod)
class Key:
def __init__(self, name, secret, algorithm=default_algorithm):
if isinstance(name, str):
name = dns.name.from_text(name)
self.name = name
if isinstance(secret, str):
secret = base64.decodebytes(secret.encode())
self.secret = secret
if isinstance(algorithm, str):
algorithm = dns.name.from_text(algorithm)
self.algorithm = algorithm
def __eq__(self, other):
return (isinstance(other, Key) and
self.name == other.name and
self.secret == other.secret and
self.algorithm == other.algorithm)