From 3dda94ca2d4bc9759521528b57115d4d1bbaff14 Mon Sep 17 00:00:00 2001 From: Scott Kitterman Date: Sat, 2 Nov 2019 11:15:36 -0400 Subject: [PATCH] Initial async support - works but so much overriding ... --- ChangeLog | 2 + README | 3 + dkim/__init__.py | 27 +++- dkim/asyncsupport.py | 286 +++++++++++++++++++++++++++++++++++++++++++ setup.py | 3 +- 5 files changed, 316 insertions(+), 5 deletions(-) create mode 100644 dkim/asyncsupport.py diff --git a/ChangeLog b/ChangeLog index 5774634..416048e 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,6 +1,8 @@ Version 1.0.0 - Add support for RFC 8460 tlsrpt DKIM signature processing (LP: #1847020) - Add new timeout parameter to enable DNS lookup timeouts to be adjusted + - Add async support with aiodns for DKIM verification (ARC not supported) + (LP: #1847002) - Drop usage of pymilter Milter.dns in dnsplug since it doesn't support havine a timeout passed to it diff --git a/README b/README index 0d3a0bd..f472afb 100644 --- a/README +++ b/README @@ -19,6 +19,8 @@ Dependencies will be automatically included for normal DKIM usage. The extras_requires feature 'ed25519' will add the dependencies needed for signing and verifying using the new DCRUP ed25519-sha256 algorithm. The extras_requires feature 'ARC' will add the extra dependencies needed for ARC. +Similarly, extras_requires feature 'asyncio' will add the extra dependencies +needed for asyncio. - Python 2.x >= 2.7, or Python 3.x >= 3.5. Recent versions have not been tested on python < 2.7 or python3 < 3.5, but may still work on python2.6 @@ -28,6 +30,7 @@ extras_requires feature 'ARC' will add the extra dependencies needed for ARC. - argparse. Standard library in python2.7 and later. - authres. Needed for ARC. - PyNaCl. Needed for use of ed25519 capability. + - aiodns. Needed for asycnio (Required python3.5 or later) INSTALLATION diff --git a/dkim/__init__.py b/dkim/__init__.py index e00908c..fd0c49f 100644 --- a/dkim/__init__.py +++ b/dkim/__init__.py @@ -36,6 +36,7 @@ import base64 import hashlib import logging import re +import sys import time # only needed for arc @@ -70,8 +71,13 @@ from dkim.crypto import ( try: from dkim.dnsplug import get_txt except ImportError: - def get_txt(s,timeout=5): - raise RuntimeError("DKIM.verify requires DNS or dnspython module") + try: + import aiodns + from dkim.asyncsupport import get_txt_async as get_txt + except: + # Only true if not using async + def get_txt(s,timeout=5): + raise RuntimeError("DKIM.verify requires DNS or dnspython module") from dkim.util import ( get_default_logger, InvalidTagValueList, @@ -419,7 +425,7 @@ def fold(header, namelen=0, linesep=b'\r\n'): return pre + header -def load_pk_from_dns(name, dnsfunc=get_txt, timeout=5): +def load_pk_from_dns(name, dnsfunc, timeout=5): s = dnsfunc(name, timeout=timeout) if not s: raise KeyFormatError("missing public key: %s"%name) @@ -1298,7 +1304,8 @@ def sign(message, selector, domain, privkey, identity=None, return d.sign(selector, domain, privkey, identity=identity, canonicalize=canonicalize, include_headers=include_headers, length=length) -def verify(message, logger=None, dnsfunc=get_txt, minkey=1024, timeout=5, tlsrpt=False): +def verify(message, logger=None, dnsfunc=get_txt, minkey=1024, + timeout=5, tlsrpt=False): """Verify the first (topmost) DKIM signature on an RFC822 formatted message. @param message: an RFC822 formatted message (with either \\n or \\r\\n line endings) @param logger: a logger to which debug info will be written (default None) @@ -1317,6 +1324,18 @@ def verify(message, logger=None, dnsfunc=get_txt, minkey=1024, timeout=5, tlsrpt logger.error("%s" % x) return False + +# aiodns requires Python 3.5+, so no async before that +if sys.version_info >= (3, 5): + try: + import aiodns + from dkim.asyncsupport import verify_async + dkim_verify_async = verify_async + except ImportError: + # If aiodns is not installed, then async verification is not available + pass + + # For consistency with ARC dkim_sign = sign dkim_verify = verify diff --git a/dkim/asyncsupport.py b/dkim/asyncsupport.py new file mode 100644 index 0000000..b9fa193 --- /dev/null +++ b/dkim/asyncsupport.py @@ -0,0 +1,286 @@ +# This software is provided 'as-is', without any express or implied +# warranty. In no event will the author be held liable for any damages +# arising from the use of this software. +# +# Permission is granted to anyone to use this software for any purpose, +# including commercial applications, and to alter it and redistribute it +# freely, subject to the following restrictions: +# +# 1. The origin of this software must not be misrepresented; you must not +# claim that you wrote the original software. If you use this software +# in a product, an acknowledgment in the product documentation would be +# appreciated but is not required. +# 2. Altered source versions must be plainly marked as such, and must not be +# misrepresented as being the original software. +# 3. This notice may not be removed or altered from any source distribution. +# +# Copyright (c) 2008 Greg Hewgill http://hewgill.com +# +# This has been modified from the original software. +# Copyright (c) 2011 William Grant +# +# This has been modified from the original software. +# Copyright (c) 2016 Google, Inc. +# Contact: Brandon Long +# +# This has been modified from the original software. +# Copyright (c) 2016, 2017, 2018, 2019 Scott Kitterman +# +# This has been modified from the original software. +# Copyright (c) 2017 Valimail Inc +# Contact: Gene Shuman + +import asyncio +import aiodns +import base64 +import dkim +import re + +__all__ = [ + 'get_txt_async', + 'load_pk_from_dns_async', + 'verify_async' + ] + + +async def get_txt_async(name, timeout=5): + """Return a TXT record associated with a DNS name in an asnyc loop. For + DKIM we can assume there is only one.""" + + # Note: This will use the existing loop or create one if needed + loop = asyncio.get_event_loop() + resolver = aiodns.DNSResolver(loop=loop, timeout=timeout) + + async def query(name, qtype): + return await resolver.query(name, qtype) + + #q = query(name, 'TXT') + try: + result = await query(name, 'TXT') + except aiodns.error.DNSError: + result = None + print('result', result) + + if result: + return result[0].text + else: + return None + + +async def load_pk_from_dns_async(name, dnsfunc, timeout=5): + s = await dnsfunc(name, timeout=timeout) + if not s: + raise dkim.KeyFormatError("missing public key: %s"%name) + try: + if type(s) is str: + s = s.encode('ascii') + pub = dkim.parse_tag_value(s) + except dkim.InvalidTagValueList as e: + raise dkim.KeyFormatError(e) + try: + if pub[b'v'] != b'DKIM1': + raise dkim.KeyFormatError("bad version") + except KeyError as e: + # Version not required in key record: RFC 6376 3.6.1 + pass + try: + if pub[b'k'] == b'ed25519': + pk = nacl.signing.VerifyKey(pub[b'p'], encoder=nacl.encoding.Base64Encoder) + keysize = 256 + ktag = b'ed25519' + except KeyError: + pub[b'k'] = b'rsa' + if pub[b'k'] == b'rsa': + try: + pk = dkim.parse_public_key(base64.b64decode(pub[b'p'])) + keysize = dkim.bitsize(pk['modulus']) + except KeyError: + raise dkim.KeyFormatError("incomplete public key: %s" % s) + except (TypeError,dkim.UnparsableKeyError) as e: + raise dkim.KeyFormatError("could not parse public key (%s): %s" % (pub[b'p'],e)) + ktag = b'rsa' + if pub[b'k'] != b'rsa' and pub[b'k'] != b'ed25519': + raise dkim.KeyFormatError('unknown algorithm in k= tag: {0}'.format(pub[b'k'])) + seqtlsrpt = False + try: + # Ignore unknown service types, RFC 6376 3.6.1 + if pub[b's'] != b'*' and pub[b's'] != b'email' and pub[b's'] != b'tlsrpt': + pk = None + keysize = None + ktag = None + raise dkim.KeyFormatError('unknown service type in s= tag: {0}'.format(pub[b's'])) + elif pub[b's'] == b'tlsrpt': + seqtlsrpt = True + except: + # Default is '*' - all service types, so no error if missing from key record + pass + return pk, keysize, ktag, seqtlsrpt + +class DKIM(dkim.DKIM): + #: Sign an RFC822 message and return the DKIM-Signature header line. + #: + #: The include_headers option gives full control over which header fields + #: are signed. Note that signing a header field that doesn't exist prevents + #: that field from being added without breaking the signature. Repeated + #: fields (such as Received) can be signed multiple times. Instances + #: of the field are signed from bottom to top. Signing a header field more + #: times than are currently present prevents additional instances + #: from being added without breaking the signature. + #: + #: The length option allows the message body to be appended to by MTAs + #: enroute (e.g. mailing lists that append unsubscribe information) + #: without breaking the signature. + #: + #: The default include_headers for this method differs from the backward + #: compatible sign function, which signs all headers not + #: in should_not_sign. The default list for this method can be modified + #: by tweaking should_sign and frozen_sign (or even should_not_sign). + #: It is only necessary to pass an include_headers list when precise control + #: is needed. + #: + #: @param selector: the DKIM selector value for the signature + #: @param domain: the DKIM domain value for the signature + #: @param privkey: a PKCS#1 private key in base64-encoded text form + #: @param identity: the DKIM identity value for the signature + #: (default "@"+domain) + #: @param canonicalize: the canonicalization algorithms to use + #: (default (Simple, Simple)) + #: @param include_headers: a list of strings indicating which headers + #: are to be signed (default rfc4871 recommended headers) + #: @param length: true if the l= tag should be included to indicate + #: body length signed (default False). + #: @return: DKIM-Signature header field terminated by '\r\n' + #: @raise DKIMException: when the message, include_headers, or key are badly + #: formed. + + # Abstract helper method to verify a signed header + #: @param sig: List of (key, value) tuples containing tag=values of the header + #: @param include_headers: headers to validate b= signature against + #: @param sig_header: (header_name, header_value) + #: @param dnsfunc: interface to dns + async def verify_sig(self, sig, include_headers, sig_header, dnsfunc): + name = sig[b's'] + b"._domainkey." + sig[b'd'] + b"." + try: + pk, self.keysize, ktag, self.seqtlsrpt = await load_pk_from_dns_async(name, dnsfunc, + timeout=self.timeout) + except dkim.KeyFormatError as e: + self.logger.error("%s" % e) + return False + + # RFC 8460 MAY ignore signatures without tlsrpt Service Type + if self.tlsrpt == 'strict' and not self.seqtlsrpt: + raise ValidationError("Message is tlsrpt and Service Type is not tlsrpt") + + # Inferred requirement from both RFC 8460 and RFC 6376 + if not self.tlsrpt and self.seqtlsrpt: + raise ValidationError("Message is not tlsrpt and Service Type is tlsrpt") + + try: + canon_policy = dkim.CanonicalizationPolicy.from_c_value(sig.get(b'c', b'simple/simple')) + except dkim.InvalidCanonicalizationPolicyError as e: + raise dkim.MessageFormatError("invalid c= value: %s" % e.args[0]) + + hasher = dkim.HASH_ALGORITHMS[sig[b'a']] + + # validate body if present + if b'bh' in sig: + h = dkim.HashThrough(hasher(), self.debug_content) + + body = canon_policy.canonicalize_body(self.body) + if b'l' in sig and not self.tlsrpt: + body = body[:int(sig[b'l'])] + h.update(body) + if self.debug_content: + self.logger.debug("body hashed: %r" % h.hashed()) + bodyhash = h.digest() + + self.logger.debug("bh: %s" % base64.b64encode(bodyhash)) + try: + bh = base64.b64decode(re.sub(br"\s+", b"", sig[b'bh'])) + except TypeError as e: + raise dkim.MessageFormatError(str(e)) + if bodyhash != bh: + raise dkim.ValidationError( + "body hash mismatch (got %s, expected %s)" % + (base64.b64encode(bodyhash), sig[b'bh'])) + + # address bug#644046 by including any additional From header + # fields when verifying. Since there should be only one From header, + # this shouldn't break any legitimate messages. This could be + # generalized to check for extras of other singleton headers. + if b'from' in include_headers: + include_headers.append(b'from') + h = dkim.HashThrough(hasher(), self.debug_content) + + headers = canon_policy.canonicalize_headers(self.headers) + self.signed_headers = dkim.hash_headers( + h, canon_policy, headers, include_headers, sig_header, sig) + if self.debug_content: + self.logger.debug("signed for %s: %r" % (sig_header[0], h.hashed())) + signature = base64.b64decode(re.sub(br"\s+", b"", sig[b'b'])) + if ktag == b'rsa': + try: + res = dkim.RSASSA_PKCS1_v1_5_verify(h, signature, pk) + self.logger.debug("%s valid: %s" % (sig_header[0], res)) + if res and self.keysize < self.minkey: + raise dkim.KeyFormatError("public key too small: %d" % self.keysize) + return res + except (TypeError,dkim.DigestTooLargeError) as e: + raise dkim.KeyFormatError("digest too large for modulus: %s"%e) + elif ktag == b'ed25519': + try: + pk.verify(h.digest(), signature) + self.logger.debug("%s valid" % (sig_header[0])) + return True + except (nacl.exceptions.BadSignatureError) as e: + return False + else: + raise dkim.UnknownKeyTypeError(ktag) + + async def verify(self,idx=0,dnsfunc=get_txt_async): + sigheaders = [(x,y) for x,y in self.headers if x.lower() == b"dkim-signature"] + if len(sigheaders) <= idx: + return False + + # By default, we validate the first DKIM-Signature line found. + try: + sig = dkim.parse_tag_value(sigheaders[idx][1]) + self.signature_fields = sig + except dkim.InvalidTagValueList as e: + raise dkim.MessageFormatError(e) + + self.logger.debug("sig: %r" % sig) + + dkim.validate_signature_fields(sig) + self.domain = sig[b'd'] + self.selector = sig[b's'] + + include_headers = [x.lower() for x in re.split(br"\s*:\s*", sig[b'h'])] + self.include_headers = tuple(include_headers) + + return await self.verify_sig(sig, include_headers, sigheaders[idx], dnsfunc) + + +async def verify_async(message, logger=None, dnsfunc=None, minkey=1024, + timeout=5, tlsrpt=False): + """Verify the first (topmost) DKIM signature on an RFC822 formatted message in an asyncio contxt. + @param message: an RFC822 formatted message (with either \\n or \\r\\n line endings) + @param logger: a logger to which debug info will be written (default None) + @param timeout: number of seconds for DNS lookup timeout (default = 5) + @param tlsrpt: message is an RFC 8460 TLS report (default False) + False: Not a tlsrpt, True: Is a tlsrpt, 'strict': tlsrpt, invalid if + service type is missing. For signing, if True, length is never used. + @return: True if signature verifies or False otherwise + """ + # type: (bytes, any, function, int) -> bool + # Note: This will use the existing loop or create one if needed + loop = asyncio.get_event_loop() + if not dnsfunc: + dnsfunc=get_txt_async + d = DKIM(message,logger=logger,minkey=minkey,timeout=timeout,tlsrpt=tlsrpt) + try: + return await d.verify(dnsfunc=dnsfunc) + except dkim.DKIMException as x: + if logger is not None: + logger.error("%s" % x) + return False diff --git a/setup.py b/setup.py index 752e168..29595f2 100644 --- a/setup.py +++ b/setup.py @@ -86,7 +86,8 @@ verification.""", 'pynacl', ], 'ed25519': ['pynacl'], - 'ARC': ['authres'] + 'ARC': ['authres'], + 'asyncio': ['aiodns'] }, **kw )