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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.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