362 lines
11 KiB
Python
362 lines
11 KiB
Python
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# Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license
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# Copyright (C) 2001-2007, 2009-2011 Nominum, Inc.
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#
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# Permission to use, copy, modify, and distribute this software and its
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# documentation for any purpose with or without fee is hereby granted,
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# provided that the above copyright notice and this permission notice
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# appear in all copies.
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#
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# THE SOFTWARE IS PROVIDED "AS IS" AND NOMINUM DISCLAIMS ALL WARRANTIES
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# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NOMINUM BE LIABLE FOR
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# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
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# OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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"""DNS TSIG support."""
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import base64
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import hashlib
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import hmac
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import struct
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import dns.exception
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import dns.name
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import dns.rcode
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import dns.rdataclass
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class BadTime(dns.exception.DNSException):
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"""The current time is not within the TSIG's validity time."""
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class BadSignature(dns.exception.DNSException):
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"""The TSIG signature fails to verify."""
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class BadKey(dns.exception.DNSException):
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"""The TSIG record owner name does not match the key."""
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class BadAlgorithm(dns.exception.DNSException):
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"""The TSIG algorithm does not match the key."""
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class PeerError(dns.exception.DNSException):
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"""Base class for all TSIG errors generated by the remote peer"""
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class PeerBadKey(PeerError):
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"""The peer didn't know the key we used"""
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class PeerBadSignature(PeerError):
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"""The peer didn't like the signature we sent"""
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class PeerBadTime(PeerError):
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"""The peer didn't like the time we sent"""
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class PeerBadTruncation(PeerError):
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"""The peer didn't like amount of truncation in the TSIG we sent"""
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# TSIG Algorithms
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HMAC_MD5 = dns.name.from_text("HMAC-MD5.SIG-ALG.REG.INT")
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HMAC_SHA1 = dns.name.from_text("hmac-sha1")
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HMAC_SHA224 = dns.name.from_text("hmac-sha224")
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HMAC_SHA256 = dns.name.from_text("hmac-sha256")
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HMAC_SHA256_128 = dns.name.from_text("hmac-sha256-128")
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HMAC_SHA384 = dns.name.from_text("hmac-sha384")
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HMAC_SHA384_192 = dns.name.from_text("hmac-sha384-192")
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HMAC_SHA512 = dns.name.from_text("hmac-sha512")
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HMAC_SHA512_256 = dns.name.from_text("hmac-sha512-256")
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GSS_TSIG = dns.name.from_text("gss-tsig")
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default_algorithm = HMAC_SHA256
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mac_sizes = {
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HMAC_SHA1: 20,
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HMAC_SHA224: 28,
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HMAC_SHA256: 32,
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HMAC_SHA256_128: 16,
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HMAC_SHA384: 48,
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HMAC_SHA384_192: 24,
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HMAC_SHA512: 64,
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HMAC_SHA512_256: 32,
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HMAC_MD5: 16,
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GSS_TSIG: 128, # This is what we assume to be the worst case!
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}
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class GSSTSig:
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"""
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GSS-TSIG TSIG implementation. This uses the GSS-API context established
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in the TKEY message handshake to sign messages using GSS-API message
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integrity codes, per the RFC.
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In order to avoid a direct GSSAPI dependency, the keyring holds a ref
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to the GSSAPI object required, rather than the key itself.
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"""
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def __init__(self, gssapi_context):
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self.gssapi_context = gssapi_context
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self.data = b""
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self.name = "gss-tsig"
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def update(self, data):
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self.data += data
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def sign(self):
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# defer to the GSSAPI function to sign
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return self.gssapi_context.get_signature(self.data)
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def verify(self, expected):
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try:
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# defer to the GSSAPI function to verify
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return self.gssapi_context.verify_signature(self.data, expected)
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except Exception:
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# note the usage of a bare exception
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raise BadSignature
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class GSSTSigAdapter:
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def __init__(self, keyring):
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self.keyring = keyring
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def __call__(self, message, keyname):
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if keyname in self.keyring:
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key = self.keyring[keyname]
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if isinstance(key, Key) and key.algorithm == GSS_TSIG:
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if message:
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GSSTSigAdapter.parse_tkey_and_step(key, message, keyname)
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return key
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else:
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return None
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@classmethod
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def parse_tkey_and_step(cls, key, message, keyname):
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# if the message is a TKEY type, absorb the key material
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# into the context using step(); this is used to allow the
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# client to complete the GSSAPI negotiation before attempting
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# to verify the signed response to a TKEY message exchange
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try:
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rrset = message.find_rrset(
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message.answer, keyname, dns.rdataclass.ANY, dns.rdatatype.TKEY
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)
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if rrset:
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token = rrset[0].key
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gssapi_context = key.secret
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return gssapi_context.step(token)
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except KeyError:
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pass
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class HMACTSig:
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"""
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HMAC TSIG implementation. This uses the HMAC python module to handle the
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sign/verify operations.
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"""
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_hashes = {
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HMAC_SHA1: hashlib.sha1,
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HMAC_SHA224: hashlib.sha224,
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HMAC_SHA256: hashlib.sha256,
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HMAC_SHA256_128: (hashlib.sha256, 128),
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HMAC_SHA384: hashlib.sha384,
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HMAC_SHA384_192: (hashlib.sha384, 192),
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HMAC_SHA512: hashlib.sha512,
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HMAC_SHA512_256: (hashlib.sha512, 256),
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HMAC_MD5: hashlib.md5,
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}
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def __init__(self, key, algorithm):
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try:
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hashinfo = self._hashes[algorithm]
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except KeyError:
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raise NotImplementedError(f"TSIG algorithm {algorithm} is not supported")
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# create the HMAC context
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if isinstance(hashinfo, tuple):
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self.hmac_context = hmac.new(key, digestmod=hashinfo[0])
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self.size = hashinfo[1]
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else:
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self.hmac_context = hmac.new(key, digestmod=hashinfo)
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self.size = None
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self.name = self.hmac_context.name
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if self.size:
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self.name += f"-{self.size}"
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def update(self, data):
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return self.hmac_context.update(data)
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def sign(self):
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# defer to the HMAC digest() function for that digestmod
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digest = self.hmac_context.digest()
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if self.size:
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digest = digest[: (self.size // 8)]
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return digest
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def verify(self, expected):
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# re-digest and compare the results
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mac = self.sign()
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if not hmac.compare_digest(mac, expected):
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raise BadSignature
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def _digest(wire, key, rdata, time=None, request_mac=None, ctx=None, multi=None):
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"""Return a context containing the TSIG rdata for the input parameters
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@rtype: dns.tsig.HMACTSig or dns.tsig.GSSTSig object
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@raises ValueError: I{other_data} is too long
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@raises NotImplementedError: I{algorithm} is not supported
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"""
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first = not (ctx and multi)
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if first:
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ctx = get_context(key)
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if request_mac:
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ctx.update(struct.pack("!H", len(request_mac)))
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ctx.update(request_mac)
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ctx.update(struct.pack("!H", rdata.original_id))
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ctx.update(wire[2:])
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if first:
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ctx.update(key.name.to_digestable())
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ctx.update(struct.pack("!H", dns.rdataclass.ANY))
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ctx.update(struct.pack("!I", 0))
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if time is None:
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time = rdata.time_signed
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upper_time = (time >> 32) & 0xFFFF
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lower_time = time & 0xFFFFFFFF
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time_encoded = struct.pack("!HIH", upper_time, lower_time, rdata.fudge)
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other_len = len(rdata.other)
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if other_len > 65535:
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raise ValueError("TSIG Other Data is > 65535 bytes")
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if first:
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ctx.update(key.algorithm.to_digestable() + time_encoded)
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ctx.update(struct.pack("!HH", rdata.error, other_len) + rdata.other)
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else:
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ctx.update(time_encoded)
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return ctx
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def _maybe_start_digest(key, mac, multi):
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"""If this is the first message in a multi-message sequence,
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start a new context.
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@rtype: dns.tsig.HMACTSig or dns.tsig.GSSTSig object
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"""
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if multi:
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ctx = get_context(key)
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ctx.update(struct.pack("!H", len(mac)))
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ctx.update(mac)
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return ctx
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else:
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return None
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def sign(wire, key, rdata, time=None, request_mac=None, ctx=None, multi=False):
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"""Return a (tsig_rdata, mac, ctx) tuple containing the HMAC TSIG rdata
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for the input parameters, the HMAC MAC calculated by applying the
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TSIG signature algorithm, and the TSIG digest context.
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@rtype: (string, dns.tsig.HMACTSig or dns.tsig.GSSTSig object)
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@raises ValueError: I{other_data} is too long
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@raises NotImplementedError: I{algorithm} is not supported
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"""
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ctx = _digest(wire, key, rdata, time, request_mac, ctx, multi)
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mac = ctx.sign()
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tsig = rdata.replace(time_signed=time, mac=mac)
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return (tsig, _maybe_start_digest(key, mac, multi))
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def validate(
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wire, key, owner, rdata, now, request_mac, tsig_start, ctx=None, multi=False
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):
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"""Validate the specified TSIG rdata against the other input parameters.
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@raises FormError: The TSIG is badly formed.
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@raises BadTime: There is too much time skew between the client and the
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server.
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@raises BadSignature: The TSIG signature did not validate
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@rtype: dns.tsig.HMACTSig or dns.tsig.GSSTSig object"""
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(adcount,) = struct.unpack("!H", wire[10:12])
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if adcount == 0:
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raise dns.exception.FormError
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adcount -= 1
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new_wire = wire[0:10] + struct.pack("!H", adcount) + wire[12:tsig_start]
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if rdata.error != 0:
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if rdata.error == dns.rcode.BADSIG:
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raise PeerBadSignature
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elif rdata.error == dns.rcode.BADKEY:
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raise PeerBadKey
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elif rdata.error == dns.rcode.BADTIME:
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raise PeerBadTime
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elif rdata.error == dns.rcode.BADTRUNC:
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raise PeerBadTruncation
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else:
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raise PeerError("unknown TSIG error code %d" % rdata.error)
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if abs(rdata.time_signed - now) > rdata.fudge:
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raise BadTime
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if key.name != owner:
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raise BadKey
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if key.algorithm != rdata.algorithm:
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raise BadAlgorithm
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ctx = _digest(new_wire, key, rdata, None, request_mac, ctx, multi)
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ctx.verify(rdata.mac)
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return _maybe_start_digest(key, rdata.mac, multi)
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def get_context(key):
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"""Returns an HMAC context for the specified key.
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@rtype: HMAC context
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@raises NotImplementedError: I{algorithm} is not supported
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"""
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if key.algorithm == GSS_TSIG:
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return GSSTSig(key.secret)
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else:
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return HMACTSig(key.secret, key.algorithm)
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class Key:
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def __init__(self, name, secret, algorithm=default_algorithm):
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if isinstance(name, str):
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name = dns.name.from_text(name)
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self.name = name
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if isinstance(secret, str):
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secret = base64.decodebytes(secret.encode())
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self.secret = secret
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if isinstance(algorithm, str):
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algorithm = dns.name.from_text(algorithm)
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self.algorithm = algorithm
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def __eq__(self, other):
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return (
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isinstance(other, Key)
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and self.name == other.name
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and self.secret == other.secret
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and self.algorithm == other.algorithm
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)
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def __repr__(self):
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r = f"<DNS key name='{self.name}', " + f"algorithm='{self.algorithm}'"
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if self.algorithm != GSS_TSIG:
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r += f", secret='{base64.b64encode(self.secret).decode()}'"
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r += ">"
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return r
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