# 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 hmac
import struct
import sys
import dns.exception
import dns.hash
import dns.rdataclass
import dns.name
class BadTime(dns.exception.DNSException):
"""Raised if the current time is not within the TSIG's validity time."""
pass
class BadSignature(dns.exception.DNSException):
"""Raised if the TSIG signature fails to verify."""
pass
class PeerError(dns.exception.DNSException):
"""Base class for all TSIG errors generated by the remote peer"""
pass
class PeerBadKey(PeerError):
"""Raised if the peer didn't know the key we used"""
pass
class PeerBadSignature(PeerError):
"""Raised if the peer didn't like the signature we sent"""
pass
class PeerBadTime(PeerError):
"""Raised if the peer didn't like the time we sent"""
pass
class PeerBadTruncation(PeerError):
"""Raised if the peer didn't like amount of truncation in the TSIG we sent"""
pass
# 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")
default_algorithm = HMAC_MD5
BADSIG = 16
BADKEY = 17
BADTIME = 18
BADTRUNC = 22
def sign(wire, keyname, secret, time, fudge, original_id, error,
other_data, request_mac, ctx=None, multi=False, first=True,
algorithm=default_algorithm):
"""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, string, hmac.HMAC object)
@raises ValueError: I{other_data} is too long
@raises NotImplementedError: I{algorithm} is not supported
"""
(algorithm_name, digestmod) = get_algorithm(algorithm)
if first:
ctx = hmac.new(secret, digestmod=digestmod)
ml = len(request_mac)
if ml > 0:
ctx.update(struct.pack('!H', ml))
ctx.update(request_mac)
id = struct.pack('!H', original_id)
ctx.update(id)
ctx.update(wire[2:])
if first:
ctx.update(keyname.to_digestable())
ctx.update(struct.pack('!H', dns.rdataclass.ANY))
ctx.update(struct.pack('!I', 0))
long_time = time + 0L
upper_time = (long_time >> 32) & 0xffffL
lower_time = long_time & 0xffffffffL
time_mac = struct.pack('!HIH', upper_time, lower_time, fudge)
pre_mac = algorithm_name + time_mac
ol = len(other_data)
if ol > 65535:
raise ValueError('TSIG Other Data is > 65535 bytes')
post_mac = struct.pack('!HH', error, ol) + other_data
if first:
ctx.update(pre_mac)
ctx.update(post_mac)
else:
ctx.update(time_mac)
mac = ctx.digest()
mpack = struct.pack('!H', len(mac))
tsig_rdata = pre_mac + mpack + mac + id + post_mac
if multi:
ctx = hmac.new(secret, digestmod=digestmod)
ml = len(mac)
ctx.update(struct.pack('!H', ml))
ctx.update(mac)
else:
ctx = None
return (tsig_rdata, mac, ctx)
def hmac_md5(wire, keyname, secret, time, fudge, original_id, error,
other_data, request_mac, ctx=None, multi=False, first=True,
algorithm=default_algorithm):
return sign(wire, keyname, secret, time, fudge, original_id, error,
other_data, request_mac, ctx, multi, first, algorithm)
def validate(wire, keyname, secret, now, request_mac, tsig_start, tsig_rdata,
tsig_rdlen, ctx=None, multi=False, first=True):
"""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]
current = tsig_rdata
(aname, used) = dns.name.from_wire(wire, current)
current = current + used
(upper_time, lower_time, fudge, mac_size) = \
struct.unpack("!HIHH", wire[current:current + 10])
time = ((upper_time + 0L) << 32) + (lower_time + 0L)
current += 10
mac = wire[current:current + mac_size]
current += mac_size
(original_id, error, other_size) = \
struct.unpack("!HHH", wire[current:current + 6])
current += 6
other_data = wire[current:current + other_size]
current += other_size
if current != tsig_rdata + tsig_rdlen:
raise dns.exception.FormError
if error != 0:
if error == BADSIG:
raise PeerBadSignature
elif error == BADKEY:
raise PeerBadKey
elif error == BADTIME:
raise PeerBadTime
elif error == BADTRUNC:
raise PeerBadTruncation
else:
raise PeerError('unknown TSIG error code %d' % error)
time_low = time - fudge
time_high = time + fudge
if now < time_low or now > time_high:
raise BadTime
(junk, our_mac, ctx) = sign(new_wire, keyname, secret, time, fudge,
original_id, error, other_data,
request_mac, ctx, multi, first, aname)
if (our_mac != mac):
raise BadSignature
return ctx
_hashes = None
def _maybe_add_hash(tsig_alg, hash_alg):
try:
_hashes[tsig_alg] = dns.hash.get(hash_alg)
except KeyError:
pass
def _setup_hashes():
global _hashes
_hashes = {}
_maybe_add_hash(HMAC_SHA224, 'SHA224')
_maybe_add_hash(HMAC_SHA256, 'SHA256')
_maybe_add_hash(HMAC_SHA384, 'SHA384')
_maybe_add_hash(HMAC_SHA512, 'SHA512')
_maybe_add_hash(HMAC_SHA1, 'SHA1')
_maybe_add_hash(HMAC_MD5, 'MD5')
def get_algorithm(algorithm):
"""Returns the wire format string and the hash module to use for the
specified TSIG algorithm
@rtype: (string, hash constructor)
@raises NotImplementedError: I{algorithm} is not supported
"""
global _hashes
if _hashes is None:
_setup_hashes()
if isinstance(algorithm, (str, unicode)):
algorithm = dns.name.from_text(algorithm)
if sys.hexversion < 0x02050200 and \
(algorithm == HMAC_SHA384 or algorithm == HMAC_SHA512):
raise NotImplementedError("TSIG algorithm " + str(algorithm) +
" requires Python 2.5.2 or later")
try:
return (algorithm.to_digestable(), _hashes[algorithm])
except KeyError:
raise NotImplementedError("TSIG algorithm " + str(algorithm) +
" is not supported")
def get_algorithm_and_mac(wire, tsig_rdata, tsig_rdlen):
"""Return the tsig algorithm for the specified tsig_rdata
@raises FormError: The TSIG is badly formed.
"""
current = tsig_rdata
(aname, used) = dns.name.from_wire(wire, current)
current = current + used
(upper_time, lower_time, fudge, mac_size) = \
struct.unpack("!HIHH", wire[current:current + 10])
current += 10
mac = wire[current:current + mac_size]
current += mac_size
if current > tsig_rdata + tsig_rdlen:
raise dns.exception.FormError
return (aname, mac)