feat: implement policy_flags and apply these policies to submission requests

.gitlab-ci.yml

@@ -45,7 +45,6 @@ easywksserver_gpgwksclient:
     - |
       cat > /tmp/easywks.yml <<EOF
       directory: /tmp/easywks
-      permit_unsigned_response: true  # required for gpg-wks-client compat
       httpd:
         host: 127.0.0.1
         port: 8080
@@ -53,6 +52,8 @@ easywksserver_gpgwksclient:
       domains:
         example.org:
           submission_address: webkey@example.org
+          policy_flags:
+            me.s3lph.easywks_permit-unsigned-response: true  # required for gpg-wks-client compat
       EOF
     - easywks --config /tmp/easywks.yml init
     - easywks --config /tmp/easywks.yml webserver &

easywks/config.py

@@ -3,6 +3,33 @@ import string
 import yaml
 
 
+POLICY_MAILBOX_ONLY = 'mailbox-only'
+POLICY_AUTH_SUBMIT = 'auth-submit'
+POLICY_PROTOCOL_VERSION = 'protocol-version'
+STANDARD_POLICY_FLAGS = {
+    POLICY_MAILBOX_ONLY: bool,
+    # 'dane-only': bool,  # deprecated
+    POLICY_AUTH_SUBMIT: bool,
+    POLICY_PROTOCOL_VERSION: int,
+}
+
+EASYWKS_POLICY_PREFIX = 'me.s3lph.easywks_'
+EWP_PERMIT_UNSIGNED_RESPONSE = EASYWKS_POLICY_PREFIX + 'permit-unsigned-response'
+EWP_STRIP_UNVERIFIED_UIDS = EASYWKS_POLICY_PREFIX + 'strip-unverified-uids'
+EWP_STRIP_UA_UIDS = EASYWKS_POLICY_PREFIX + 'strip-ua-uids'
+EWP_STRIP_3RDPARTY_SIGNATURES = EASYWKS_POLICY_PREFIX + 'strip-3rdparty-signatures'
+EWP_MAX_REVOKED_KEYS = EASYWKS_POLICY_PREFIX + 'max-revoked-keys'
+EWP_MINIMIZE_REVOKED_KEYS = EASYWKS_POLICY_PREFIX + 'minimize-revoked-keys'
+EASYWKS_POLICY_FLAGS = {
+    EWP_PERMIT_UNSIGNED_RESPONSE: bool,
+    EWP_STRIP_UNVERIFIED_UIDS: bool,
+    EWP_STRIP_UA_UIDS: bool,
+    EWP_STRIP_3RDPARTY_SIGNATURES: bool,
+    EWP_MAX_REVOKED_KEYS: int,
+    EWP_MINIMIZE_REVOKED_KEYS: bool,
+}
+
+
 def _validate_mailing_method(value):
     methods = ['stdout', 'smtp']
     if value not in methods:
@@ -77,6 +104,19 @@ def _validate_policy_flags(value):
         for c in flag:
             if c not in alphabet:
                 return f'has invalid key {flag}'
+        if '_' in flag:
+            if flag.startswith(EASYWKS_POLICY_PREFIX):
+                cls = EASYWKS_POLICY_FLAGS.get(flag)
+                if flag not in EASYWKS_POLICY_FLAGS:
+                    return f'unknown policy flag {flag}'
+                if not isinstance(v, cls):
+                    return f'invalid type {v.__class__.__name__} for flag {flag}'
+        else:
+            cls = STANDARD_POLICY_FLAGS.get(flag)
+            if flag not in STANDARD_POLICY_FLAGS:
+                return f'unknown policy flag {flag}'
+            if not isinstance(v, cls):
+                return f'invalid type {v.__class__.__name__} for flag {flag}'
 
 
 def _validate_responses(value):
@@ -201,6 +241,7 @@ Config = _GlobalConfig(
     working_directory=_ConfigOption('directory', str, '/var/lib/easywks'),
     pending_lifetime=_ConfigOption('pending_lifetime', int, 604800),
     mailing_method=_ConfigOption('mailing_method', str, 'stdout', validator=_validate_mailing_method),
+    # TODO: permit_unsigned_response is deprecated, but for now retained for backwards compatibility
     permit_unsigned_response=_ConfigOption('permit_unsigned_response', bool, False),
     httpd=_ConfigOption('httpd', dict, {
         'host': 'localhost',

easywks/files.py

@@ -36,10 +36,15 @@ def make_submission_address_file(domain: str):
 def make_policy_file(domain: str):
     content = f'submission-address: {Config[domain].submission_address}\n'
     for flag, value in Config[domain].policy_flags.items():
-        if not value or len(value) == 0:
+        if isinstance(value, bool):
-            content += f'{flag}: {value}\n'
+            if not value:
-        else:
+                continue
+            else:
+                content += flag + '\n'
+        elif value is None:
             content += flag + '\n'
+        else:
+            content += f'{flag}: {value}\n'
     return content
 
 

easywks/process.py

@@ -1,9 +1,11 @@
 import sys
-from typing import List, Dict, Tuple
+from typing import Any, List, Dict, Tuple
 
 from .crypto import pgp_decrypt
 from .mailing import get_mailing_method
-from .config import Config
+from .config import Config, \
+    POLICY_MAILBOX_ONLY, EWP_MAX_REVOKED_KEYS, EWP_STRIP_UNVERIFIED_UIDS, EWP_STRIP_3RDPARTY_SIGNATURES, \
+    EWP_STRIP_UA_UIDS, EWP_MINIMIZE_REVOKED_KEYS, EWP_PERMIT_UNSIGNED_RESPONSE, POLICY_AUTH_SUBMIT
 from .files import read_pending_key, write_public_key, remove_pending_key, write_pending_key
 from .types import SubmissionRequest, ConfirmationResponse, PublishResponse, ConfirmationRequest, EasyWksError,\
     XLOOP_HEADER
@@ -15,7 +17,7 @@ from email.parser import BytesParser
 from email.policy import default
 from email.utils import getaddresses
 
-from pgpy import PGPMessage, PGPKey, PGPUID
+from pgpy import PGPMessage, PGPKey, PGPUID, PGPSignature
 from pgpy.errors import PGPError
 
 
@@ -134,6 +136,62 @@ def _parse_confirmation_response(pgp: PGPMessage, submission: str, sender: str):
     return ConfirmationResponse(rdict['sender'], submission, rdict['nonce'], pgp)
 
 
+# There is no API for directly removing a PGPUID or PGPSignature object
+# noinspection PyProtectedMember
+def _apply_submission_policy(request: SubmissionRequest, policy: Dict[str, Any]):
+    # Policy: Only permit a certain amount of revoked keys
+    maxrevoke = policy.get(EWP_MAX_REVOKED_KEYS, -1)
+    if maxrevoke > -1 and len(request.revoked_keys) > maxrevoke:
+        raise EasyWksError(f'Submission request contains {len(request.revoked_keys)} revoked keys.  '
+                           f'Policy permits not more than {maxrevoke}')
+    uid: PGPUID
+    revfprs = [fingerprint(request.key)] + [fingerprint(rk) for rk in request.revoked_keys]
+    for key in [request.key] + request.revoked_keys:
+        # Policy: Strip user attribute (image) UIDs
+        if policy.get(POLICY_MAILBOX_ONLY, False) or policy.get(EWP_STRIP_UA_UIDS, False):
+            for uid in list(key.userattributes):
+                uid._parent = None
+                key._uids.remove(uid)
+        # Policy: Reject keys as invalid if they contain UIDs with non-empty name or comment parts
+        if policy.get(POLICY_MAILBOX_ONLY, False):
+            for uid in list(key.userids):
+                if uid.email == '' or uid.name != '' or uid.comment != '':
+                    raise EasyWksError('This WKS server only accepts UIDs without name and comment parts')
+        # Policy: Strip all UIDs except the one being verified
+        if policy.get(EWP_STRIP_UNVERIFIED_UIDS, False):
+            for uid in list(key.userids):
+                if uid.email != request.submitter_address:
+                    uid._parent = None
+                    key._uids.remove(uid)
+        # Policy: Strip all 3rd party signatures from they key
+        if policy.get(EWP_STRIP_3RDPARTY_SIGNATURES, False):
+            for uid in list(key.userids):
+                for sig in list(uid.third_party_certifications):
+                    # Keep signatures signed by the revoked keys
+                    sig: PGPSignature
+                    if sig.signer_fingerprint not in revfprs:
+                        uid._signatures.remove(sig)
+    # Policy: Produce minimal transportable keys
+    if policy.get(EWP_MINIMIZE_REVOKED_KEYS, False):
+        for key in request.revoked_keys:
+            for uid in list(key.userids):
+                # Delete all but the submitter UIDs, and all 3rd party signatures
+                if uid.email != request.submitter_address:
+                    uid._parent = None
+                    key._uids.remove(uid)
+                else:
+                    for sig in list(uid.third_party_certifications):
+                        uid._signatures.remove(sig)
+            # Delete UAs
+            for uid in list(key.userattributes):
+                uid._parent = None
+                key._uids.remove(uid)
+            # Delete subkeys
+            for subkey in key._children.values():
+                subkey._parent = None
+            key._children.clear()
+
+
 def process_mail(mail: bytes):
     try:
         msg: Message = BytesParser(policy=default).parsebytes(mail)
@@ -170,17 +228,25 @@ def process_mail(mail: bytes):
             except FileNotFoundError:
                 raise EasyWksError('There is no submission request for this email address, or it has expired. '
                                    'Please resubmit your submission request.')
-            # this throws an error if signature verification fails
+            # TODO: Config.permit_unsigned_response is deprecated, but for now retained for backwards compatibility
-            request.verify_signature(key)
+            if not Config[sender_domain].policy_flags.get(EWP_PERMIT_UNSIGNED_RESPONSE, False) and \
+                    not Config.permit_unsigned_response:
+                # this throws an error if signature verification fails
+                request.verify_signature(key)
             response: PublishResponse = request.get_publish_response(key)
-            rmsg = response.create_signed_message()
             write_public_key(sender_domain, sender_mail, key, revoked_keys)
             remove_pending_key(sender_domain, request.nonce)
         else:
             request: SubmissionRequest = _parse_submission_request(decrypted, submission_address, sender_mail)
-            response: ConfirmationRequest = request.confirmation_request()
+            policy = Config[sender_domain].policy_flags
-            rmsg = response.create_signed_message()
+            _apply_submission_policy(request, policy)
-            write_pending_key(sender_domain, response.nonce, request.key, request.revoked_keys)
+            if policy.get(POLICY_AUTH_SUBMIT, False):
+                response = PublishResponse(request.submitter_address, request.submission_address, request.key)
+                write_public_key(sender_domain, sender_mail, request.key, request.revoked_keys)
+            else:
+                response: ConfirmationRequest = request.confirmation_request()
+                write_pending_key(sender_domain, response.nonce, request.key, request.revoked_keys)
+        rmsg = response.create_signed_message()
     except EasyWksError as e:
         rmsg = e.create_message(sender_mail, submission_address)
     method = get_mailing_method(Config.mailing_method)

easywks/types.py

@@ -13,7 +13,7 @@ from pgpy import PGPKey, PGPMessage, PGPUID
 from pgpy.errors import PGPError
 
 from .crypto import pgp_sign
-from .config import Config, render_message
+from .config import render_message
 from .util import create_nonce, fingerprint
 
 
@@ -145,13 +145,9 @@ class ConfirmationResponse:
 
     def verify_signature(self, key: PGPKey):
         if not self._msg.is_signed:
-            if not Config.permit_unsigned_response:
+            raise EasyWksError('The confirmation response is not signed. If you used an automated tool such as '
-                raise EasyWksError('The confirmation response is not signed. If you used an automated tool such as '
+                               'gpg-wks-client for submitting your response, please update said tool or try '
-                                   'gpg-wks-client for submitting your response, please update said tool or try '
+                               'responding manually.')
-                                   'responding manually.')
-            else:
-                # Unsigned, but permitted
-                return
         uid: PGPUID = key.get_uid(self._submitter_addr)
         if uid is None or uid.email != self._submitter_addr:
             raise EasyWksError(f'UID {self._submitter_addr} not found in PGP key')

package/debian/easywks/etc/easywks.yml

@@ -11,6 +11,10 @@
 # older version of the WKS standard where signing the confirmation
 # response is only recommended, but not required.  Set this option to
 # true if you want to accept such unsigned responses.
+#
+# This option is deprecated and will be removed in a future release.
+# It is replaced by the me.s3lph.easywks_permit-unsigned-response
+# per-domain policy flag.
 #permit_unsigned_response: false
 
 # Port configuration for the webserver.  Put this behind a
@@ -75,3 +79,51 @@ domains:
     # or if you're supplying your own password-protected key, set the
     # passphrase here:
     #passphrase: "Correct Horse Battery Staple"
+    # Policy flags control behavior of the submission process for this
+    # domain.  Supports most of the standard policy flags (see
+    # https://datatracker.ietf.org/doc/html/draft-koch-openpgp-webkey-service-15#section-4.5
+    # for details) as well as some EasyWKS-namespaced flags.
+    policy_flags:
+
+      # The mail server provider does only accept keys with only a
+      # mailbox in the User ID. In particular User IDs with a real name
+      # in addition to the mailbox will be rejected as invalid.
+      #mailbox-only: false
+
+      # The submission of the mail to the server is done using an
+      # authenticated connection. Thus the submitted key will be
+      # published immediately without any confirmation request.
+      #auth-submit: false
+
+      # This keyword can be used to explicitly claim the support of a
+      # specific version of the Web Key Directory update protocol. This
+      # is in general not needed but implementations may have
+      # workarounds for providers which only support an old protocol
+      # version. If these providers update to a newer version they
+      # should add this keyword so that the implementation can disable
+      # the workaround. The value is an integer corresponding to the
+      # respective draft revision number.
+      #protocol-version: null
+
+      # Some clients (including recent versions of gpg-wks-client
+      # follow an older version of the WKS standard where signing the
+      # confirmation response is only recommended, but not required.
+      # Set this option to true if you want to accept such unsigned
+      # responses.
+      #me.s3lph.easywks_permit-unsigned-response: false
+
+      # Remove all UIDs except the one being verified.
+      #me.s3lph.easywks_strip-unverified-uids: false
+
+      # Remove user attribute (i.e. photo) UIDs.
+      #me.s3lph.easywks_strip-ua-uids: false
+
+      # Remove all third party certifications fom the submitted keys.
+      # Certifications issued by revoked keys submitted in the same
+      # submission request are exempt from this policy.
+      #me.s3lph.easywks_strip-3rdparty-signatures: false
+
+      # Maximal number of revoked keys that can be submitted alongside
+      # a valid key.  If this flag is absent or has value -1, an
+      # unlimited number of revoked keys is permitted.
+      #me.s3lph.easywks_max-revoked-keys: -1