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# Copyright (C) 2001-2007, 2009, 2010 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 dns.exception
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
default_algorithm = "HMAC-MD5.SIG-ALG.REG.INT"
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)
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
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
"""
hashes = {}
try:
import hashlib
hashes[dns.name.from_text('hmac-sha224')] = hashlib.sha224
hashes[dns.name.from_text('hmac-sha256')] = hashlib.sha256
hashes[dns.name.from_text('hmac-sha384')] = hashlib.sha384
hashes[dns.name.from_text('hmac-sha512')] = hashlib.sha512
hashes[dns.name.from_text('hmac-sha1')] = hashlib.sha1
hashes[dns.name.from_text('HMAC-MD5.SIG-ALG.REG.INT')] = hashlib.md5
import sys
if sys.hexversion < 0x02050000:
# hashlib doesn't conform to PEP 247: API for
# Cryptographic Hash Functions, which hmac before python
# 2.5 requires, so add the necessary items.
class HashlibWrapper:
def __init__(self, basehash):
self.basehash = basehash
self.digest_size = self.basehash().digest_size
def new(self, *args, **kwargs):
return self.basehash(*args, **kwargs)
for name in hashes:
hashes[name] = HashlibWrapper(hashes[name])
except ImportError:
import md5, sha
hashes[dns.name.from_text('HMAC-MD5.SIG-ALG.REG.INT')] = md5.md5
hashes[dns.name.from_text('hmac-sha1')] = sha.sha
if isinstance(algorithm, (str, unicode)):
algorithm = dns.name.from_text(algorithm)
if algorithm in hashes:
return (algorithm.to_digestable(), hashes[algorithm])
raise NotImplementedError("TSIG algorithm " + str(algorithm) +
" is not supported")
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