Current File : //usr/lib/python3/dist-packages/dns/tsig.py
# 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.name
import dns.rcode
import dns.rdataclass
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_SHA256_128 = dns.name.from_text("hmac-sha256-128")
HMAC_SHA384 = dns.name.from_text("hmac-sha384")
HMAC_SHA384_192 = dns.name.from_text("hmac-sha384-192")
HMAC_SHA512 = dns.name.from_text("hmac-sha512")
HMAC_SHA512_256 = dns.name.from_text("hmac-sha512-256")
GSS_TSIG = dns.name.from_text("gss-tsig")
default_algorithm = HMAC_SHA256
mac_sizes = {
HMAC_SHA1: 20,
HMAC_SHA224: 28,
HMAC_SHA256: 32,
HMAC_SHA256_128: 16,
HMAC_SHA384: 48,
HMAC_SHA384_192: 24,
HMAC_SHA512: 64,
HMAC_SHA512_256: 32,
HMAC_MD5: 16,
GSS_TSIG: 128, # This is what we assume to be the worst case!
}
class GSSTSig:
"""
GSS-TSIG TSIG implementation. This uses the GSS-API context established
in the TKEY message handshake to sign messages using GSS-API message
integrity codes, per the RFC.
In order to avoid a direct GSSAPI dependency, the keyring holds a ref
to the GSSAPI object required, rather than the key itself.
"""
def __init__(self, gssapi_context):
self.gssapi_context = gssapi_context
self.data = b""
self.name = "gss-tsig"
def update(self, data):
self.data += data
def sign(self):
# defer to the GSSAPI function to sign
return self.gssapi_context.get_signature(self.data)
def verify(self, expected):
try:
# defer to the GSSAPI function to verify
return self.gssapi_context.verify_signature(self.data, expected)
except Exception:
# note the usage of a bare exception
raise BadSignature
class GSSTSigAdapter:
def __init__(self, keyring):
self.keyring = keyring
def __call__(self, message, keyname):
if keyname in self.keyring:
key = self.keyring[keyname]
if isinstance(key, Key) and key.algorithm == GSS_TSIG:
if message:
GSSTSigAdapter.parse_tkey_and_step(key, message, keyname)
return key
else:
return None
@classmethod
def parse_tkey_and_step(cls, key, message, keyname):
# if the message is a TKEY type, absorb the key material
# into the context using step(); this is used to allow the
# client to complete the GSSAPI negotiation before attempting
# to verify the signed response to a TKEY message exchange
try:
rrset = message.find_rrset(
message.answer, keyname, dns.rdataclass.ANY, dns.rdatatype.TKEY
)
if rrset:
token = rrset[0].key
gssapi_context = key.secret
return gssapi_context.step(token)
except KeyError:
pass
class HMACTSig:
"""
HMAC TSIG implementation. This uses the HMAC python module to handle the
sign/verify operations.
"""
_hashes = {
HMAC_SHA1: hashlib.sha1,
HMAC_SHA224: hashlib.sha224,
HMAC_SHA256: hashlib.sha256,
HMAC_SHA256_128: (hashlib.sha256, 128),
HMAC_SHA384: hashlib.sha384,
HMAC_SHA384_192: (hashlib.sha384, 192),
HMAC_SHA512: hashlib.sha512,
HMAC_SHA512_256: (hashlib.sha512, 256),
HMAC_MD5: hashlib.md5,
}
def __init__(self, key, algorithm):
try:
hashinfo = self._hashes[algorithm]
except KeyError:
raise NotImplementedError(f"TSIG algorithm {algorithm} is not supported")
# create the HMAC context
if isinstance(hashinfo, tuple):
self.hmac_context = hmac.new(key, digestmod=hashinfo[0])
self.size = hashinfo[1]
else:
self.hmac_context = hmac.new(key, digestmod=hashinfo)
self.size = None
self.name = self.hmac_context.name
if self.size:
self.name += f"-{self.size}"
def update(self, data):
return self.hmac_context.update(data)
def sign(self):
# defer to the HMAC digest() function for that digestmod
digest = self.hmac_context.digest()
if self.size:
digest = digest[: (self.size // 8)]
return digest
def verify(self, expected):
# re-digest and compare the results
mac = self.sign()
if not hmac.compare_digest(mac, expected):
raise BadSignature
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: dns.tsig.HMACTSig or dns.tsig.GSSTSig 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: dns.tsig.HMACTSig or dns.tsig.GSSTSig 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, dns.tsig.HMACTSig or dns.tsig.GSSTSig 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.sign()
tsig = rdata.replace(time_signed=time, mac=mac)
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: dns.tsig.HMACTSig or dns.tsig.GSSTSig 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)
ctx.verify(rdata.mac)
return _maybe_start_digest(key, rdata.mac, multi)
def get_context(key):
"""Returns an HMAC context for the specified key.
@rtype: HMAC context
@raises NotImplementedError: I{algorithm} is not supported
"""
if key.algorithm == GSS_TSIG:
return GSSTSig(key.secret)
else:
return HMACTSig(key.secret, key.algorithm)
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
)
def __repr__(self):
r = f"<DNS key name='{self.name}', " + f"algorithm='{self.algorithm}'"
if self.algorithm != GSS_TSIG:
r += f", secret='{base64.b64encode(self.secret).decode()}'"
r += ">"
return r
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